Spectroscopic characterization of structural isomers of naphthalene: 1-Phenyl-1-butyn-3-ene

Abstract

Laser induced fluorescence (LIF), single vibronic level dispersed fluorescence (DFL) spectra, and high resolution rotationally resolved scans of the S 0–S 1 transition of the C 10H 8 isomer 1-phenyl-1-butyn-3-ene have been recorded under jet-cooled conditions. The S 0–S 1 origin of PAV at 34 922 cm −1 is very weak. A vibronic band located 464.0 above the origin, assigned as 30 1 0, dominates the LIF excitation spectrum, with intensity arising from vibronic coupling with the S 2 state. High resolution scans of the S 0–S 1 origin and 30 1 0 vibronic bands determine that the former is a 65:35 a: b hybrid band, while 30 1 0 is a pure a-type band, confirming the role for vibronic coupling and identifying the coupled state as the S 2 state. DFL spectra of all vibronic bands in the first 800 cm −1 of the spectrum were recorded. A near-complete assignment of the vibronic structure in both S 0 and S 1 states is obtained. Herzberg–Teller vibronic coupling is carried by two vibrations, ν 28 and ν 30, involving in-plane deformations of the vinylacetylene side chain, leading to Duschinsky mixing evident in the intensities of transitions in excitation and DFL spectra. Extensive Duschinsky mixing is also present among the lowest five out-of-plane vibrational modes, involving motion of the side chain. Comparison with the results of DFT B3LYP and TDDFT calculations with a 6-311+G(d,p) basis set confirm and strengthen the assignments.