Angular-distribution He(I) /Ne(I) /Ar(I) photoelectron spectra of unsaturated hydrocarbons

The energy dependence of the anisotropy parameters of the π- and selected σ-bands of ethylene, 1,3-butadiene, benzene, cyclohexene, norbornadiene, 1,3-and 1,4-cyclohexadiene has been determined in the low energy region. Whereas the behaviour of the σ-bands is much less uniform, all π-band β-values decrease with decreasing energy towards similar threshold values. Strong intra-band energy dependencies have been observed for both π and σ orbitals, while in the multiple π-orbital molecules there is a symmetry-specific contribution to the π β-values. Marked intensity variations are observed among the ethylene, butadiene and benzene bands, and the anisotropy-parameter-based assignment of symmetric character to the 1,4-cyclohexadiene first band is confirmed.