Development of Molecular Beam Double Resonance Spectroscopy by Use of Evanescent Wave and Study of Molecule-Solid Surface Interactions

点击翻译按钮获取中文摘要

We have carried out molecular beam spectroscopy and evanescent wave spectroscopy to study interactions between solid surface and molecules in the gas phase.Combination of the supersonic molecular beam technique and the infrared double resonance spectroscopy enables measurements of the probability of collision induced transitions between specific vibration-rotation states of molecules. First, the molecular beam double resonance method was tested In the measurement of the state-to-state cross section of the rotational transitions in NH_3 caused by the dipole-quadrupole interaction with nonpolar target molecules. Our experimental procedure has been justified because the obtained cross sections agree quite well with those nonempirically calculated from a collision theory.Then, we applied the method to observe collision-induced population change in the rotational states of NH_3 scattered from solid surfaces, such as glass, Al, and Au. It has been found that the selection rule in the dipole transition dominates the collision induced transition on glass surface. On the other hand, the molecule makes a hard collision with metal surfaces, and there is no definite selection rule.Simultaneously, we have developed a evanescent-wave laser spectrometer, and detected rotation-vibration spectra of NH_3 molecules close to NaCl surface. The spectral line of NH_3 near the surface was broadened approximately by 50 %, compared with that in the gas phase. The line width was proportional to the square root of the surface temperature. This may be attributed to the phase relaxation induced by the interaction with the solid surface.In the future, we are going to combine the molecular beam method with the evanescent wave spectroscopy for further research of the scattering process on solid surface.