Communication: The origin of rotational enhancement effect for the reaction of H2O+ + H2 (D2)

We have measured the absolute integral cross sections (sigma's) for H3O+ formed by the reaction of rovibrationally selected H2O+((XB1)-B-2; v1(+)v2(+)v3(+) = 000; N(Ka)(+)Kc(+) = 0(00), 1(11), and 2(11)) ion with H-2 at the center-of-mass collision energy (Ecm) range of 0.03-10.00 eV. The sigma(0(00)), sigma(1(11)), and sigma(2(11)) values thus obtained reveal rotational enhancements at low E-cm < 0.50 eV, in agreement with the observation of the previous study of the H2O(+)((XB1)-B-2) + D-2 reaction. This Communication presents important progress concerning the high-level ab initio quantum calculation of the potential energy surface for the H2O+((XB1)-B-2) + H-2 (D-2) reactions, which has provided valuable insight into the origin of the rotational enhancement effect. Governed by the charge and dipole-inducedmultipole interactions, the calculation shows that H-2 (D-2) approaches the H end of H2O+((XB1)-B-2) in the long range, whereas chemical force in the short range favors the orientation of H-2 (D-2) toward the O side of H2O+. The reorientation of H2O+ reactant ion facilitated by rotational excitation thus promotes the H2O+ + H-2 (D-2) reaction along the minimum energy pathway, rendering the observed rotational enhancement effects. The occurrence of this effect at low E-cm indicates that the long range charge and dipole-induced-multipole interactions of the colliding pair play a significant role in the dynamics of the exothermic H2O+ + H-2 (D-2) reactions. (C) 2014 AIP Publishing LLC.