Electron-energy-loss spectroscopy of solid phenylacetylene

A high-resolution electron-energy-loss spectrum of solid phenylacetylene has been recorded. The lowest singlet–triplet transition (1 1A1→1 3A1) shows more vibronic bands than previously observed. Semi-empirical calculations suggest that this transition relates to the 3La band of benzene, but the irregular vibronic structure hints towards a noticeable contribution from the side group. The second singlet–triplet transition at 4.255 eV is also detected. According to the calculations it has two components (1 1A1→1 3B2,2 3A1) which correlate with the 3Ba,b band in benzene.