UC Berkeley

A newly designed molecular beam scattering apparatus that utilizes a flat liquid jet to study chemical reactions at the gas-liquid interface is reported. The flat liquid surface combined with a rotatable mass spectrometer that provides energetic, mass and angular selectivity allows for unprecedented insights into this highly relevant chemical interface. To provide a proof of feasibility for studying volatile liquid systems, experiments are performed on dodecane evaporation as well as dodecane as a scattering target for neon beams.In the first part of this dissertation, the evaporation of neon and dodecane from a neon-doped dodecane flat jet running inside vacuum is investigated. We demonstrate that it is possible to observe sensible velocity and angular distributions using this flat jet setup. The effect of near-surface vapor interactions with evaporating particles is observed by comparing dodecane and Ne evaporation, where both particles show different collision cross sections with the vapor. The angular distribution for both particles also follows the cosine distribution, which has been investigated in gas desorption from solid surfaces. Then, further exploration of neon scattering off the dodecane surface at varying incident translational energies and angles is performed. We demonstrate how the energy and angular sensitivity of our apparatus provides complete information to map out energetic processes at the liquid interface. Energy loss of the scattered neon atoms can be attributed to excitation of liquid surface modes and is well described by a “soft-sphere” kinematic model, from which we infer effective surface masses and total internal excitation from the collision during the collisional timescale. We believe that our results demonstrate the high potential of flat liquid jet scattering with regards to studying dynamics at the gas-liquid interface. By extending the experiment to water, which is planned for future experiments, we are opening up new experimental opportunities that are highly relevant to water-based catalysis and atmospheric chemistry.