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

Abstract

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 Ei to the ion’s internal degrees of freedom Eint, to the surface Esurf, and to final translational energy Ef depends on both Ei and the surface. At Ei=70 eV the percent energy transfers to Eint, Esurf, and Ef 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 Eint is 8–10% and nearly independent of Ei, while it depends on Ei for collision with diamond. The percent transfer to Eint, for collision with the SAM, is in excellent agreement with experiment. For both surfaces, the percent energy transfer to Esurf and to Ef increase and decrease, respectively, as Ei is increased. For Ei 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 Ei of 110 eV, for which the n=4–6 ions shatter. At lower Ei, 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.