Symmetry, Integrability and Geometry: Methods and Applications SIGMA 8 (2012), 074, 16 pages
Ladder Operators for Lame´ Spheroconal
Harmonic Polynomials?
Ricardo ME´NDEZ-FRAGOSO †‡ and Eugenio LEY-KOO ‡
† Facultad de Ciencias, Universidad Nacional Auto´noma de Me´xico, Me´xico
E-mail: rich@ciencias.unam.mx
URL: http://sistemas.fciencias.unam.mx/rich/
‡ Instituto de F´ısica, Universidad Nacional Auto´noma de Me´xico, Me´xico
E-mail: eleykoo@fisica.unam.mx
Received July 31, 2012, in final form October 09, 2012; Published online October 17, 2012
http://dx.doi.org/10.3842/SIGMA.2012.074
Abstract. Three sets of ladder operators in spheroconal coordinates and their respective
actions on Lame´ spheroconal harmonic polynomials are presented in this article. The poly-
nomials are common eigenfunctions of the square of the angular momentum operator and of
the asymmetry distribution Hamiltonian for the rotations of asymmetric molecules, in the
body-fixed frame with principal axes. The first set of operators for Lame´ polynomials of
a given species and a fixed value of the square of the angular momentum raise and lower
and lower and raise in complementary ways the quantum numbers n1 and n2 counting the
respective nodal elliptical cones. The second set of operators consisting of the cartesian
components Lˆx, Lˆy, Lˆz of the angular momentum connect pairs of the four species of poly-
nomials of a chosen kind and angular momentum. The third set of operators, the cartesian
components pˆx, pˆy, pˆz of the linear momentum, connect pairs of the polynomials differing in
one unit in their angular momentum and in their parities. Relationships among spheroconal
harmonics at the levels of the three sets of operators are illustrated.
Key words: Lame´ polynomials; spheroconal harmonics; ladder operators
2010 Mathematics Subject Classification: 20C35; 22E70; 33C47; 33C80; 81R05
1 Introduction
One of our contributions to the Symposium on Superintegrability, Exact Solvability and Special
Functions dealt with the topic of “Symmetries and asymmetries in quantum systems confined
by elliptical cones”, reviewing some of our results on the rotations of free asymmetric molecules
[9, 10] and their extensions for other systems under confinement [17, 18, 19]. While the free
systems involve Lame´ spheroconal harmonic polynomial eigenfunctions, the systems confined by
elliptical cones involve quasi-periodic Lame´ eigenfunctions represented as infinite series, due to
the breaking of the parity symmetry with respect the axis of the confining cone. Nevertheless,
the methodology for the accurate and convergent evaluation of eigenvalues and eigenfunctions is
the same. The differences reside in the boundary conditions, translating into recurrence relations
of three terms and four terms for the expansion coefficients, respectively; such relations can be
cast into matrix forms which are of finite size for the free systems [10] and of infinite size for
the confined systems [17, 18, 19] leading to the corresponding polynomial and infinite series
representations. The latter can be evaluated with sufficient accuracy using finite and large
enough size matrices, testing for convergence along the way.
Concerning the conditions of exact solvability requiring polynomial solutions and ladder ope-
rators connecting them, the Lame´ spheroconal harmonics for the free systems satisfy the first
?This paper is a contribution to the Special Issue “Superintegrability, Exact Solvability, and Special Functions”.
The full collection is available at http://www.emis.de/journals/SIGMA/SESSF2012.html
2 R. Me´ndez-Fragoso and E. Ley-Koo
one and in this contribution three sets of ladder operators in the purely spheroconal formulation
are reported. It must be pointed out that one of these sets had been identified sometime ago
[13, 14, 15, 24, 25] and our recent work [18] in its section “On Developing the Theory of Angular
Momentum in Bases of Lame´ Spheroconal Harmonics” identified a second set. However, it
must also be admitted that in these treatments the connections with the spherical and cartesian
harmonic bases were used.
The material in the manuscript is distributed in the following way: Section 2 reviews briefly
the simultaneous separability of the square of the angular momentum operator and the asym-
metry distribution Hamiltonian eigenvalue equations, the integration of the Lame´ differential
equation in the respective elliptical cone coordinates, illustrating the lower eigenvalues and eigen-
functions for their matched products making up the Lame´ spheroconal harmonic polynomials.
Section 3 identifies the raising and lowering actions on the numbers n1 and n2 counting the
nodal elliptical cones in the neighboring spheroconal harmonic polynomials as their respective
eigenvalues hAn1(k
2
1) and h
B
n2(k
2
2) are complementarily increased and decreased, which follows as
a corollary to the tridiagonal matrix diagonalization method of solution, for chosen values of `
and species AB of the polynomials. Section 4 identifies the shifting actions of the Lˆx, Lˆy and Lˆz
operators on the individual Lame´ polynomials of species A and B, respectively, and on their
matched products of species AB for each fixed value of `. Section 5 identifies the correspond-
ing actions of the pˆx, pˆy and pˆz operators on an initial harmonic polynomial `AB, raising and
lowering the angular momentum by one unit `′ = ` ± 1 into final polynomials `′A′B′ of oppo-
site parity and different species. Section 6 discusses the main results of this work, including
relationships among the spheroconal harmonics in the three levels of the identified operators,
as well as connections with other works in the literature.
2 Eigenvalues and eigenfunctions of Lˆ2 and Hˆ∗
Kramers and Ittmann [6] pioneered the quantum mechanical study of the rotations of asymmetric
molecules using spheroconal coordinates, showing the separability of the eigenvalue equations
for the square of the angular momentum and the complete Hamiltonian
Hˆ =
1
2
(
Lˆ2x
I1
+
Lˆ2y
I2
+
Lˆ2z
I3
)
(1)
in the body-fixed frame with principal axes, involving the moments of inertia I1 ≤ I2 ≤ I3. The
separated equations are of the Lame´ type, and its polynomial solutions are exact in principle,
but could not be numerically implemented for higher excited states at that time. Consequently,
the study of the rotations of asymmetric molecules developed along the perturbation theory
route taking the symmetric prolate and oblate molecule spherical harmonic solutions as the
non-perturbed starting point [7, 8, 16, 29, 35].
