Ionic dissociation of methanol studied by photoelectron–photoion coincidence spectroscopy

Abstract

Ionic dissociation of methanol has been investigated by means of photoelectron–photoion coincidence spectroscopy. Breakdown curves and average kinetic energies released in the fragmentations were obtained as a function of molecular ion internal energy. In the CH2OH+ formation about 45% of the excess energy available for the dissociation is converted into translational energy of products. In contrast, the average translational energies released in the formation of CH3+ and HCO+ ions are 0.4 and 2.5 eV, respectively, and these values remain constant irrespective of the excess internal energy over the excited states of ions, 6a′−1, 1a″−1, and 5a′−1. All results including the breakdown curves reveal that the statistical theories of unimolecular decomposition can not give a satisfactory interpretation to mass spectra of methanol. Alternative mechanisms are discussed to account for the observations.