Rotationally inelastic collisions of He and Ar with NaK: Theory and Experiment

Rotationally inelastic collisions of NaK $A\,^1\Sigma^+$ molecules with He and Ar are studied. At Lehigh, we use pump-probe polarization labeling (PL) and laser-induced fluorescence (LIF) spectroscopy. At Lyon, Fourier transform (FT)-resolved LIF spectra are recorded. In both cases, the pump laser excites a particular ro-vibrational level $A\,^1\Sigma^+$($v, J$). We observe strong direct lines corresponding to transitions from the ($v, J$) level pumped, and weak satellite lines corresponding to transitions from collisionally-populated levels ($v, J^{\prime} = J + \Delta J$). The ratios of satellite to direct line intensities in LIF and PL yield population and orientation transfer information. A strong propensity for $\Delta J =$ even transitions is observed for both He and Ar perturbers. In the FT fluorescence experiment we also observe $v$-changing collisions. {\it Ab initio} potential surface and scattering calculations are underway for collisions in the $A\,^1\Sigma^+$ and $X\,^1\Sigma^+$ states. For He-NaK we have calculated potential surfaces using GAMESS and carried out coupled channel scattering calculations of transfer of population, orientation, and alignment. Calculations of $v$-changing collision cross sections are also in progress.