Laser probes of intramolecular energy transfer between internal rotation and vibrations in large polyatomics

Laser excited S₁→S₀ fluorescence spectra are obtained from p-fluorotoluene in a supersonic jet in order to probe internal rotational-vibrational coupling. Resolved fluorescence spectra after selective excitation of S₁ levels with high quanta states of the CH₃ internal rotation contain evidence of extensive interactions with isoenergetic vibrational levels. Analogous spectra from states without excitation of the internal rotor show little or no interactions. The results are consistent with a recently developed theory of the intramolecular collisional transfer of rotor energy to the vibrational field.