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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.

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This explanation is in essence similar to the isolated states proposed by McAdoo and McLafferty. The difference is that we assume them to be isomeric structures rather than electronic structures of the butanoic acid.Acknowledgment. Tomas Baer acknowledges his sincere gratitude to Simon Bauer for providing an exciting and stimulating atmosphere during his 4 years at Cornell. Si's enthusiasm for the new and the unexpected were then, and still are now, a constant source of inspiration. We are grateful to the National Science Foundation for the support of a portion of this work. The structure and energetic studies were supported by the Department of Energy.

more stable structure even though at least four such ionic structures (ethyl acetate and its enol, and butanoic acid and its enol) are more stable. In addition, dioxane(+) does not produce fragment ions and neutrals in their most stable configuration. Instead, products which can be formed by simple bond cleavages from dioxane tend to be formed.The RRKM/QET calculated dissociation rates agree extremely well with measured decay rates of internal energy selected metastable dioxane ions. From these data as well as kinetic energy release results for the C3H60+ + CH20 production we conclude that the ion formed has the CH2-0-CH2CH2 structure and has a AHf°298 = 828 ± 8 kJ/mol. This compares very well with an ab initio calculated energy of 833 ± 17 kJ/mol.25 The RRKM/QET calculations also suggest that the transition states, par-ticularly for the m/e 44 and 45 production, are very tight. That is, the transition state structure is a highly strained one.Acknowledgment. Tomas Baer acknowledges his sincere gratitude to Simon Bauer for providing an exciting and stimulating atmosphere during his 4 years at Cornell. Si's enthusiasm for the new and the unexpected were then, and still are now, a constant source of inspiration. We are grateful to the National Science Foundation for the support of a portion of this work. The structure and energetic studies were supported by the Department of Energy.