Detailed analysis of the vibronic structure of phenetole in its first excited state and ionic ground state.

The vibronic structure of the first electronically excited state S1 and ionic ground state D0 of phenetole has been investigated by means of resonance enhanced multi photon ionization (REMPI) and mass analyzed threshold ionization (MATI) spectroscopy. The vibronic levels were assigned with the aid of quantum chemical calculations at the (TD)DFT level of theory and a multidimensional Franck-Condon approach. The S1 excitation energy of phenetole has been determined to be 36370 ± 4 cm-1 (4.5093 ± 0.0005 eV). The adiabatic ionization energy was determined to be 65665 ± 7 cm-1 (8.1415 ± 0.0008 eV). The vibronic structure has been analyzed whereby the in-plane bending vibration νbend shows high activity in the first excited state but is more pronounced in the ionic ground state. Moreover, a strong Duschinsky rotation effect can be observed for several D0←S1 transitions that causes violations of the Δv = 0 propensity rule.