Patera and Winternitz used an alternative energy operator
E = −4
(
Lˆ21 + rLˆ
2
2
)
, 0 < r < 1,
in their work [24]. On the other hand, Pin˜a [27] and Valde´z and Pin˜a [32] used the alternative
parametrization of the original Hamiltonian of equation (1), in the form
Hˆ =
1
2
QLˆ2 +
1
2
P
(
e1Lˆ
2
x + e2Lˆ
2
y + e3Lˆ
2
z
)
,
where
Q =
1
3
(
1
I1
+
1
I2
+
1
I3
)
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 3
is the average of the three inverses of the moments of inertia characterizing a spherical top,
P 2 =
2
9
[(
1
I1
−
1
I2
)2
+
(
1
I1
−
1
I3
)2
+
(
1
I2
−
1
I3
)2
]
measures the magnitude of the asymmetry of the molecule and
Hˆ∗ =
1
2
(
e1L
2
x + e2L
2
y + e3L
2
z
)
(2)
is the asymmetry distribution Hamiltonian, with parameters e1, e1 and e3 such that
e1 ≥ e2 ≥ e3, e1 + e2 + e3 = 0, e
2
1 + e
2
2 + e
2
3 =
3
2
. (3)
The inequalities follow from those for the moments of inertia, the vanishing of their sum
reflects the zero trace of the matrix of the inverses of the moments of inertia after the term in Q
is separated, and the coefficient in P 2 and the sums of the squares are correlated. Only one of
the parameters ei is independent, the set of I1, I2, I3 being replaced by Q, P , ei.
Both of our works [9, 10] used the parametrizations of equations (2) and (3) with a single
independent parameter ei, in analogy with that in equation (1). At that time we were not aware
of [24]. Not surprisingly, their equivalence can be established and our respective methodologies
also overlap. In fact, our solution using the spherical canonical bases to construct the matrix
representation of Hˆ∗ and determine its eigenvalues and eigenfunctions by diagonalization [10] is
related to Sections 2 and 3 in [24]. On the other hand, our construction of the Lame´ eigenvalues
and polynomials also by diagonalization of the matrices representing the recurrence relations
for the series expansions in the Jacobi elliptic function representation of the spheroconal coor-
dinates [10], has as well points of contact with parts of Section 6 in [24]. We have just become
aware of some additional references [13, 15] and [14] of that period, whose titles describe the
overlap with this contribution. Specifically, the role of the D2 group of rotations by pi around
the cartesian coordinate axes as a finite symmetry group is explicitly recognized in [25] as the
missing ingredient for the complete characterization of the different species of Lame´ spheroconal
harmonics.
We refer the reader to [10, 27, 32] for the details or equations in what follows. The transfor-
mation equations between spheroconal and cartesian coordinates are
x = r dn
(
χ1|k
2
1
)
sn
(
χ2|k
2
2
)
, y = r cn
(
χ1|k
2
1
)
cn
(
χ2|k
2
2
)
,
z = r sn
(
χ1|k
2
1
)
dn
(
χ2|k
2
2
)
(4)
in terms of Jacobi elliptic functions sn
(
χ|k2i
)
, cn
(
χ|k2i
)
and dn
(
χ|k2i
)
with matching parameters
k21 + k
2
2 = 1 [1, 20]. The elliptic functions are related as
cn2
(
χ|k2
)
= 1− sn2
(
χ|k2
)
, dn2
(
χ|k2
)
= 1− k2 sn2
(
χ|k2
)
, (5)
and their derivatives are
d
dχ
sn
(
χ|k2
)
= cn
(
χ|k2
)
dn
(
χ|k2
)
,
d
dχ
cn
(
χ|k2
)
= − sn
(
χ|k2
)
dn
(
χ|k2
)
,
d
dχ
dn
(
χ|k2
)
= −k2 sn
(
χ|k2
)
cn
(
χ|k2
)
. (6)
The transformation equations (4) and equations (5) allow the identification of r as the radial
spherical coordinate, χ1 as an elliptical cone coordinate with axis along the x-axis and χ2 as an
elliptical cone coordinate with axis along z-axis. Their respective domains are −pi < am(χi) < pi
4 R. Me´ndez-Fragoso and E. Ley-Koo
and −pi/2 < am(χj) < pi/2 for k2i > k
2
j . Since k
2
1 is always associated with variable χ1 and k
2
2
with χ2, from now on in this manuscript, we simplify the notation as
(
χi|k2i
)
→ (χi), for the
sake of space saving.
The transformation equations (4) and the equations (6) lead in turn to the scale factors
hr = 1, hχ = hχ1 = hχ2 = r
√
1− k21 sn
2(χ1)− k22 sn
2(χ2) (7)
and to the Laplace operator
∇2 =
1
r2
∂
∂r
(
r2
∂
∂r
)
+
1
h2χ
(
∂2
∂χ21
+
∂2
∂χ22
)
.
From the latter the identification of the square of the angular momentum is immediate:
Lˆ2 = −
~2r2
h2χ
(
∂2
∂χ21
+
∂2
∂χ22
)
. (8)
The cartesian components of the angular momentum vector itself can be found in the Appen-
dix of [10], and allow the construction of the explicit form of the asymmetry distribution Hamil-
tonian
Hˆ∗ = −
~2r2
2h2χ
(
(
e1 − (e1 − e2) sn
2(χ2)
) ∂2
∂χ21
+
(
e3 − (e2 − e3) sn
2(χ2)
) ∂2
∂χ22
)
. (9)
Since Lˆ2 commutes with Hˆ∗, as easily tested using equation (2), both operators admit common
eigenfunctions with the factorizable form
Ψ(χ1, χ2) = Λ(χ1)Λ(χ2) (10)
for which the eigenvalue equations of the operators of equation (8) and (9), with eigenvalues
`(`+ 1) and E∗ become separable. Indeed by using the angular scale factors of equation (7), the
separability can be accomplished provided the geometric parameters in equations (4) and the
dynamic parameters in equation (9) are connected by
k21 =
e2 − e3
e1 − e3
, k22 =
e1 − e2
e1 − e3
.
This means that the specific spheroconal coordinate system is tailored to the asymmetry distri-
bution of the molecule.
The next result is that each of the factors in equation (10) satisfies the Lame´ equation
[21, 33, 34]
[
−
d2
dχ2i
+ `(`+ 1)k2i sn
2(χi)
]
Λi(χi) = hiΛi(χi) (11)
for i = 1, 2, with the respective eigenvalues
h1 = −
`(`+ 1)e3
e1 − e3
+
2E∗
e1 − e3
, h2 =
`(`+ 1)e1
e1 − e3
−
2E∗
e1 − e3
. (12)
Their combinations
h1 + h2 = `(`+ 1), e1h1 + e3h2 = 2E
∗, (13)
provide the eigenvalues of Lˆ2 and Hˆ∗, respectively.
