Rotational dependence in the linewidth of the ultraviolet transitions of OH

Abstract
The homogeneously broadened linewidth of OH due to collisions with water molecules was found to decrease with increasing rotational excitation, and tended to level off to a constant value. This observed dependence is a manifestation of the rotational distribution of the water molecule through rotational transitions in near resonance with those of the OH. The constant value at high rotational excitation reflects the nonresonant contributions to the homogeneous linewidth similar to those due to nonpolar molecules.