Insertion vs abstraction in the reactions of NH(a(1)Delta,nu=0, 1) with H-2 and D-2

Gas-phase reactions of NH(a(1) Delta, nu = 0, 1) + H-2 (1) and NH(a(1) Delta, nu = 0, 1) + D-2 (2) were studied in the photolysis of HNCO/H-2 (or D-2) mixtures. NH(a(1) Delta) and product H (D) atom were detected by UV and vacuum-UV laser-induced fluorescence. The observed rate constants at room temperature (295 +/- 2 K) and activation energies in the range of 295-407 K were; NH(a, nu = 0) + H-2 --> product(1-0), k(1-0) = 3.76 +/- 0.59, E(a) = 5.7 +/- 0.7 NH(a, nu = 1) + H-2 --> product(1-1), k(1-1) = 3.09 +/- 0.26, E(a) = 6.5 +/- 1.2 NH(a, nu = 0) + D-2 --> product(2-0), k(2-0) = 2.72 +/- 0.25, E(a) = 6.5 +/- 1.1 NH(a, nu = 1) + D-2 --> product(2-1), k(2-1) = 2.88 +/- 0.35, E(a) = 6.6 +/- 1.1 in units of 10(-12) cm(3) molecule(-1) s(-1) and kJ mol(-1). The product branching ratio in reaction 2 was determined to be [D]/[H]=3.2 +/- 0.76, in which no temperature dependence was indicated. These results are consistent with insertion mechanism having a loose entrance transition state structure, which is suggested by ab initio CI calculations. In contrast, the contribution of direct abstraction channel is supposed to be negligibly small.