Thermal-energy collisions of rubidium Rydberg states withN2molecules

The total depopulation cross sections by ${\mathrm{N}}_2$ of high rubidium Rydberg states, $\mathrm{Rb}\mathrm{}\left(\mathrm{ns}\right)\mathrm{} \mathrm{}(n=25-46\mathrm{})\mathrm{}$ and $\mathrm{Rb}\mathrm{}\left(\mathrm{nd}\right)\mathrm{} \mathrm{}(n=23-44\mathrm{})\mathrm{}$, have been measured using time-resolved field ionization technique and compared to previous results obtained on the quenching of $\mathrm{Rb}\mathrm{}\left(\mathrm{nl}\right)\mathrm{}$ by CO. It is shown that the $\mathrm{Rb}\mathrm{}\left(\mathrm{nl}\right)\mathrm{}$ depopulation by ${\mathrm{N}}_2$ is much less efficient than the $\mathrm{Rb}\mathrm{}\left(\mathrm{nl}\right)\mathrm{}$ depopulation by CO and leads mainly to the quasielastic process of angular momentum mixing via the short-range interaction between the quasifree Rydberg-state electron and the molecule. It is clearly demonstrated that the presence of a permanent dipole in CO changes the collisional processes drastically. The agreement between experimental and theoretical predictions based on the impulse approximation is quite satisfactory.