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 5
Table 1. Matching Lame´ polynomials according to species and parities.
A 1 d c s dc ds cs dcs
B 1 s c d sc sd cd scd
AB 1 x y z xy xz yz xyz
Πx + − + + − − + −
Πy + + − + − + − −
Πz + + + − + − − −
Next, the solutions of the Lame´ equation (11) are also reviewed. The derivative equations (6)
for the elliptic functions, represented by their initial letters allow the identification of 1, s, c,
d, dc, ds, sc, dcs as removable singularity factors in the differential equation. The dependence
of both operators Lˆ2 and Hˆ∗ on the squares of Lˆx, Lˆy and Lˆz guarantee that their common
eigenfunctions, equation (10), have definite inversion parities under x→ −x, y → −y, z → −z.
Correspondingly, the Lame´ functions get classified into two kinds, each with four species sharing
the same number of even or odd factors in the removable singularity factors. The Lame´ functions
in the respective elliptic cone coordinates χ1 and χ2 in equation (10) must be matched according
to their singularity factors A(χ1) and B(χ2), and the respective parities from equations (4), as
illustrated in Table 1.
There are two kinds of Lame´ spheroconal harmonic functions distinguished by their over-
all parity (−)` = ΠxΠyΠz. For each value of ` each kind may contain four different species
characterized by the respective singularity factors.
The solutions of the Lame´ differential equation (11) have the general form
ΛA(χi) = A(χi)
NAmax∑
s=0
aAs sn
2s(χi). (14)
as a series of even-power of the elliptical sn(χi) function, where the expansion coefficients
satisfy three-term recurrence relations, which the interested reader may see in equations (32)–
(39) of [10], for the eight different species A. For the lower ` eigenstates the eigenvalues hA
(
k2i
)
and ratios of the expansion coefficients aAs /a
A
0 can be evaluated in a straightforward way from
equation (11), and the linear independence of the powers of sn(χi). The corresponding results
are illustrated in Table 2 for the individual Lame´ polynomials and in Table 3 for the matched
spheroconal harmonics.
For higher values of ` it is more practical to cast the recurrence relations into eigenvalue
problem matrix forms and to obtain from their diagonalizations the respective eigenvalues and
expansion coefficients. The sizes of the matrices are as follows for ` even:
N1max =
`
2
+ 1 and N scmax = N
sd
max = N
cd
max =
`
2
,
and for ` odd:
N smax = N
c
max = N
d
max =
`+ 1
2
and N scdmax =
`− 1
2
.
In both cases the total dimensions are 2` + 1, corresponding to the number of independent
spheroconal harmonic polynomials for each value of `. For each species there are NAmax different
eigenvalues which can be ordered according to their increasing values
hA1 < h
A
2 < h
A
3 < · · · < h
A
i < · · · < h
A
NAmax−1
< hANAmax , (15)
6 R. Me´ndez-Fragoso and E. Ley-Koo
or their decreasing values
hBNmax > h
B
Nmax−1 > · · · > h
B
j > · · · > h
B
3 > h
B
2 > h
B
1 . (16)
Obviously, the expansion coefficients in equation (14) depend on the specific eigenvalues as(hAi ),
as(hBj ). The first of equations (13) suggests the matching of the smaller eigenvalues of one
species with the larger ones of the companion species for the construction of the complete set of
spheroconal harmonics `ABij.
Let us also analyze the number of nodes in the respective factors of Lame´ functions in equa-
tion (14), nA and np. For the singularity removing factors their specific values are as follows:
n1 = nd = 0, nc = 0 or 1, ns = 1,
ndc = 0 or 1, nds = 1, ncs = 1 or 2, ndcs = 1 or 2. (17)
The polynomial of degree 2NAmax in sn(χ) has at the most N
A
max zeros sn
2(χp), appearing by
pairs with opposite signs ± sn(χp) with the possible numbers
np = 0, 2, 4, . . . , 2(Nmax − 1) (18)
counting the symmetric sheets of the nodal elliptical cones.
Therefore, the total number of nodes for Λ`An1 (χ1) Lame´ polynomial is
n1 = n
A + np = 0, 1, 2, . . . , ` (19)
and likewise for its matching companion Λ`Bn2 (χ2)
n2 = n
B + np = 0, 1, 2, . . . , `. (20)
Correspondingly, the spheroconal harmonic functions from the product of the pairs of matched
Lame´ polynomials exhibit the possible numbers
nA + nB = 0, 1, 2, 3 (21)
counting the shared nodal cartesian planes, as limiting cases of nodal elliptical cones, for the
respective species
AB = 1;x, y, z;xy, xz, yz;xyz.
In turn,
n1 + n2 = ` (22)
counts the total number of nodes characterizing any harmonic function of order `.
The ordering indices i, j for the eigenvalues in equations (15) and (16) can be replaced with
the quantum numbers n1 and n2. This is completely justified by recognizing that the eigenvalues
with matching quantum numbers, according to equation (22), are also matched to satisfy
h`An1 + h
`B
n2 = `(`+ 1) (23)
as required by equation (13).
Table 2 illustrates the eigenvalues h`Ani of the Lame´ functions for the successive values of
` = 0, 1, 2, . . . , and the respective species with the singularity removing factors. The eigenvalues
and their quantum numbers n1 = 0, 1, 2, . . . are listed in increasing order. The associated
polynomial factors in the eigenfunctions, equation (14), are also included.
Table 3 illustrates the matching of Lame´ eigenvalues and polynomials to obtain the sphero-
conal harmonics `ABn1n2 and their eigenenergies 2E∗ from equation (13), written in terms of
the asymmetry distribution parameter ei. The readers may check the ordering of the individual
Lame´ eigenvalues, correlated with the increasing of the number of nodes in the polynomials in
Table 2. The matching according to equations (22) and (23), and the ordering of increasing
energies can be appreciated in Table 3.
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 7
Table 2. Lame´ eigenvalues h`An1 and polynomials.
