Energy transfer in molecular hydrogen plays an important role in the cooling of shock fronts in star-forming regions of the interstellar medium. Because shocked gas is far from equilibrium, state-specific information is required. To date, full dimensional quantum calculations are feasible only for collisions involving only low \((v,j)\) states lying below 1 eV of internal energy. Yet cross sections are needed for energy transfer involving states with higher internal energy. These are not currently accessible through quantum calculations and must be obtained by other methods such as quasiclassical trajectories.

Quasiresonant energy transfer occurs when internal energy is preserved in a collision with redistribution among internal degrees of freedom. In this study, quasiclassical trajectories were carried out on two potential energy surfaces for the H\(_2\) + H\(_2\) system to examine how well collisional outcomes conform to the energy gap law. Transitions of the type H\(_2 (v,0)\) + H\(_2(v',0) \rightarrow\) H\(_2 (v+1,0)\) + H\(_2(v'-1,0)\) or H\(_2 (v-1,0)\) + H\(_2(v'+1,0)\) are examined as a function of collisional energy Deviations from the exponential gap law are expected due to the anharmonicity of H\(_2\) and the accessibility of the rotational degrees of freedom. This is explored as a function of collisional energy and initial vibrational states. Insights gained may be used to estimate cross sections for transitions of interest.

The two six-dimensional potential energy surfaces used are the Hinde and the BMKP2 surface. The former is believed to be more accurate with respect to weak interactions., while the latter is a global surface which does not break down for large vibrational excitation. Results from calculations on both potentials will be compared.