The model of exact trajectories involved in a semiclassical computation of (vib)rotational linewidths and shifts is extended to the case of asymmetric top colliders. General expressions for the second-order contributions to the scattering matrix are given which define the pressure broadening and shift of the line. This theoretical approach is tested on the particular case of the infrared ${\nu }_7$ band linewidths of ${\text{C}}_2{\text{H}}_4$ broadened by ${\text{N}}_2$ which is frequently required for atmospheric applications. The computed linewidths compare favorably with available experimental data.

• Received 6 December 2007

DOI:https://doi.org/10.1103/PhysRevA.77.042720