A hAni Polynomial
` = 0 1 h10 = 0 1
` = 1 d hd0 = k
2
i 1
c hc1 = 1 1
s hs1 = 1 + k
2
i 1
` = 2 dc hdc1 = 1 + k
2
i 1
ds hds1 = 1 + 4k
2
i 1
cs hcs2 = 4 + k
2
i 1
1 h10 = 2(1 + k
2
i )− 2
√
1− k2i (1− k
2
i ) 1−
h10
2 sn
2(χi)
1 h12 = 2(1 + k
2
i ) + 2
√
1− k2i (1− k
2
i ) 1−
h12
2 sn
2(χi)
` = 3 dcs hdcs2 = 4(1 + k
2
i ) 1
d hd0 = (5k
2
i + 2)− 2
√
4k4i − k
2
i + 1 1 +
k2i−h
d
0
2 sn
2(χi)
d hd2 = (5k
2
i + 2) + 2
√
4k4i − k
2
i + 1 1 +
k2i−h
d
2
2 sn
2(χi)
c hc1 = (5 + 2k
2
i )− 2
√
4− k2i (1− k
2
i ) 1 +
1−hc1
2 sn
2(χi)
c hc3 = (5 + 2k
2
i ) + 2
√
4− k2i (1− k
2
i ) 1 +
1−hc3
2 sn
2(χi)
s hs1 = 5(1 + k
2
i )− 2
√
4k4i − 7k
2
i + 4 1 +
1+k2i−h
s
1
6 sn
2(χi)
s hs3 = 5(1 + k
2
i ) + 2
√
4k4i − 7k
2
i + 4 1 +
1+k2i−h
s
3
6 sn
2(χi)
` = 4 1 h3 − 20(1 + k2i )h
2 1 + a1a0 sn
2(χi) +
a2
a0
sn4(χi)
+ [64(1 + k2i ) + 208k
2
i ]h a1 = −
h1ni
2 a0; a2 =
7k2i h
1
ni
16(1+k2i )−h
1
ni
a0
− 640k2i (1 + k
2
i ) = 0 The roots of the polynomial
are h10, h
1
2, h
1
4
dc hdc1 = 5(1 + k
2
i )− 2
√
4 + k2i + 4k
4
i 1−
hdc1 −(1+k
2
i )
2 sn
2(χi)
dc hdc3 = 5(1 + k
2
i ) + 2
√
4 + k2i + 4k
4
i 1−
hdc3 −(1+k
2
i )
2 sn
2(χi)
ds hds1 = 5(1 + 2k
2
i )− 2
√
4− 9k2i (1− k
2
i ) 1−
hds1 −(1+4k
2
i )
6 sn
2(χi)
ds hds3 = 5(1 + 2k
2
i ) + 2
√
4− 9k2i (1− k
2
i ) 1−
hds3 −(1+4k
2
i )
6 sn
2(χi)
cs hcs2 = 5(2 + k
2
i )− 2
√
9− 9k2i + 4k
4
i 1−
hcs2 −(4+k
2
i )
6 sn
2(χi)
cs hcs4 = 5(2 + k
2
i ) + 2
√
9− 9k2i + 4k
4
i 1−
hcs4 −(4+k
2
i )
6 sn
2(χi)
3 Raising and lowering of quantum numbers n1 and n2
for spheroconal harmonic polynomials of a chosen kind
and species `ABn1n2
The spheroconal harmonic polynomials with their labels for angular momentum `, species AB
and number of nodes n1 and n2 can be written as the products of the pairs of matching Lame´
polynomials
Ψ`ABn1n2
(
χ1, χ2;h
`A
n1 , h
`B
n2
)
= Λ`An1
(
χ1, h
`A
n1
)
Λ`Bn2
(
χ2, h
`B
n2
)
, (24)
Λ`An1
(
χ1, h
`A
n1
)
= A(χ1)a
A
0
(
h`An1
)
Nmax∑
s=0
a¯As
(
h`An1
)
sn2s(χ1) (25)
8 R. Me´ndez-Fragoso and E. Ley-Koo
Table 3. Eigenenergies 2E∗ in units of ~2 for Lame´ spheroconal harmonics `ABn1n2.
A B n1 n2 2E∗
` = 0 1 1 0 0 0
` = 1 d s 0 1 −e1
c c 1 0 −e2
s d 1 0 −e3
` = 2 1 1 0 2 −3
dc sc 1 1 3e3
ds sd 1 1 3e2
cs cd 2 0 3e1
1 1 2 0 3
` = 3 d s 0 3 −3e1 − 3
√
5− 4e21
c c 1 2 −3e2 − 3
√
5− 4e22
s d 1 2 −3e3 − 3
√
5− 4e23
dcs scd 2 1 0
d s 2 1 −3e1 + 3
√
5− 4e21
c c 3 0 −3e2 + 3
√
5− 4e22
s d 3 0 −3e3 + 3
√
5− 4e23
` = 4 1 1 0 4 e1h10(k
2
1) + e3h
1
4(k
2
2)
dc sc 1 3 5e3 −
√
21 + 60e23
ds sd 1 3 5e2 −
√
21 + 60e22
cs cd 2 2 5e1 −
√
21 + 60e21
1 1 2 2 e1h12(k
2
1) + e3h
1
2(k
2
2)
dc sc 3 1 5e3 +
√
21 + 60e23
ds sd 3 1 5e2 +
√
21 + 60e22
cs cd 4 0 5e1 +
√
21 + 60e21
1 1 4 0 e1h14(k
2
1) + e3h
1
0(k
2
2)
factorizing the zero power coefficients aA0
(
h`An1
)
and using the ratio of coefficients for the other
powers
a¯As
(
h`An1
)
=
aAs
(
h`An1
)
aA0
(
h`An1
) (26)
and similarly for its companion with A→ B and n1 → n2. As established in the previous section,
equations (22) and (23) define the matching of quantum numbers and eigenvalues, respectively.
For chosen values of `, A and B, the removed singularity nodes are fixed in numbers nA
and nB, according to equations (17)–(21). Then according to equations (18)–(20) the number
of nodes np, n1 and n2 change in steps of 2. the inequalities in equations (15) and (16) for the
increasing and decreasing eigenvalues become
h`AnA < h
`A
nA+2 < · · · < h
`A
n1−2 < h
`A
n1 < h
`A
n1+2 < · · · < h
`A
`−nB−2 < h
`A
`−nB , (27)
and
h`B`−nA > h
`B
`−nA−2 > · · · > h
`B
n2+2 > h
`B
n2 > h
`B
n2−2 > · · · > h
`B
nB+2 > h
`B
nB . (28)
If we start from the state `ABn1n2 of equation (24) depending on the eigenvalues appearing
in the middle of equations (27) and (28), the state involving their neighbors to the right have
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 9
raised n1 by two units and lowered n2 by two units with the corresponding change in the
eigenvalues which remain satisfying matching conditions of equations (22) and (23); the same
changes operate in equations (25) and (26) for the eigenfunctions via the eigenvalue dependence
of the expansion coefficients. Similarly, if we had moved to the neighbors on the left: n1 → n1−2
and n2 → n1 + 2 with the complementary lowering and raising by two, with their consequences
in the changes in the matching eigenvalues and the other state of the same species. Obviously,
the lowering and raising actions can be extended to the right and left ends of equations (27)
and (28) covering all the NAmax = N
B
max states of the `AB species. Examples of these connections
can be found in Tables 2 and 3.
