Rotational excitations in para-H2+para-H2 collisions: Full- and reduced-dimensional quantum wave packet studies comparing different potential energy surfaces

Abstract

We study the process of rotational excitation in the collisions of para-H(2) with para-H(2) by propagating wave packets with the multiconfiguration time-dependent Hartree (MCTDH) algorithm. Transition probabilities are then calculated by the method of Tannor and Weeks based on time-correlation functions. Calculations were carried out up to a total angular momentum of J=70 to compute integral cross sections up to 1.2 eV in collision energy and thermal rate coefficients from 100 to 3000 K. The process is studied on the full-dimensional potential energy surface of Boothroyd-Martin-Keogh-Peterson (BMKP) as well as on the rigid rotor surface of Diep and Johnson. We test the validity of the rigid rotor approximation by also considering two rigid rotor restrictions of the BMKP potential energy surface (PES). Additionally, we investigate a variant of the BMKP PES suggested by Pogrebnya and Clary [Chem. Phys. Lett. 363, 523 (2002)] with reduced anisotropy. We compare our results with previous theoretical data for the cross sections and with experimental data for the rate coefficients at low temperatures.

Vibration-vibration and vibration-translation energy transfer in H2-H2 collisions: A critical test of experiment with full-dimensional quantum dynamics

“…13,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] Quantum calculations are the primary source of state-resolved rate coefficients for astrophysical modeling. Excitation of rotational and vibrational levels of H 2 by collisions with H, H + , He, H 2 , and electrons followed by emission of quadrupole radiation is considered to be the main cooling mechanism of the primordial gas.…”

“…As a result, many of the early H 2 -H 2 calculations resorted to the rigid-rotor approximation. However, in the last several years, a number of full-dimensional quantum calculations have been reported within the timedependent 45,47,[49][50][51][52] and time-independent 13, 44, 46, 53-55 quantum formalisms. Some of these calculations have adopted the coupled-states approximation, [44][45][46][47] which was shown to be reliable.…”

Fully converged integral cross sections of collision induced dissociation, four-center, and single exchange reactions, and accuracy of the centrifugal sudden approximation in H2 + D2 reaction

“…Another area of interest in the study of the H 4 system are the calculation of nonreactive vibrational de-excitation cross sections using full-dimensional QM methods of both time-independent [46][47][48][49] and time-dependent type. 50,51 Recently, we performed full-dimensional time-dependent wave packet calculations of the H 2 + D 2 reaction and its isotopic variants on the ASP and BMKP PESs with J = 0. 52 The role of both vibrationally and rotationally excited reagents was examined.…”

A comparative study of the low energy HD+o-/p-H2 rotational excitation/de-excitation collisions and elastic scattering

“…These PESs have been used in several different calculations. [32][33][34][35][36] However, in our previous works 12,34 we found that in the case of low energy H 2 +H 2 collision these PESs provide different results for some specific state-resolved cross sections. The difference may be up to an order of magnitude.…”