Book Description

The structure and energetics of free radicals, ions, and clusters have been investigated by photoelectron photoion coincidence (PEPICO) and analyzed with the aid of ab initio molecular orbital and statistical theory (RRKM) calculations. The two major themes are the quantitative analysis of unimolecular reactions with no adjustable parameters, and the study of cluster ion dissociation processes. Molecules (or free radicals) were prepared in a molecular beam so that they are translationally and vibrationally cold. The translational temperature was calculated from the measured time of flight (TOF) peak width, while the vibrational temperature was determined from the shift in the dissociation onset. Free radicals are produced by pyrolysis in the nozzle, and subsequent cooling of the free radicals is demonstrated. Ion dissociation rates in the range from 104 to 107 sec−1 are measured from the asymmetric TOF distribution. This method was used to measure the dissociation rates of a number of cold and warm ions, among them HCl (DCl) loss from C2H5Cl (C2D5Cl), a reaction that proceeds via tunneling. The analysis of the butene ion dissociation provided information about the role of angular momentum in dissociation reactions. This dissociative ionization of ethylene clusters demonstrated that ethylene dimer ions rearranged to butene ions prior to dissociation. Finally, a new value for the t-butyl ion heat of formation, which corrects a 15 kJ/mol error in the previous value, was obtained from the 0 K breakdown diagram of t-butyl iodide.