Quantum State Resolved 3D Velocity Map Imaging of Surface-Scattered Molecules: Incident Energy Effects in HCl + Self-Assembled Monolayer Collisions

Abstract

Thermal and hyperthermal HCl (v = 0, J = 0) collision dynamics at the surface of methyl-terminated self-assembled monolayers (SAMs) are probed by state-selective ionization followed by velocity-map imaging (VMI) to yield a full 2π steradian map of final 3D velocity distributions (vx, vy, vz) as a function of rovibrational (v, J) quantum state. “DC slicing” of the scattered HCl flux normal to the surface (vz) provides a powerful tool for eliminating incident beam contamination, as well as access to fully correlated, 3D flux weighted rovibrational quantum state + translational scattering dynamics in unprecedented detail. At low collision energies (Einc ≈ 0.7(1) kcal/mol), the scattering dynamics are completely dominated by trapping-desorption (TD) events, for which both external (i.e., translational) and internal (i.e., rovibrational) degrees of freedom quantitatively track the SAM surface temperature (TS). Hyperthermal scattering data at high collision energies (Einc ≈ 17(1) kcal/mol) provide direct eviden...