A new formulation of the theory of strong overlapping effects in molecular line broadening is presented in terms of the intermolecular potential. This formulation takes into account the vibrational degrees of freedom and includes in an acceptable form the close collisions. A detailed analysis of such effects is carried out for the motional narrowing arising in the Q branch of HD at sufficiently high densities. A very good consistency is obtained between the experimental data and the present calculation at room and low temperatures. The nonadditivity effects in infrared absorption and anisotropic Raman overlapping lines treated in the general frame of this paper may also be easily calculated when required.
Self-broadened nitrogen isotropic Q(J) Raman linewidths have been inverted to obtain effective rotation–translation (R–T) state-to-state rate constants using the energy corrected sudden (ECS) formalism. These rate constants are discussed as a function of the rotational levels J and temperature T. Collisional Q(J) line shifts have been investigated by high-resolution inverse Raman spectroscopy (IRS) over a wide temperature range. Semiclassical calculations lead to a clear understanding of their J and T dependence. This exhaustive study of both diagonal and off-diagonal relaxation matrix elements has allowed us to calculate the collisionally narrowed Q branch at high pressure. New measurements of N2 Q branch at high pressure have been performed by IRS. The good agreement of ECS profiles with IRS data, for various pressures and temperatures, underlines the consistency of the present R–T ECS scaling analysis.
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