Akira Ichihara

Three-dimensional quantum reactive scattering calculations for the nonadiabatic (D+H2)+ reaction system

Three-dimensional quantum reactive scattering calculations have been carried out for the (D+H2)+ nonadiabatic ion–molecule collision. The calculations have been done using the time-independent close-coupling formalism with hyperspherical coordinates. The (3×3) diatomics-in-molecule potential energy surfaces have been employed. The result of the accurate quantum scattering calculations have been compared to the results of the quasiclassical trajectory surface hopping method. Two versions of the method have been used; one uses Tully’s fewest switches algorithm and the other is the trajectory surface hopping method of Tully and Preston, in which electronically nonadiabatic hopping is only allowed at the predefined crossing seams. We have found that the agreement between the quantum result and the result of Tully’s method is generally good, but the Tully and Preston method significantly underestimates the nonadiabatic transition probability.

Ab initio potential energy surfaces for the two lowest 1A′ states of H+3

Three‐dimensional potential energy surfaces of H+3 in the two lowest 1A′ electronic states have been calculated by the full configuration interaction method with a [8s6p2d1f] Gaussian‐type basis set. The features of the avoided crossing of two surfaces as well as the energy minimum of the 1A′ ground state have been produced by the potential calculation at 680 different spatial geometries. These surfaces should be useful for the detailed studies of charge transfer and chemical reaction in the H+ and H2 collisions.

Cross sections for the reaction H+ + H2 (v = 0-14) →H + H2+ at low collision energies

Cross sections for the reaction H+ + H2→H + H2+ have been calculated in the centre-of-mass collision energy range of Ecm≤20 eV by using the trajectory-surface-hopping method. The vibrational quantum number of the reactant H2 has been taken to be in the range 0≤v≤14, and the effect of v on H2+ production has been investigated. The results show that H2+ production increases rapidly as v increases up to v = 5, 6, and then decreases with further increase of v. The Maxwellian-averaged rate coefficients, which are expressed as functions of the plasma and H2 temperatures (T,E), have been estimated from the calculated cross sections in the range 0.1≤T, E≤5.0 eV.

A study on ion–molecule reactions in the H+3 system with the trajectory‐surface‐hopping model

Cross sections for ion production in the D++H2, D++D2, and H++D2 collisions have been calculated in the center‐of‐mass collision energy range of 2.5 to 8.0 eV by using trajectory‐surface‐hopping method on ab initio potential energy surfaces. For the production of H+ and HD+ ions in the D++H2 collisions the present results agree with experiments. For the production of D+2 ions in the D++D2 collisions the calculations show agreement with the experimental results at energies below 4.5 eV, but lead to an overestimate above 5.0 eV. For the production of D+ and HD+ ions in the H++D2 collisions, agreement between the calculations and experiments is good in the whole energy range, while a deviation comes out between both the results for the charge transfer H++D2→D+2+H above 5.0 eV. As far as the energy dependence of cross sections is concerned, the present calculations well reproduce all the experiments, owing to the use of the ab initio surfaces, instead of the diatomics‐in‐molecules surfaces.