| Abstract
| - Previous work demonstrates that rates of H• losses generally increase much less rapidly with increasing internalenergy than do those of losses of polyatomic fragments. To determine whether this is also the case for thelosses of other atoms, the dependencies of the rates of Cl• and CH3• losses from CH3CHClCH3+• on ioninternal energy are compared. These dependencies were established experimentally by photoionization massspectrometry. The reactant ion and the transition states were characterized by B3LYP/6-31G(d), B3LYP/6-311G(d,p), and MP2/6-31G(d) theories. The transition states located are at very long bond lengths and closein energy to the corresponding dissociation products. Rate constants as a function of internal energy wereobtained by RRKM theory. According to both experiment and theory, above its onset, methyl loss increasesmuch more rapidly with internal energy than does loss of Cl•. This stems from three vibrational frequenciesbeing substantially lowered in the transition state for the former but not in the latter reaction as they are beingtransformed into rotations of the separated products. This produces a much more rapid increase in the RRKMsum of states for the transition state to CH3CHCl+ + CH3•, and thus also in the rate of that reaction. This,together with previous work, establishes that losses of polyatomic fragments from ions in the gas phasegenerally increase much faster with increasing internal energy than do losses of atoms.
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