Effect of collision-induced phase shifts on the linewidths and line shifts of rotational spectral lines

A more general theory of the width and shift of microwave absorption lines is developed under the impact approximation with the effect of elastic as well as inelastic collisions being considered in a more rigorous way. Previous formulations (Anderson and Murphy–Boggs) are shown to be limiting cases of this treatment. The theory is applied to pure rotational transitions of the OCS–OCS, OCS–He, and OCS–Ar systems and the results compared with experiment. The agreement is very satisfactory for the quantum number dependence and temperature dependence of the linewidths and for the approximate magnitude of the pressure-induced line shift.