Die Photoelektron‐Spektren der Monohalogenacetylene

Abstract

The photoelectron spectra of the four monohaloacetylenes XCCH with X  F, Cl, Br, I have been recorded. The first four bands of these spectra are assigned (in order of increasing ionization potentials) to the following states: band 1: ²Π_3/2(1), ²Π_1/2(1); band 2: ²Π_3/2(2), ²Π_1/2(2); band 3: ²Σ⁺(3); band 4: ²Σ⁺(4). A correlation diagram based on a simple ZDO‐MO model shows that the observed band positions and the size of the splits due to spin‐orbit coupling can be satisfactorily explained in terms of such a model. It is found that the orbital energies A_X of the postulated halogen npλ(X)‐basis orbitals are a linear function of the ionization potentials I(X) of the free atoms X. The validity of the ZDO‐MO‐model is confirmed by the excellent qualitative agreement between the observed and predicted spacings of the vibrational fine structure of the π‐bands.