ASSOCIATION AND ISOTOPIC EXCHANGE-REACTIONS OF CH(CD)[X(2)PI]+CO

The reaction rates for (CH)-C-12 and (CD)-C-12 With normal isotopic ab undance CO and (CO)-C-13 have been studied at 293 K for pressures betw een 12.5 and 500 Torr and at 100 Torr for temperatures between 293 and 650 K. The pressure and temperature dependence of the addition reacti on of CH with CO have been measured. The addition rate coefficient can be fit to the expression 7.2+/-0.3x10(-12) (T/293)(-2.4+/-0.2) cm(3) molecule(-1) s(-1) at 100 Torr total pressure (He buffer). A fit of th e pressure dependence to a Tree expression with F-c=0.6 yields a low-p ressure rate constant (k(0)) of 2.4+/-0.3x10(-30) cm(6) molecule(-2) s (-1). The rate for carbon atom exchange has been measured by compariso n of the C-13 labeled and unlabeled reaction rates. The isotopic excha nge reaction is 1.0+/-0.2x10(-12) cm(3) molecule(-1) s(-1) at 20 Torr. The deuterium isotope effect on the exchange rate is large, with an i nverse kinetic isotope effect (k(H)/k(D))=0.28+/-0.08 at 20 Torr. This inverse isotope effect reflects the competition between collisional s tabilization and isomerization, and is a convolution of isotope effect s for the isomerization, unimolecular dissociation, and stabilization rates. The experimental results are consistent with a mechanism for ex change that involves isomerization of an HCCO adduct via an oxiryl int ermediate, and indicate that insertion into the C-O bond is not import ant in this reaction. (C) 1997 American Institute of Physics.