As a prelude to the following two sections we include a couple of purely spheroconal coordinate
tools. The first one illustrates the successive species changing actions of the derivative operator
on the singularity removing factors and even-power polynomials appearing in the process:
∂
∂χi
∂2
∂χ2i
1 0 0
s cd (−k2i c
2 − d2)s
c −sd (−k2i s
2 + d2)c
d −k2i sc −k
2
i (c
2 − s2)d
cd (−k2i c
2 − d2)s (−k2i c
2 − d2 + 2k2i s
2)cd
sd (−k2i s
2 + c2)c (k2i s
2 − d2 − 2k2i c
2)sd
sc (s2 − c2)d (−k2i s
2 + k2i c
2 + 2k2i d
2)sc
scd −k2c2s2 − d2s2 + d2c2 2[k2i (s
2 − c2) + (k2i s
2 − d2)− (k2i c
2 + d2)]scd
s2, c2, d2 2scd (1,−1,−k2i )
The first derivative causes changes of species with one factor to species with the other two
factors and viceversa. The species 1 is represented by the top entry, and also by the bottom
one; and species dcs and 1 are also connected by their first derivatives as illustrated by the two
bottom entries. The second derivative returns each species to the original one. The even-power
polynomials can be reduced to polynomials in sn2(χ) via equation (5).
The second tool is connected with equation (25), expressing the set of Lame´ polynomials `An1
as a linear combination of the A(χ) sn2s(χ) basis. Both bases have the same dimension NAmax+1,
and the members of the latter can be expressed as linear combinations of Lame´ polynomials.
The transformation coefficients a¯A invs ni are the elements of the inverse matrix of a¯
A
s (h
`A
n1 ).
4 Angular momentum cartesian components connecting pairs
of polynomials of the four different species with a common
eigenvalue `
The explicit expressions for the cartesian components of the angular momentum operators in
spheroconal coordinates are borrowed as equations (A15)–(A17) in [10]:
Lˆx =
−i~r2
h2χ
[
dn(χ1) cn(χ2) dn(χ2)
∂
∂χ1
+ k21 sn(χ1) cn(χ1) sn(χ2)
∂
∂χ2
]
, (29)
Lˆy =
−i~r2
h2χ
[
−cn(χ1) sn(χ2) dn(χ2)
∂
∂χ1
+ sn(χ1) dn(χ1) cn(χ2)
∂
∂χ2
]
, (30)
Lˆz =
−i~r2
h2χ
[
−k22 sn(χ1) sn(χ2) cn(χ2)
∂
∂χ1
− cn(χ1) dn(χ1) dn(χ2)
∂
∂χ2
]
. (31)
10 R. Me´ndez-Fragoso and E. Ley-Koo
Table 4. Eigenfunctions with ` = 1 and its resulting application of each cartesian angular momentum
operator.
Lˆx Lˆy Lˆz
Λd0Λ
s
1 0 −Λ
s
1Λ
d
0 Λ
c
1Λ
c
0
Λc1Λ
c
0 Λ
s
1Λ
d
0 0 −Λ
d
0Λ
s
1
Λs1Λ
d
0 −Λ
c
1Λ
c
0 Λ
d
0Λ
s
1 0
This section evaluates the actions of these operators on the lower `ABn1n2 spheroconal
harmonic polynomials of the same kind for a fixed value of `, connecting with different species
`A′B′n′1n
′
2.
The calculations are straightforward requiring care, labor and some guidelines. The deriva-
tives ∂/∂χi act only on the first or second factor in equation (24) for i = 1 or 2. The individual
changes of species were already described in the first tool of the prelude, and for an initial mat-
ching species AB the final ones A′B′ follow. Notice the appearance of the square of the angular
scale factor in the three operators in equations (29)–(31). This requires that the application of
the operators inside the brackets to the spheroconal harmonic polynomials provides the A′B′
factor and also the h2χ/r
2 factor to compensate the one in the previous line. This requirement is
indeed satisfied. The remaining factor can be reduced to a polynomial in even-powers of sn2(χ1)
and sn2(χ2), up to NA
′
max = N
B′
max, respectively. The remaining task is to identify the harmonic
linear superposition of the polynomials, making use of the linear independence and complete-
ness of both bases in the second tool of the prelude. Some of our results on the actions of Lˆx,
Lˆy, Lˆz on the non-normalized spheroconal harmonic polynomials `ABn1n2 for ` = 0, 1, 2, 3 are
illustrated and described next. The application of any of the operators Lˆi on the Λ10Λ
1
0 = 1 leads
to the same single eigenstate with its eigenvalue zero.
Table 4 exhibits the result of the corresponding applications on the three spheroconal harmo-
nics with ` = 1. The contents in the table should not be surprising upon recognizing the species x,
y, z of the successive monomials, and their equivalence with the respective cartesian harmonics.
Table 5 for the ` = 2 polynomials contains familiar information for the unique monomial
species xy, xz and yz transforming among themselves under the respective rotations, with
coefficients one in the corresponding entries. The two Λ10Λ
1
2 and Λ
1
2Λ
1
0 binomial companions get
transformed into the monomials of the other species as illustrated by the top and bottom rows
in the table, with coefficients involving the eigenvalues h1n1(k
2
1) and h
1
n2(k
2
2) of the matching
binomials; the respective species of the monomials are complementary to that of the operators,
as the reader can ascertain by moving along the top and bottom rows in the successive columns.
