Molecular spectra and structure of selenophen

Abstract

The infrared, Raman, and near ultraviolet spectra of selenophen have been measured. The vibrational spectra are consistent with the hypothesis of a planar structure for selenophen, a conclusion in contrast to that of previous investigations by Milazzo and co-workers. The 21 fundamentals are assigned to the irreducible representations of symmetry group C_2v, on the basis of Raman intensities and polarisations, band contours in the infrared vapour spectrum, and activation in the liquid and solid infrared spectrum of A₂-frequencies. The assignments to the approximate normal modes were made by analogy with those of thiophen. The near ultraviolet spectrum shows composite continuous absorption in the range 37,000–47,500 cm.^–1. No traces of narrow peaks previously reported by Milazzo et al. in this spectral region were observed. The diffuse vibronic bands superposed to a continuum in the region 47,500–51,300 cm.^–1 are interpreted on the basis of 405, 635, 1150, and perhaps 1350 cm.^–1 excited-state totally symmetric vibrational frequencies with their origin at 47,800 cm.^–1 This assignment is in disagreement with that proposed by Milazzo and co-workers.