The [formula omitted] single vibronic level fluorescence and Raman spectra of styrene-β-D 2 vapor and their use in determining the C(1)-C(α) torsional potential function in the [formula omitted] state

Abstract

SVL fluorescence spectra of styrene-β-D 2 (STYD 2) are assigned and enable many new assignments to be made in the absorption spectrum. In turn these allow the determination of the first four levels of the C(1)-C(α) torsional vibration ν″ 42 in the ground electronic state. Using new information regarding the geometry of the molecule, in particular that 〉C(1)C(α)C(β) is about 130°, together with torsional vibrational levels from the electronic absorption spectrum and the Raman spectrum, has enabled us to determine the ν 42″ torsional potential function V( φ) for styrene (STY) and STYD 2: STY V(φ)/ cm −1 = [1070(1 − cos2φ) − 275(1 − cos4φ) + 7(1 − cos6φ)] 2 ; STYD 2 V(φ)/ cm −1 = [1070(1 − cos2φ) − 270(1 − cos4φ) + 4.5(1 − cos6φ)] 2 . This potential function changes appreciably when one quantum of ν″ 29, a substituent in-plane bending vibration, is excited. There is a very strong Duschinsky effect affecting ν 42 and ν 41, a substituent out-of-plane bending vibration, and intensity measurements in the SVL spectra have enabled us to obtain Duschinsky coefficients corresponding to the changes of normal coordinates from the X ̃ to the A ̃ state.