In turn, the respective operators acting on the monomials lead to the linear superpositions of
the two Λ1n1Λ
1
n2 binomials with more elaborate coefficients including the common one C
1
C14,1 =
−2a¯s1(h
s
3(k
2
2)) + a¯
d
1(h
d
0(k
2
1))
a¯d1(h
d
2(k
2
1))a¯
s
1(h
s
3(k
2
2))− a¯
d
1(h
c
0(k
2
1))a¯
s
1(h
s
1(k
2
2))
, C24,1 = 1− C
1
4,1 (32)
C14,3 = C
1
4,1 (by changing d→ s), C
2
4,3 = −
(
1 + C14,3
)
, (33)
C14,2 = −C
2
4,2 =
a¯c1(h
c
2(k
2
2)) + a¯
c
1(h
c
1(k
2
1))
a¯c1(h
c
3(k
2
1))a¯
c
1(h
c
2(k
2
2))− a¯
c
1(h
c
1(k
2
1))a¯
c
1(h
c
0(k
2
2))
. (34)
The spheroconal harmonics with ` = 3 come in a single monomial of species [dcs][scd] =
[xyz] and three pairs of binomials of species x, y and z. The monomial appears in the middle
row of Table 6, and its companions of the other species in the rows below and above. The
monomial transformed into the x, y, z species in the successive columns by the respective
angular momentum components; the transformed states are linear combinations of the pair of
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 11
Table 5. Eigenfunctions with ` = 2 and its resulting application of each cartesian angular momentum
operator. The common factor in the table has the value C1 =
[
h10(k
2
1)− h
1
2(k
2
1)
]−1
.
Lˆx Lˆy Lˆz
Λ10Λ
1
2 −h
1
0(k
2
1)Λ
cs
2 Λ
cd
0 (h
1
0(k
2
1)− h
1
2(k
2
2))Λ
ds
1 Λ
sd
1 h
1
2(k
2
2)Λ
dc
1 Λ
sc
1
Λdc1 Λ
sc
1 Λ
ds
1 Λ
sd
1 −Λ
cs
2 Λ
cd
0 C
1
(
(2− h10(k
2
1))Λ
1
2Λ
1
0 −
(2− h12(k
2
1))Λ
1
0Λ
1
2
)
Λds1 Λ
sd
1 −Λ
dc
1 Λ
sc
1 2C
1
(
Λ12Λ
1
0
− Λ10Λ
1
2
)
Λcs2 Λ
cd
0
Λcs2 Λ
cd
0 C
1
(
(2− h12(k
2
2))Λ
1
2Λ
1
0 −
(2− h10(k
2
2))Λ
1
0Λ
1
2
)
Λdc1 Λ
sc
1 −Λ
ds
1 Λ
sd
1
Λ12Λ
1
0 −h
1
2(k
2
1)Λ
cs
2 Λ
cd
0 (h
1
2(k
2
1)− h
1
0(k
2
2))Λ
ds
1 Λ
sd
1 h
1
0(k
2
2)Λ
dc
1 Λ
sc
1
Table 6. Eigenfunctions with ` = 3 and its resulting application of each cartesian angular momentum
operator. The element Cki,j represents the k coefficient of the linear combination at the i row and j
column of the table. Some examples are represented in the equations (32)–(34).
Lˆx Lˆy Lˆz
Λd0Λ
s
3 2a¯
d
1
(
hd0(k
2
1)
)
Λdcs2 Λ
scd
1 C
1
1,2Λ
s
1Λ
d
2 + C
2
1,2Λ
s
3Λ
d
0 C
1
1,3Λ
c
1Λ
c
2 + C
2
1,3Λ
c
3Λ
c
0
Λc1Λ
c
2 C
1
2,1Λ
s
1Λ
d
2 + C
2
2,1Λ
s
3Λ
d
0 (h
c
1(k
2
1)− h
c
2(k
2
2))Λ
dcs
2 Λ
scd
1 C
1
2,3Λ
d
0Λ
s
3 + C
2
2,3Λ
d
2Λ
s
1
Λs1Λ
d
2 C
1
3,1Λ
c
1Λ
c
2 + C
2
3,1Λ
c
3Λ
c
0 C
1
3,2Λ
d
0Λ
s
3 + C
2
3,2Λ
d
2Λ
s
1 −2a¯
d
1
(
hd2(k
2
2)
)
Λdcs2 Λ
scd
1
Λdcs2 Λ
scd
1 C
1
4,1Λ
d
0Λ
s
3 + C
2
4,1Λ
d
2Λ
s
1 C
1
4,2Λ
c
1Λ
c
2 + C
2
4,2Λ
c
3Λ
c
0 C
1
4,3Λ
s
1Λ
d
2 + C
2
4,3Λ
s
3Λ
d
0
Λd2Λ
s
1 2a¯
d
1
(
hd2(k
2
1)
)
Λdcs2 Λ
scd
1 C
1
5,2Λ
s
1Λ
d
2 + C
2
5,2Λ
s
3Λ
d
0 C
1
5,3Λ
c
1Λ
c
2 + C
2
5,3Λ
c
3Λ
c
0
Λc3Λ
c
0 C
1
6,1Λ
s
1Λ
d
2 + C
2
6,1Λ
s
3Λ
d
0 (h
c
3(k
2
1)− h
c
0(k
2
2))Λ
dcs
2 Λ
scd
1 C
1
6,3Λ
d
0Λ
s
3 + C
2
6,3Λ
d
2Λ
s
1
Λs3Λ
d
0 C
1
7,1Λ
c
1Λ
c
2 + C
2
7,1Λ
c
3Λ
c
0 C
1
7,2Λ
d
0Λ
s
3 + C
2
7,2Λ
d
2Λ
s
1 2a¯
d
1
(
hd0(k
2
2)
)
Λdcs2 Λ
scd
1
companion binomials with different number of nodes n1 and n2. The inverse transformations
of the successive binomials leading back to the single monomial are identified in the row and
column positions (1, 1), (2, 2), (3, 3), (5, 1), (6, 2) and (7, 3). The individual binomial spheroconal
harmonics are transformed also into linear combinations of the pairs of binomials of species
complementary to the component of the angular momentum, as an inspection of the remaining
twelve positions in the table show. The coefficients involved become more numerous, taking
into account the increasing number of the states and their combinations.
We complement this section with the following diagrams in Fig. 1 sketching the connections
among the four species, for the two kinds of even and odd ` of spheroconal harmonics, provided
by the angular momentum components. The interested readers may compare them with their
counterparts in [24]. The coefficients in the entries of Tables 4–6 are the counterpart of the
raising and lowering operator coefficients for the spherical harmonics.
ˆ
L
x
ˆ
L
z
x
y
z
xyz
ˆ
L
x
ˆ
L
z
ˆ
L
x
yz
x z
x y
1
ˆ
L
x
ˆ
L
z
ˆ
L
z
ˆ
L
y
ˆ
L
y
Figure 1. Action of the angular momentum operators on each of the spheroconal harmonics.
