| Abstract
| - Correlated, counterpoise corrected wave function calculations on the hydrogen−coronene system are used toinvestigate the energy landscape and the dynamic behavior of hydrogen atoms physisorbed on graphite. Theadopted MP2 correlation level, employing the aug-cc-pVDZ basis set augmented with bond functions, hasbeen selected after extensive investigation on the smaller hydrogen−benzene system. The computedphysisorption energy (39.7 meV) is in excellent agreement with the existing experimental value of (39.2 ±0.5) meV for a graphite single layer (Ghio, E.; Mattera, L.; Salvo, C.; Tommasini, F.; Valbusa, U. J. Chem.Phys.1980, 73, 557) and makes one confident of the computed barriers to diffusion. A simple, analyticalexpression of the corrugated potential energy surface fitted to the calculated energy values is then used in 3Dquantum dynamical calculations of the tunneling contribution to the diffusion coefficient. Results show thathydrogen atoms physisorbed on graphite are highly mobile on the surface even at T = 0 K. This suggests thathydrogen formation in cold, interstellar clouds can indeed occur down to very low temperatures throughrecombination of hydrogen atoms previously physisorbed on the surface of dust grains.
|
