Effect of surface stiffness on the efficiency of surface-induced dissociation

Classical trajectory simulations are performed to study the energy transfer and unimolecular dynamics associated with collisions of Cr(CO)₆⁺ions with n-hexyl thiolate self-assembled monolayer (SAM) and diamond {111} surfaces at a collision energy and angle of 30 eV and 45°. The trajectories are calculated with an analytic potential energy function fit to high-level ab initio calculations and experimental data. The "soft" SAM and "hard" diamond surfaces have highly different collision dynamics. The average percent energy transfer to Cr(CO)₆⁺ internal degrees of freedom, the surface, and Cr(CO)₆⁺ translation are 10, 60 and 21% respectively, for the SAM surface and 30, 14 and 56% for the diamond surface. The Cr(CO)₆⁺ ions, which collide with the SAM surface, dissociate by intramolecular vibrational energy redistribution (IVR) and lifetimes in accord with RRKM theory. In contrast, Cr(CO)₆⁺ ions, activated by collision with the diamond surface, dissociate via direct translation to vibration (T-V) energy transfer and a shattering mechanism.