The vibration-rotation of H₂O and its complexation with CO₂ in solid argon revisited

Abstract

Fourier-transform infrared spectroscopy in the frequency range 400–4000 cm–¹ has been used to investigate the absorption of H₂O and H₂O:CO₂ complex isolated in solid argon. Thanks to the lowest temperature reached in our experiment, temperature effects and nuclear spin conversion studies allow us to propose a new assignment of the rovibrational lines in the bending band n₂ for the quasi-freely rotating H₂O. An additional wide structure observed in this band shows two maxima around 1657.4 and 1661.3 cm–¹, with nuclear spin conversion of the high frequency part into the low frequency one. This structure is tentatively attributed to a rotation-ranslation coupling of the molecule in the cage. However, the equivalent effect is not observed in the vibrational stretching bands n₁ and n₃. Finally, by double doping experiments with CO₂, important new structures appear, leading us to unambiguously extract the frequencies of the lines of the H₂O:CO₂ complex.