The photoelectron spectra of allene, deuteroallenes and tetrafluoroallene

The photoelectron spectra of allene, allene 1.1-d 2 , allene-d 4 and tetra­fluoroallene have been measured in the region 6–20 eV. Allene shows three vertical ionization potentials at 10.02, 14.75 and 17.3 eV. The first band, involving ionization from a π orbital, shows a complex vibrational struc­ture, but there is a marked convergence of the intervals towards the higher energy side. It is suggested that the main coupled vibration is the torsional mode. The band appears to involve a Jahn–Teller effect, but there are two sub-maxima, and current theory seems insufficient to account for all the observed features. The spectra of the deuteroallenes show similar bands, the vibrational intervals being affected by the isotope effect. The photoelectron spectrum of tetrafluoroallene shows three bands at 11.24, 16.26 and 17.00 eV. The first band, associated with ionization from a π orbital, shows a coupled vibrational frequency of 1450 cm -1 . The infrared and Raman spectra of tetrafluoroallene have been measured in order to determine the molecular vibration frequencies and all eleven frequencies have been assigned. The first band in the photoelectron spec­trum has been interpreted as involving the C═C═C symmetrical stretching vibration in the ion, and there is no sign of a Jahn–Teller effect.