Correlated Angular and Quantum State-Resolved CO2 Scattering Dynamics at the Gas−Liquid Interface

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 112; no. 39; pp. 9324 - 9335
• Main Authors: Perkins, Bradford G, Nesbitt, David J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.10.2008
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp8022887

Molecular beam scattering dynamics at the gas−liquid interface are investigated for CO2 (E inc = 10.6(8) kcal/mol) impinging on liquid perfluoropolyether (PFPE), with quantum state (v, J) populations measured as a function of incident (θinc) and final (θscat) scattering angles. The internal state distributions are well-characterized for both normal and grazing incident angles by a two-component Boltzmann model for trapping desorption (TD) and impulsive scattering (IS) at rotational temperatures T rot(TD/IS), where the fractional TD probability for CO2 on the perfluorinated surface is denoted by TD and IS densities (ρ) as α = ρTD/(ρTD + ρIS). On the basis of an assumed cos(θscat) scattering behavior for the TD flux component, the angular dependence of the IS flux at normal incidence (θinc = 0°) is surprisingly well-modeled by a simple cos n (θscat) distribution with n = 1.0 ± 0.2, while glancing incident angles (θinc = 30°, 45°, and 60°) result in lobular angular IS distributions scattered preferentially in the forward direction. This trend is also corroborated in the TD fraction α, which decreases rapidly under non-normal incident conditions as a function of backward versus forward scattering direction. Furthermore, the extent of rotational excitation in the IS channel increases dramatically with increasing angle of incidence, consistent with an increasing rotational torque due to surface roughness at the gas−liquid interface.