| Detection of the rotational state distribution, angular momentum alignment, and the angular momentum orientation of N{dollar}sb2{dollar} scattering off Ag(111) is a sensitive probe of the potential energy surface (PES) of this system. Although all the molecules scattering off a surface are affected by the same PES, the forces exerted onto the molecule depend upon four initial conditions: the incident velocity vector, the two-dimensional impact parameter, the molecular orientation, and the energies and positions of the surface atoms. To differentiate between the effects of these four initial conditions, one can probe the anisotropy of the angular momentum of the scattered particles because these measurements are sensitive to the anisotropy in the PES. Both 2 + n resonantly enhanced multiphoton ionization (REMPI) and 1 + 1 laser induced fluorescence (LIF) can be employed to detect the angular momentum orientation and alignment. Formulas have been derived which enable polarization moments, the expectation values of angular momentum operators, to be extracted from raw polarization data taken with either REMPI or LIF. By converting polarization data into polarization moments, experiments can be compared with theory and, hence, the dynamics of a process can be investigated. For normal incident, rotationally cold N{dollar}sb2{dollar} scattering off cold Ag(111), the variation of the angular momentum orientation with both the exit angle and the rotational state indicate that the dominant initial condition in determining the exit angle is the two-dimensional impact parameter. However, the dominant initial condition in determining the rotational state and angular momentum orientation is the molecular orientation geometry. For glancing incident, rotationally cold N{dollar}sb2{dollar} scattering off hot Ag(111), the variations of the rotational populations and angular momentum polarization with exit angle indicate that raising the surface temperature causes a large broadening of the exit angles for a given initial molecular orientation geometry and two-dimensional impact parameter. Raising the surface temperature also appears to increase the in-plane forces that the surface exerts on the gas molecules. |
