Infrared Laser Induced Fluorescence Studies of State Mixing in Ground Electronic State Molecules
Journal Article
Overview
abstract
AbstractDuring the past several years, infrared laser induced fluorescence experiments in our laboratory have been used to probe the nature of state mixing in the C—H stretch fundamental frequency region of various organic molecules. Both total and dispersed IR fluorescence have been collected from molecules, cooled and isolated in a molecular beam, after excitation with an infrared optical parametric oscillator. Measurements of the dilution factor, which is inversely related to the number of coupled states, as a function of molecule, vibrational band, and average J value excited have yielded the result that the extent of state mixing is J dependent and scales linearly with J. The extensive body of data on the dilution factors has also provided an empirical correlation between the dilution factors and the density of rovibrational states. This relationship shows that about 70 rovibrational states/cm−1 of proper J and symmetry are necessary to ensure substantial state mixing, regardless of molecular structure. The relative energy contents of various vibrational modes after laser excitation can also be determined. A statistical mixing model has been refined to the point of being able to predict dilution factors and their J dependence as well as the relative energy contents of the modes which are involved in the makeup of the mixed excited states. This model assumes equal coupling between all the zeroth order rovibrational states that have the correct energy, symmetry, and J to couple to a given optically active state. The only adjustable parameter in this model is the average energy width over which the character of the zeroth order optically active excited state is spread, which is determined to be ˜0.05 cm−1.
