The dissociation dynamics of energy selected ion-dipole complexes. I. The cyclopropane ion-water complex [c-C3H6+-OH 2]

Abstract

The dissociation dynamics of energy selected n-propanol ions have been investigated by photoelectron photoion coincidence (PEPICO) and laser photodissociation. In spite of the low activation energy, the dissociation rates for the loss of H2O were found to be slow (<106 s -1) near the dissociation limit, but they increase rapidly with ion internal energy. The photodissociation experiment indicates that the n-propanol ion structure is maintained up to the dissociation limit. However, the reaction rate and the kinetic energy release show that H2O loss proceeds via an isomerized C3H8O+ structure. Ab initio calculations suggest that the isomerized structure is the ion-dipole complex formed by the cyclopropane ion and water. The dissociation rate is calculated with the statistical theory (RRKM/QET) by using vibrational frequencies determined from the ab initio calculation. Although the ion-dipole complex potential well is deeper than that of propanol, it does not account for the slow dissociation rate. The discrepancy of more than four orders of magnitude is attributed to the extremely anharmonic interaction potential associated with the ion-dipole forces. © 1987 American Institute of Physics.