Born-Oppenheimer quantum dynamics of the C(1D)+H2 reaction on the CH2 (a)over-tilde 1A1 and (b)over-tilde 1B1 surfaces

We present the Born-Oppenheimer coupled-channel dynamics of the reaction C-12(D-1) + H-1(2)(X (1)Sigma(+)(g)) -> CH(X (II)-I-2) + H(S-2), considering the uncoupled CH2 states (a) over tilde (1)A(1) and (b) over tilde B-1(1), the permutation-inversion symmetry, and Coriolis interactions. Using accurate MRCI potential energy surfaces (PESs), we obtain initial-state-resolved reaction probabilities, cross sections, and rate constants through the time-dependent, real wavepacket (WP) and flux methods, taking into account the proton-spin statistics for both electronic species. Comparing results on both PESs, we point out the role of the (b) over tilde B-1(1) upper state on the initial-state-resolved dynamics and on the thermal kinetic rate. WP probabilities at J=0 and cross sections at E-col=0.080 eV agree quite well with quantum-mechanical time-independent findings. Probabilities and WP snapshots show the different reaction mechanisms on the PESs, i.e., an (a) over tilde (1)A(1) indirect perpendicular insertion and a (b) over tilde B-1(1) direct sideways collision, associated with many and few sharp resonances, respectively. All cross sections are very large at low E-col, decrease at high energies, and that of the lowest reactant state presents some weak resonances. As the temperature increases from 100 to 400 K, the (a) over tilde (1)A(1) rate constant increases slightly from 1.37 x 10(-10) to 1.43 x 10(-10) cm(3) s(-1), whereas the (b) over tilde B-1(1) one decreases from 1.30 x 10(-10) to 0.98 x 10(-10) cm(3) s(-1). In this temperature range, the (b) over tilde B-1(1) contribution to the total rate constant thus decreases from 49% to 41%. At 300 K, the WP and experimental rates are equal to (2.45 +/- 0.08) x 10(-10) and (2.0 +/- 0.6) x 10(-10) cm(3) s(-1), respectively. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3226573]