Distinguishing Mechanisms for Reactive Uptake at Liquid Surfaces via Angular Distributions of Inelastically Scattered Molecules

Maksymilian J. Roman, Adam G. Knight, Daniel R. Moon, Paul D. Lane, Matthew L. Costen, Kenneth G. McKendrick*

*Corresponding author for this work

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Abstract

Angular distributions of OH inelastically scattered from the surfaces of the reactive hydrocarbon liquids squalane (fully saturated) and squalene (partially unsaturated) have been measured. A pulsed, rotationally cold molecular beam (Ei = 35 kJ mol-1) of OH was scattered from refreshed liquid surfaces in a vacuum. Spatially and temporally resolved OH number densities were measured by pulsed, planar laser-induced fluorescence. Results are compared with those for the inert liquid perfluoropolyether. The clearly asymmetric distributions for 45° incidence add to the weight of evidence for predominantly impulsive scattering from all three liquids. However, we propose that significant differences in their shapes may be diagnostic of contrasting reaction mechanisms. Direct, near-specular trajectories survive preferentially on squalene, consistent with an addition mechanism removing those at more backward angles. This trend is reversed for squalane, as expected for direct abstraction. The results reinforce the need to consider the effects of composition-dependent contributions from different reaction mechanisms in the modeling of OH-aging of atmospheric aerosol particles.

Original languageEnglish
Pages (from-to)5166–5174
Number of pages9
JournalThe Journal of Physical Chemistry A
Volume128
Issue number26
Early online date25 Jun 2024
DOIs
Publication statusPublished - 4 Jul 2024

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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