The stable conformations and vibronic and cation spectroscopy of 2-ethoxybenzonitrile

Abstract

Ethoxy-substituted benzene has several stable conformations as the single bond in the ethoxy group is capable of internal rotation. Ethoxybenzonitrile may has more conformers due to different orientations of ethoxy with respect to the CN group. In this paper, the potential energy surface (PES) of 2-ethoxybenzonitrile in the ground state was calculated at the level of B3LYP/cc-pvdz, and five different molecular conformers were found on the PES. Only the most stable conformer I (trans) was observed in the supersonic molecular beam experiments. The resonance enhanced multiphoton ionization (REMPI) and mass analyzed threshold ionization (MATI) spectra of 2-ethoxybenzonitrile were measured and Franck-Condon simulations were performed, and the theoretical results are in good agreement with the experimental measurements. The similar molecular structures in S0, S1, and D0 states imply the large Franck-Condon factors. The vibronic structures in S1 and D0 states were analyzed in detail and the vibronic features were assigned. The MATI spectra follow well the propensity rule Δν = 0, indicating that the molecular structures of the cationic and excited states are similar. Most of the observed vibrations are associated with the ring in-plane distortion. The band origin of the S1←S0 transition and the accurate adiabatic ionization energy of 2-ethoxybenzonitrile are determined for the first time to be 34 092 ± 2 and 69 796 ± 5 cm−1, respectively.