12 R. Me´ndez-Fragoso and E. Ley-Koo
5 Linear momentum cartesian components raising and lowering
the angular momentum by one unit between polynomials
of opposite parities
The cartesian components of the linear momentum operator in spheroconal coordinates are
pˆx = dn(χ1) sn(χ2)pˆr−
i~r
h2χ
[
−k21 sn(χ1) cn(χ1) sn(χ2)
∂
∂χ1
+ dn(χ1) cn(χ2) dn(χ2)
∂
∂χ2
]
, (35)
pˆy = cn(χ1) cn(χ2)pˆr −
i~r
h2χ
[
− sn(χ1) dn(χ1) cn(χ2)
∂
∂χ1
− cn(χ1) sn(χ2) dn(χ2)
∂
∂χ2
]
, (36)
pˆz = sn(χ1) dn(χ2)pˆr −
i~r
h2χ
[
cn(χ1) dn(χ1) dn(χ2)
∂
∂χ1
− k22 sn(χ1) sn(χ2) cn(χ2)
∂
∂χ2
]
. (37)
Notice that the angular factors of pˆr are simply the projections of the unit radial vector along
the respective axes, equation (4). The angular factor of the derivatives inside the brackets in
equations (29)–(31) and (35)–(37) for the successive components are the same but in exchanged
positions, and different signs in some cases. The reason for this is found in the decomposition
of the ~p vector into its radial and transverse components
~ˆp = rˆpˆr − ~r ×
~ˆL
r
. (38)
already used in [18]. Correspondingly, also notice the presence of the factor r/h2χ in equa-
tions (35)–(37). The actions of these on a spheroconal harmonic functions `ABn1n2 lead to
functions of the other kind `′A′B′n′1n
′
2 with `
′ = `± 1, species A′B′ with the other parity. Con-
sequently, the method and some of the steps and results of the previous section are useful or have
their counterparts in the application of the operators of equations (35)–(37) on the spheroconal
harmonic polynomials `ABn1n2.
At the level of each individual spheroconal coordinate, the multiplications by d, c, and s
of the first terms in the operators in equations (35)–(37) with the eight species of singularity
removing factors A(χ) lead to the following result:
1 s c d cd sd sc scd
d d ds dc d2 cd2 sd2 scd scd2
c c cs c2 cd c2d scd sc2 sc2d
s s s2 sc sd scd s2d s2c s2cd
with the common result that every original A(χ) is changed in kind and species. The effects
are qualitatively similar and complementary to those of the first derivative in the table of the
prelude at the end of Section 3. In fact, the union of both tables provides the sets of four species
associated with the other kind of Lame´ functions.
What has been said for A(χ1) also holds for the companion B(χ2), and the resulting A′(χ1)
and B′(χ2) can be properly matched. At the level of multiplication in the first terms of
equations (35)–(37), their respective x, y and z character has already been recognized. As
a consequence of the exchange of angular factors in the derivative terms in equations (29)–(31)
and (35)–(37), the kinds and species maintained in the previous section are changed in the
present one. The net result is that the angular derivative terms in equations (35)–(37) acting
on the individual Lame´ functions `An1 and `Bn2 transform them into the same kinds and
species A′(χ1), B′(χ2) obtained by multiplication in the respective first terms.
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 13
We proceed to analyze the effects of the operators of equations (35)–(37) on the successive
Lame´ spheroconal functions. For ` = 0, Λ10(χ1)Λ
1
0(χ2) = 1 is annihilated by the derivative terms,
and transformed into
dn(χ1) sn(χ2) = Λ
d
0(χ1)Λ
s
1(χ2) =
x
r
, cn(χ1) cn(χ2) = Λ
c
1(χ1)Λ
c
0(χ2) =
y
r
,
sn(χ1) dn(χ2) = Λ
s
1(χ1)Λ
d
0(χ2) =
z
r
,
respectively, by the multiplication operations. The identifications with the cartesian harmonics
is also made. Their angular momentum of ` = 1 and negative parity are also recognized in
contrast with the ` = 0 and positive parity of the original state.
Next, we illustrate the net result of the applying the derivative terms on the ` = 1 states,
reducing them by factoring the square of the scale factor, obtaining the following table of mono-
mials and binomials:
Table 7. Actions of angular derivative terms in pˆx, pˆy, pˆz on ` = 1 spheroconal harmonics.
pˆx pˆy pˆz
Λ1d0 Λ
1s
1 1− dn
2(χ1) sn2(χ2) Λ2dc1 Λ
2sc
1 Λ
2ds
1 Λ
2sd
1
Λ1c1 Λ
1c
0 Λ
2dc
1 Λ
2sc
1 1− cn
2(χ1) cn2(χ2) Λ2cs2 Λ
2cd
0
Λ1s1 Λ
1d
0 Λ
2ds
1 Λ
2sd
1 Λ
2cs
2 Λ
2cd
0 1− sn
2(χ1) dn2(χ2)
The off-diagonal entries are identified as Λ2dc1 (χ1)Λ
2sc
1 (χ2) = xy, Λ
2ds
1 (χ1)Λ
2sd
1 (χ2) = xz and
Λ2cs2 (χ1)Λ
2cd
0 (χ2) = yz obtained via two different operators acting on two different initial states.
They could also be obtained via the multiplication with the factors in the first terms of equa-
tions (35)–(36). The identification of their angular momentum ` = 2, and positive parity and
nodal quantum numbers can be made from Table 3.
The diagonal entries deserve additional analysis before the lowering effect of the operators
is identified, as well as the raising effects leading to the remaining two ` = 2 spheroconal
harmonics. The three entries have been obtained via three different operators acting on three
different initial functions. Of course, the “ones” correspond to the monopolar harmonic to which
we go back by the lowering effect on the dipole harmonics. On the other hand, the other terms
are identified as the squares of the projections of the radial unit vector along the coordinate
axes. Their sum is “one” coinciding again with the lowered ` = 0 state. Of the three terms,
only two are linearly independent, since their sum is fixed. This suggests that the three terms
can be combined in two linearly independent combinations to be identified with the missing
Λ210 (χ1)Λ
21
2 (χ2) and Λ
21
2 (χ1)Λ
21
0 (χ2), ` = 2 spheroconal harmonics.
