Dynamics of Cr(CO)6+ collisions with hydrogenated surfaces

Classical trajectory simulations are used to study the activation of Cr(CO)(6)(+) ions by 5-110 eV collisions with n-hexyl thiolate self-assembled monolayer (SAM) and the H-terminated diamond {111} surfaces. The transfer of the ion's initial translational energy E-i to the ion's internal degrees of freedom E-int, to the surface E-surf, and to final translational energy E-f depends on both E-i and the surface. At E-i=70 eV the percent energy transfers to E-int, E-surf, and E-f are 9, 81, and 10 for collision with the SAM and 17, 29, and 54 for collision with diamond. For collision with the SAM, the percent energy transfer to E-int is 8-10% and nearly independent of E-i, while it depends on E-i for collision with diamond. The percent transfer to E-int, for collision with the SAM, is in excellent agreement with experiment. For both surfaces, the percent energy transfer to E-surf and to E-f increase and decrease, respectively, as E-i is increased. For E-i of 30 and 70 eV the Cr(CO)(n)(+), n=4-6, ions shatter as Cr(CO)(6)(+) strikes the diamond surface. At 110 eV some of the n=1-3 ions also begin to shatter. Shattering is only observed for collision with the SAM at an E-i of 110 eV, for which the n=4-6 ions shatter. At lower E-i, the Cr(CO)(6)(+) ions rebound off the SAM and dissociate via intramolecular vibrational energy redistribution, with lifetimes approximately the same as those of Rice-Ramsperger-Kassel-Marcus theory. Energy partitioning to the Cr(CO)(n)(+)-->Cr(CO)(n-1)(+)+CO, n=1-6, dissociation products is nonstatistical, with the partitioning to relative translation and CO vibrational and rotational energy, larger and smaller, respectively, than the prediction of phase space theory. There is negligible energy transfer to the CO vibration during the collision of Cr(CO)(6)(+) with either surface or later as a result of intramolecular vibrational energy redistribution after the Cr(CO)(n)(+) ions scatter off the surfaces. (C) 2003 American Institute of Physics.