Anion photoelectron spectroscopy and high level ab initio calculations of the halide–acetylene dimer complexes

Abstract Anion photoelectron spectra are presented for the halide–acetylene complexes, X − ⋯C 2 H 2 where X = Cl, Br, and I. Electron binding energies are determined to be 4.1, 3.8 and 3.4 eV, respectively. Results from CCSD(T) calculations are presented for the neutral halogen–acetylene complexes. Two minima are predicted corresponding to a linear C ∞ v and T-shaped C 2 v geometry, with the T-shaped geometry stationary point predicted to be the global minimum. The form of the photoelectron spectrum is determined via prediction of the Franck–Condon factors linking the anion and neutral states.