DISSOCIATION DYNAMICS OF ENERGY SELECTED PROPANOL IONS FROM A SIGMA-TYPE ION STRUCTURE

The dissociation rates of energy selected propanol ions and partially deuterated propanol ions have been investigated by photoelectron photoion coincidence. Cold CH3CH2CH2OH and CD3CH2CH2OH samples were introduced into the photoionization region of a time-of-flight mass spectrometer through a skimmed molecular beam. The ions dissociated via the loss of H and H2O, the latter dominating near threshold. These rates ranged from 10(5) to 10(7) s-1 near the dissociation onset. Slow dissociation from the ion-dipole complex C3H6+...H2O is inconsistent with the simultaneous occurrence of metastable H loss and the lack of hydrogen scrambling prior to dissociation. However, the dissociation rates for H2O loss and H loss are described well by assuming statistical dissociation from the sigma-type electronic ground state of the molecular ion, which lies 0.5 eV below the reported ionization onset. This mechanism is consistent with the simultaneous occurrence of metastable H loss and lack of hydrogen scrambling at low energies. Hydrogen tunneling does not play a role in either loss channel.