Studies of rotationally inelastic collisions of NaK and NaCs with Ar and He perturbers

We report studies of rotationally inelastic collisions of Ar and He atoms with the molecules NaK and NaCs prepared in various ro-vibrational levels of the $A\,^1\Sigma^+$ electronic state. We use laser induced fluorescence (LIF) and polarization labeling (PL) spectroscopy in a pump-probe, two step excitation process. The pump excites the molecule to a ro-vibrational level $(v,J)$ in the $A$ state. The probe laser is scanned over transitions to the $3\,^1\Pi$ state in NaK or the $5\,^3\Pi$ state in NaCs. In addition to strong direct lines, we observe weak satellite lines that arise from collision-induced transitions of the $A$ state level $(v,J)$ to $(v,J+\Delta J)$. The ratio of intensities of the satellite line to the direct line in LIF and PL yields information about population and orientation transfer. Preliminary results show a strong propensity for collisions with $\Delta J$=even for NaK; the propensity is larger for He than for Ar. Collisions of NaCs with He show a similar propensity, but collisions of NaCs with Ar do not. Theoretical calculations are also underway. For He-NaK, we have completed potential surface calculations using GAMESS and coupled channel scattering calculations of rotational energy transfer and transfer of orientation.