Quasi-bound complexes in collisions of different linear molecules: Classical trajectory study of their manifestations in rotational relaxation and spectral line broadening

Stable bimolecular complexes (tightly bound dimers) in the gas phase are usually created during third body stabilization of their unstable precursors-quasi-bound complexes (QCs). The latter can arise under the condition that at least one of the colliding partners has an internal degree of freedom. In this article, the principal difference between "orbitings" and QCs is demonstrated in the classical nonreactive scattering picture. Additionally, fractions of QCs in binary collisions of different linear molecules are compared. Also in the article the influence of QCs on rotational R-T relaxation and on vibration–rotational spectral line broadening is discussed. Explicit formulae shedding light on the QCs contribution to the R-T relaxation cross section and the line width and shift are presented. The obtained results emphasize the need for including QCs in every theoretical modeling of spectroscopic manifestation of intermolecular interactions. Besides the topics above, the possible manifestation of non-impact effects in the central regions of spectral lines due to QCs is stated. And finally, special consideration is given to the problem of adequate simulation of QCs formation at different pressures. - Highlights: • Principal difference between classical "orbitings" and quaibound complexes (QCs). • Fractions of QCs in binary collisions of different linear molecules as a function of rotational quantum number. • Influence of QCs on rotational R-T relaxation and vibration–rotational spectral line broadening; explicit formulae presented. • Importance of including QCs in any theoretical modeling of spectroscopic manifestation of intermolecular interactions. • Possible manifestation of non-impact effects in central regions of spectral lines due to QCs.