CD4およびND3のガス-液体相互作用における選択性：水性フラット液体ジェットからの分子ビーム散乱

The dynamics of polar and nonpolar molecules colliding with an aqueous surface are characterized by scattering molecular beams of deuterated methane and ammonia, CD4 and ND3 (Ei = 28.9 and 30.3 kJ mol-1, respectively), from a flat liquid jet of cold salty water (8 m LiBr, 230 K). Translational energy distributions of scattered species collected as a function of collision geometry probe both impulsive scattering (IS) and thermal desorption (TD) mechanisms. We find that CD4 scattering is dominated by IS and exhibits a super-specular angular distribution. The fraction of TD scattering events is notably smaller for cold salty water than for dodecane, consistent with a higher free energy of solvation for CD4 in the water jet. In contrast, no scattering signal is seen for ND3 from the water jet, a result attributed to the high solubility and efficient protonation of ND3 in liquid water. The IS channel for CD4 was analyzed using a soft-sphere model, yielding a higher internal energy (Eint) and lower effective surface mass (meff) than was seen for Ne/water; the higher value of Eint is attributed to rotational excitation of the scattered CD4. These findings demonstrate that the outcomes of a gas-liquid collision-scattering trajectory, surface adherence, and energy transfer-are directed at the molecular level by both the gaseous scatterer and liquid surface.