Rotational state dependence of ion-polar molecule reactions at very low temperature

The adiabatic rotational state method is used to investigate the rotational state dependence of the rate coefficients for ion-polar molecule reactions in the very low temperature regime characteristic of interstellar molecular clouds. Results obtained for the systems H ₃ ⁺ +HCl and H ₃ ⁺ +HCN indicate that all the methods based on the adiabatic separation of the rotational and radial motion of the collision complex — adiabatic capture centrifugal sudden approximation (ACCSA), statistical adiabatic channel model, classical adiabatic invariance method — agree very satisfactorily in the low temperature limit. Discrepancies observed between some of the published data would appear to arise from numerical inaccuracies rather than from any defect of the theory.