Optimizing the Accuracy of Molecular Cross Sections and Rate Constants

We present a comprehensive, two-pronged approach to determining inelastic rate constants in rare gas collisions with laser-excited lithium dimer. In order to achieve the highest accuracy, we divided the work into a rigorous computational validation and a high-precision experimental study. 

In the computational section, we address the failure of the standard quasiclassical trajectory (QCT) methods to satisfy microscopic reversibility and detailed balance at low initial rotational levels. Through comparison with accurate quantum close-coupled calculations on ab initio potentials, we find that a symmetrical binning approach largely eliminates this failure for rotationally inelastic scattering. However, the vibrationally inelastic channel requires a different approach.  

Experimentally, we use laser-induced fluorescence spectroscopy to determine level-to-level rate constants. We have reevaluated our analysis process to give the most accurate rate constants for the inelastic processes under consideration. This two-pronged approach serves as an internal consistency check for computational and experimental methods used to measure molecular cross sections and rate constants and can be extended to situations in which the calculation of exact quantum mechanical cross sections is impractical.