Effect of stable and metastable dimers on collision-induced rototranslational spectra: Carbon dioxide - rare gas mixtures

- Manifestation of van der Waals dimers in collision-induced spectra is modeled.
- The dimer contribution is about a quarter of the contribution from 'ordinary' collisions.
- Metastable dimers play a significant role in collision-induced band formation.

The role of stable and metastable dimers as well as of free collisions in the collision-induced rototranslational absorption by the compressed CO2-Ar and CO2-Xe gas mixtures is elucidated using the classical three-dimensional trajectories method. The contribution from the stable dimers is obtained via Fourier transform of the dipole correlation function. The spectral bandshape due to the unbound trajectories (metastable dimers and free collisions) is calculated as an averaged Fourier spectrum of the collision-induced dipole moment. The mean lifetimes of metastable dimers have been estimated as 3.8 ps for CO2-Ar and 5.9 ps for CO2-Xe pairs. Trajectory computations are complemented by calculations of zero spectral moments using pair distribution functions. The stable and metastable dimer contribution to the zero spectral moment is shown to be comparable with that from free collisions.

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