One-color resonance enhanced two-photon ionization spectroscopy of phenylacetonitrile and its Franck-Condon simulation

Abstract

Phenylacetonitrile (PAN) is widely used in the synthesis of medicines, pesticides, dyes, optoelectronic materials and quinoline derivatives, and has attracted much attention in related fields. In this paper, we report the one-color resonance enhanced two-photon ionization spectra of PAN obtained with ultrasonic molecular beam technique for the first time. The band origin of the S₁ ← S₀ electronic transition is determined to be (37646 ± 2) cm^–1. Density functional theory B3LYP/6-311G++(d, p) and B3LYP/aug-cc-pvtz are used to calculate the structures, energy and vibrational frequencies of the molecule. Based on these calculations Franck-Condon spectral simulations are performed. The measured vibrational frequencies are analyzed in detail. Combined with theoretical calculation, the spectral assignments are given as accurately as possible. Theoretical and experimental results are in good agreement with each other, and show that the spectrum in the low frequency region has a great signal-noise ratio and resolution, while in the high frequency region the spectrum shows opposite characteristics, revealing that the high background in high frequency region originates from dense and weak overtone and combined vibrations. Many spectral bands are found, and most of them may be assigned to the in-plane ring deformation, and theoretical calculations suggest that this is related to the expansion of the aromatic ring during the transition.