PARTICIPATION OF METHYL INTERNAL-ROTATION IN THE VIBRATIONAL PREDISSOCIATION OF THE AROMATIC VAN-DER-WAALS COMPLEX P-FLUOROTOLUENE-AR

S-1-S-0 fluorescence excitation and dispersed fluorescence spectra fro m p-fluorotoluene-Ar (pFT-Ar) formed in a supersonic expansion are use d to characterize the vibrational predissociation (VP) from S-1 comple x levels with 800, 1200 and 2000 cm(-1) of vibrational energy. VP from the lower level occurs in al least 12 vibrational channels that invol ve only the three lowest energy pFT ring modes. VP from the higher lev els is different, but those two levels are a matched pair with respect to their VP characteristics. They have almost identical channels and branching ratios, including a dominant channel producing free pFT in i ts zero point level. That channel requires conversion of as much as 18 00 cm(-1) of ring mode vibrational energy into translational and rotat ional energy. These behaviors appear to be unique among the aromatic v an der Waals complexes so far studied, particularly with respect to th e non-selective nature of the VP channels. Evidence pointing to the ac tive participation of the methyl internal relation in the VP dynamics is presented. Conjecture is offered about how this internal rotation c ontributes to the highly unusual VP characteristics.