Full-dimensional quantum dynamics calculations of H$_2-$H$_2$ collisions

We report quantum dynamics calculations of rotational and vibrational energy transfer in collisions between two para-H$_2$ molecules over collision energies spanning from the ultracold limit to thermal energies. Results obtained using a recent full-dimensional H$_4$ potential energy surface (PES) developed by Hinde [J. Chem. Phys. {\bf 128}, 154308 (2008)] are compared with those derived from the BMKP PES [J. Chem. Phys. {\bf 116}, 666 (2002)]. For vibrational relaxation of H$_2(v=1,j=0)$ by collisions with H$_2(v=0,j=0)$ as well as rotational excitations in collisions between ground state H$_2$ molecules, the PES of Hinde is found to yield results in better agreement with available experimental data. However, for highly efficient near-resonant rovibrational transitions that conserve the internal rotational angular momentum, both PESs yield similar results. In the absence of the near-resonance mechanism vibrational relaxation is driven by the anisotropy of the potential energy surface.