Gas surface interactions studied with state-prepared molecules

The interaction of gas-phase molecules with solid surfaces is complicated by the many molecular and surface degrees-of-freedom (DOFs) which may affect the scattering process. This review covers experimental work in which the quantum state populations of molecules incident on a surface are prepared or selected in some manner, and the scattering of these prepared molecules is followed. Experiments are discussed in which essentially all (electronic, vibrational, rotational, and translational) molecular DOFs are controlled. Two main techniques to produce a flux of state-prepared molecules for surface studies have been developed; both are natural extensions of existing gas-phase scattering work. The first employs direct optical excitation and relies on the associated selection rules to generate population in a desired state. The second uses inhomogeneous electric or magnetic fields as a filter to transmit a particular state and reject others. Specific applications of each of these techniques are reviewed with emphasis placed on the insight gained from the quantum state specific nature of the incident molecules.