Double ionization of 2-butyne, 2-pentyne, 2-hexyne and 3-hexyne to singlet and triplet electronic states of their dications

The double-ionization energies (DIEs) of 2-butyne, 2-pentyne, 2-hexyne and 3-hexyne molecules to singlet and triplet electronic states of their dications have been measured using double-charge transfer spectroscopy. Values of DIEs to the lowest singlet and triplet states of the four dications were calculated using an ab initio method and the split-valence 3-21G and 6-31G basis sets. The pattern of those DIEs for the four molecules (and the previously studied propyne molecule) agree with that observed in the experimental values, thus giving an insight into the double-ionization processes of part of the alkyne family of molecules. The spectra showed many other peaks which correspond to double ionization to electronically excited states, For 2-butyne, the DIE values to those states calculated using a semi-empirical form of the multiple-scattering X alpha computational method allowed the relevant electronic transition to be identified. (C) 1997 John Wiley & Sons, Ltd.