15min:

T. TROXLER, Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland .

The S₁-S₀ electronic transition of jet-cooled 2-methoxynaphthalene (2MXN) has been investigated by use of laser-induced fluorescence spectroscopy. The fluorescence excitation spectrum revealed two electronic origin transitions, separated by 660 cm^-1. They are caused by the presence of a cis and a trans conformation of the methoxy group with respect to the naphthalene frame. Dispersed fluorescence spectra of 25 major transitions in the excitation spectrum of the cis conformer were recorded, employing a liquid nitrogen cooled charge-coupled device (CCD) detector. Atypical, highly structured emission indicates that extensive vibrational mixing in the S₁ electronic state of cis -2MXN occurs, caused by large normal coordinate (Duschinsky) rotation. Experimentally determined frequencies are compared to the predicted normal mode values of an ab-initio calculation at the HF/6-31G^** level. The spectrum, molecular structure, harmonic force field and vibrational coupling will be discussed.