Pressure broadening and temperature dependence of microwave and far infrared rotational lines in OH perturbed by N2, O2, and Ar

Absorption linewidths associated with microwave transitions across A-doublets and pure rotational transitions of the free hydroxyl radical OH perturbed by N-2, O-2, and Ar are computed for temperatures ranging from 194 to 300 K within the framework of the Robert-Bonamy semiclassical formalism using exact trajectories. The calculation is done for the Hund's coupling case (a) which is expected to be a good approximation for the low rotational quantum numbers so far experimentally studied. As intermolecular potential, the usual sum of electrostatic and atom-atom interactions is taken. Unlike previous theoretical predictions, our computed values are found to be in good agreement with measurements. (C) 2001 Elsevier Science.