The analysis can be made more transparent by recognizing that x2, y2 and z2 are equivalent
to them upon multiplication by r2. Let us consider the linear combination
Φ(x, y, z) = αx2 + βy2 + γz2. (39)
It is advantageous to choose it as harmonic
∇2Φ = 2α+ 2β + 2γ = 0, (40)
because in such a case we are sure that their connection with the spheroconal harmonics is
linear. In fact, from equation (40) we get
β = −α− γ,
and rewrite equation (39) in the separable form in spheroconal coordinates
Φ(r, χ1, χ2) = r
2 [α dn2(χ1) cn
2(χ2)− (α+ γ) cn
2(χ1) cn
2(χ2) + γ sn
2(χ1) dn
2(χ2)
]
. (41)
14 R. Me´ndez-Fragoso and E. Ley-Koo
The question to be answered is which values of the coefficients α and γ combining the diagonal
angular entries lead to the ` = 2 spheroconal harmonics of species 1 1.
The answers are obtained by rewriting equation (41) as polynomials in even-powers of sn(χ1)
and sn(χ2) and comparing them with the target polynomials from Table 2. Their explicit
forms are
α0 2 = −
1
2
+
1
4
h10
(
k21
)
−
1
4
h12
(
k22
)
, γ0 2 = −
1
2
−
1
4
h10
(
k21
)
+
1
4
h12
(
k22
)
,
and
α2 0 = −
1
2
+
1
4
h12
(
k21
)
−
1
4
h10
(
k22
)
, γ2 0 = −
1
2
−
1
4
h12
(
k21
)
+
1
4
h10
(
k22
)
,
defining the proportions of the presence of the respective spheroconal harmonics in the diagonal
entries in the Table 7. We remind the reader that the analysis has been made for non-normalized
polynomials. In any case, the coefficients above are the counterpart of the familiar spherical
Clebsch–Gordan coefficients. Work on the raising and lowering from ` = 2, 3, . . . is in process.
6 Discussion
Some of our works on the rotations of asymmetric molecules and the Lame´ spheroconal harmonics
have taken advantage of their connections with their spherical and cartesian counterparts [9, 18],
and others have been developed strictly within the spheroconal formalism [10, 17, 19, 18]. The
analysis and identification of the three sets of ladder operators in this article has been purpose-
fully implemented in the same formalism, avoiding the spherical and cartesian crutches.
The connections among Lame´ spheroconal polynomials of a given kind and species, and
different numbers of nodes have been explicitly recognized in Section 3. They share the same
form and degree, differing in their number of nodes ni; in contrast with the classical polynomials
having a number of nodes equal to their degree. For the spheroconal harmonics constructed by
the product of Lame´ polynomials with matching number of nodes and eigenvalues, equations (22)
and (23), their complete set is connected by their complementary raising of n1 and lowering of n2.
The inversion of equation (25) provides the basis of the powers of sn2(χ) as a linear combination
of the set of corresponding Lame´ polynomials, as the counterpart of the known relationships in
the classical polynomials.
Our other contribution in this volume of SIGMA [11] contains another example of polynomial
eigenfunctions, for the Hydrogen atom confined by a dihedral angle in prolate spheroidal coor-
dinates, evaluated by diagonalization of tridiagonal finite size matrices, and their connections
by complementary changes in the numbers of prolate spheroidal and hyperboloidal nodes.
The shifting actions of the Lˆx, Lˆy, Lˆz operators among the spheroconal harmonics of the four
species for a chosen value `, as illustrated in Tables 5 and 6, allow the generation of the corre-
sponding coefficients in the purely spheroconal formalism. They are the counterpart of the famil-
iar raising and lowering coefficients C±(`,m) for the spherical harmonics, and even closer for the
spherical harmonics with definite parities. The relationships so far are for the non-normalized
coefficients, but work is under way to identify and incorporate the normalization coefficients.
The ` raising and lowering actions of pˆx, pˆy and pˆz among spheroconal harmonics of neighbo-
ring kinds and species has been illustrated for the lower states, but the systematics had already
been recognized in [18]. While writing the latter, several works on related topics [12, 30, 31]
allowed us to recognize the complete radial and angular raising and lowering actions for the free
particle in spherical coordinates. Now we can also extend it to spheroconal coordinates.
Pin˜a identified four step ∆` = 4 ladder operators for spheroconal harmonics of the same
species for the most asymmetric molecules [26]. We are investigating their possible connection
Ladder Operators for Lame´ Spheroconal Harmonic Polynomials 15
with the application of the pˆi operators four times in succession leading to the same states. In
such a case the results are valid for any asymmetry distribution.
The familiarity with cartesian, spherical and spheroconal harmonics is decreasing when writ-
ten in this order. The works [9, 24] used the spherical basis as the tool to evaluate the spheroconal
harmonics. In the process the interbasis expansion coefficients are generated for the original
problem, and automatically also for the inverse problem. The specific example at the end of
Section 5 shows the spheroconal quadrupole composition of the cartesian one in equation (39).
As a complement to the comment in the third paragraph of this section, we include the
following related references with their respective comments. The contents in [2] for the free
Hydrogen atom in configuration space overlap with ours in [11], with emphasis on the rarely
treated spheroidal sets, and in the present contribution, on the properties of spheroelliptic or-
bitals, which have been so far practically ignored. The related work [3] also deals with the free
Hydrogen atom in momentum space focusing on the hyperspherical harmonic elliptic Sturmian
basis set in S3. The earlier work [5] deals with the free quantum motion on the three-dimensional
sphere S3 ellipso-cyllindrical coordinates, distinguishing between prolate and oblate elliptic co-
ordinates. On the other hand the more recent work [4] deals with the use of the hyperspherical
elliptic coordinates and harmonic basis sets in the fifth dimensional sphere S5 for the study
of the three-body problem in quantum mechanics. Its classical astronomical counterpart [28]
uses the relative radial coordinate of the first two particles and the radial coordinate of the
third particle relative to the center of mass of the first two, instead of the hyper-radius and
one of the five angular coordinates in S5. It is also pertinent to mention Sasaki’s contribution
in the Symposium, “Exactly solvable quantum mechanics and infinite families of multi-indexed
orthogonal polynomials”, and to cite [22, 23], involving Hamiltonians with tridiagonal matrix
representations. The raising and lowering operators in our Section 3 have their counterparts for
the respective eigenfunctions in the references of this paragraph.
Acknowledgements
The authors express their appreciation to the organizers of the Symposium and editors of this
Volume of SIGMA on “Superintegrability, Exact Solvability, and Special Functions” for their
invitations to participate in both. The authors acknowledge the financial support for this work
by Consejo Nacional de Ciencia y Tecnolog´ıa, SNI-1796.
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