Abstract
We study the process of rotational excitation in the collisions of para-H2 with para-H2 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