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 th eir dications have been measured using double-charge transfer spectros copy. Values of DIEs to the lowest singlet and triplet states of the f our 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 wit h that observed in the experimental values, thus giving an insight int o the double-ionization processes of part of the alkyne family of mole cules. The spectra showed many other peaks which correspond to double ionization to electronically excited states, For 2-butyne, the DIE val ues to those states calculated using a semi-empirical form of the mult iple-scattering X alpha computational method allowed the relevant elec tronic transition to be identified. (C) 1997 John Wiley & Sons, Ltd.