Rotationally inelastic collisions of LiH with He. III. Experimental determination of state-to-state cross sections

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Abstract
State-to-state rotationally inelastic cross sections for the scattering of 7LiH with helium have been determined by the use of electric quadrupole rotational state selection and dye laser fluorescence detection. Results for the incident j=1 state and final states j′=0, 2–15 at an average collision energy of 0.32 eV are reported. As a result of the finite angular acceptance of the laser detection zone and the observed dependence of the cross sections on the scattering path length l, the present values are lower limits to the absolute integral σj=1→j′ values. Because of the theoretical simplicity of the LiH–He system, comparison with accurate quantum calculations for the cross sections (see Papers I and II of this series) has been possible. Calculations using the coupled states dynamical approximation with an ab initio potential surface reproduce well the qualitative behavior of the experimental cross sections. Comparison with results from simpler theoretical models suggests that the accuracy of the potential energy surface employed is crucial for an adequate theoretical description of the dynamics.