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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 $660cm-1$. 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, cause 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/6-31$G\ast$ level. The spectrum, molecular structure, harmonic force field and vibrational coupling will be discussed.