Eur. Phys. J. D 12, 435-448 (2000)
https://doi.org/10.1007/s100530070005

A theoretical study of CO₂ and N₂0 molecules trapped in an argon matrix: Vibrational energies, and transition moments for low-lying levels and IR bar spectra

¹ Laboratoire d'Astrophysique de l'Observatoire de Besançon (UPRES A CNRS 6091), 41 bis avenue de l'Observatoire, B.P. 1615, Université de Franche-Comté, 25010 Besançon Cedex, France
² Laboratoire de Physique Moléculaire et Applications (UPR CNRS 136), Université P. et M. Curie, Tour 13, Boîte 76, 4 place Jussieu, 75252 Paris Cedex 05, France

Received: 22 March 2000
Revised: 10 May 2000
Published online: 15 December 2000

Abstract

Semi-empirical atom-atom potential energy calculations based on pairwise additive interactions are performed and, after applying the Born-Oppenheimer approximation to separate high frequency vibrational modes from low frequency orientational and translational modes, the infrared vibrational spectra of CO₂ and N₂O monomers trapped in an argon matrix at a temperature of 5 K are determined. It is shown that only a double substitutional site in argon can accommodate N₂O, whereas CO₂ is trapped in two distinct sites, of single and double substitutional types. The model shows that splitting of the degenerate ν2 mode occurs for both molecules in the double site. In the ground electronic state, the vibrational frequency shifts due to the matrix and the vibrational transition moments for low-lying levels are determined using the contact transformation method, as used for gas phase calculations. Calculated energy levels compare well with observed ones and the theory also predicts some unobserved levels. Moreover, calculations show no significant changes in the dipole moments of both CO₂ and N₂O trapped molecules.