Theoretical studies of CN + H 2 ( D 2 ) reactions: competition between H(D)-abstractions in H ( D ) + HCN ( DCN ) / HNC ( DNC ) channels

The CN+H2 reaction was investigated by considering the two possible channels, H+HCN and H+HNC, taking into account the isotopic effects and with the vibrationally excited states. The frequencies and structures for all species of the CN+H2/D2 reaction were calculated using G3 method for further kinetics calculation. The thermal rate constants were calculated using the conventional transition-state theory (TST) and canonical variational transition-state theory (CVT) by APUAMA code, over the temperature range from 200 to 4000 K. In addition, rate coefficients for vibrationally excited reactants CN (v = 1) or H2 (v = 1) or D2 (v = 1) are presented.The branching ratio for the partitioning into H/D + HCN/DCN or H/D + HNC/DNC has, also, been determined. The results showed that the CN(v=0)+H2(v=0)→H+HCN channel is dominant at all range of temperature, while CN(v=1)+H2(v=0)→H+HNC channel is dominant at T ≥ 1900 K.The isotopic effects are the same behavior that CN(v=0,1)+H2(v=0,1)→H+HCN/HNC reactions. Reasonable agreement was found between the experimental results and the rate constants predicted by conventional transition-state theory, with tunneling correction, using the theoretical transition-state properties.