Non-Markovian rotational relaxation matrix for fast collisions between two linear molecules in high-pressure gaseous media. I. General formalism and preliminary testing.

Collisional mixing of (vib)rotational lines appearing in spectroscopic signatures of dense planetary atmospheres and combustion environments is rigorously handled for the case of two linear colliders in terms of incomplete (non-Markovian) collisions related to off-energy-shell scattering amplitudes. Contrary to the standard impact-approximation approaches valid solely in band-centre regions, a new uniform broadband spectrum description is developed on the basis of a frequency-dependent rotational relaxation matrix which accurately accounts for the influence of the extra photon energy with respect to the molecular transitions. This matrix is built using a symmetric Liouville-space metric and obeys all known fundamental rules. Its direct calculation from refined potential-energy surfaces and promising modeling methods for forthcoming practical computations are outlined. A simple preliminary test for N2-N2 isotropic Raman line widths argues in favor of considerable effects of the internal perturber's structure on modeled spectral characteristics. [ABSTRACT FROM AUTHOR]