Angle-resolved molecular beam scattering of NO at the gas-liquid interface

作者：Zutz Amelia; Ne**itt David J^*

来源：Journal of Chemical Physics, 2017, 147(5): 054704.

DOI：10.1063/1.4995446

This study presents first results on angle-resolved, inelastic collision dynamics of thermal and hyperthermal molecular beams of NO at gas-liquid interfaces. Specifically, a collimated incident beam of supersonically cooled NO ((2)Pi(1/2), J = 0.5) is directed toward a series of low vapor pressure liquid surfaces ([bmim][Tf2N], squalane, and PFPE) at theta(inc) = 45(1)degrees, with the scattered molecules detected with quantum state resolution over a series of final angles (theta(s) = fi 60 degrees, fi 30 degrees, 0 degrees, 30 degrees, 45 degrees, and 60 degrees) via spatially filtered laser induced fluorescence. At low collision energies [E-inc = 2.7(9) kcal/mol], the angle-resolved quantum state distributions reveal (i) cos(theta(s)) probabilities for the scattered NO and (ii) electronic/rotational temperatures independent of final angle (theta(s)), in support of a simple physical picture of angle independent sticking coefficients and all incident NO thermally accommodating on the surface. However, the observed electronic/rotational temperatures for NO scattering reveal cooling below the surface temperature (T-elec < T-rot < T-S) for all three liquids, indicating a significant dependence of the sticking coefficient on NO internal quantum state. Angle-resolved scattering at high collision energies [E-inc = 20(2) kcal/mol] has also been explored, for which the NO scattering populations reveal angle-dependent dynamical branching between thermal desorption and impulsive scattering (IS) pathways that depend strongly on theta(s). Characterization of the data in terms of the final angle, rotational state, spin-orbit electronic state, collision energy, and liquid permit new correlations to be revealed and investigated in detail. For example, the IS rotational distributions reveal an enhanced propensity for higher J/spin-orbit excited states scattered into near specular angles and thus hotter rotational/electronic distributions measured in the forward scattering direction. Even more surprisingly, the average NO scattering angle () exhibits a remarkably strong correlation with final angular momentum, N, which implies a linear scaling between net forward scattering propensity and torque delivered to the NO projectile by the gas-liquid interface. Published by AIP Publishing.

• 出版日期2017-8-7