Journal of Chemical Physics, Vol.112, No.1, 203-211, 2000
Effects of reagent rotation and the accuracy of the centrifugal sudden approximation in the H-2+CN reaction
This paper presents fully converged integral cross sections for the ground rovibrational state and some rotationally excited initial states for the title reaction on the TSH3 PES. The initial state selected time-dependent wave packet method has been employed in the calculation with all important K blocks in the body-fixed (BF) frame included. We find that CN rotational excitation up to j(2)=7 essentially has no effect on the integral cross section, while H-2 rotational excitation substantially reduces the cross section. As a result, the thermal rate constant can be obtained accurately by only taking into account the effect of H-2 rotational excitation. It is found that the resulting thermal rate constant is considerably smaller than the initial state selected rate constant for the ground rovibrational state. It is also smaller than the experimental rate constant by a factor of 3 and 30% at T=209 K and 447 K, respectively, indicating the TSH3 PES used in the calculation is not quantitatively accurate in describing the reaction. In addition, we examine in detail the accuracy of the centrifugal sudden (CS) approximation to the reaction. Comparison between this reaction and the H-2+OH reaction is also carried out when possible.