Molecular beam scattering of ammonia from a dodecane flat liquid jet

Abstract

The evaporation and scattering of ND₃ from a dodecane flat liquid jet are investigated and the results are compared with previous studies on molecular beam scattering from liquid surfaces. Evaporation is well-described by a Maxwell–Boltzmann flux distribution with a cos θ angular distribution at the liquid temperature. Scattering experiments at E_i = 28.8 kJ mol⁻¹ over a range of deflection angles show evidence for impulsive scattering and thermal desorption. At a deflection angle of 90°, the thermal desorption fraction is 0.49, which is higher than that of other molecules previously scattered from dodecane and consistent with work performed on NH₃ scattering from a squalane-wetted wheel. ND₃ scattering from dodecane results in super-specular scattering, as seen in previous experiments on dodecane. The impulsive scattering channel is fitted to a “soft-sphere” model, yielding an effective surface mass of 55 amu and an internal excitation of 5.08 kJ mol⁻¹. Overall, impulsively scattered ND₃ behaves similarly to other small molecules scattered from dodecane.