Abstract
The isomerization of methyl isocyanide (CH/sub 3/NC) to acetonitrile (CH/sub 3/CN) was studied by excitation of the 5nu/sub C-H/ (726.6 nm) and 6nu/sub C-H/ (621.4 nm) overtone states, which lie about 1 and 8 kcal/mol, respectively, above the isomerization barrier. Products yields were measured as a function of pressure and collision partner. A Stern-Volmer plot (yield/sup -1/ vs. pressure) shows that (1) deactivation by collision with pure CH/sub 3/NC is more rapid than with C/sub 3/H/sub 6/, SF/sub 6/, or Ar, (2) the collisional deactivation efficiencies decrease in going from C/sub 3/H/sub 6/ to SF/sub 6/ to Ar, and (3) the single-collision deactivation approximation (strong collider approximation) fails for both the 6nu/sub C-H/ and 5nu/sub C-H/ data. With the use of a master equation solution, assuming an exponential down energy-transfer function, the average energy transferred in a deactivating collision, - /sub down/, is extracted from each data set, as well as the average energy transferred fer collision, - . It is concluded that the isomerization yield depends markedly on the collision partner and on the average energy transferred per collision, - , even though the single-collision deactivation approximation might have been expected to have its greatest validity in this energy regime.
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