HIGH-RESOLUTION ELECTRONIC SPECTROSCOPY OF MOLECULAR CONFORMERS - METHYL-3-METHOXYBENZOIC ACID ESTER

By combining the techniques of rotationally resolved fluorescence exci tation spectroscopy in molecular beams and ab initio quantum mechanics , we have determined the identity of the four conformers that contribu te to the S-1<--S-0 electronic spectrum of methyl-3-methoxybenzoic aci d ester in the gas phase. Each conformer exhibits a unique spectrum. E ach conformer also exhibits a differently oriented electronic transiti on moment (TM) in the molecular Game, for which the distinguishable in ertial and electronic contributions also have been determined. The res ults suggest that the S-1<--S-0 TM vectors of all conformers are rotat ed by relatively large (counterclockwise) angles with respect to the a inertial axes, placing them close to the b axis of a -OCH3 substitute d benzene, and that the exact values of these angles depend upon the m utual conformations of both attached groups with respect to each other .