Fine structure excitation transfer between the lithiumD-lines by collisions with cesium atoms

Applying resonant Doppler-free 2-photon laser spectroscopy with thermionic diode detection, the cross sections for the excitation energy transfer of the collisional process⁷Li*(2P _1/2+Cs(6S _1/2)→⁷Li*(2P _3/2)+Cs(6S _1/2) have been measured. The experimental cross sections, σ^Li-Cs (1/2→3/2)=890 Ų and σ^Li-Cs (3/2→1/2)=430 Ų, are compared with theoretical data obtained by a sudden impact approximation approach taking into account the long-range interaction potentials only. The calculated cross sections show an excitation mixing process at large internuclear distances where Li-Cs dipole-dipole and dipole-quadrupole interaction forces are predominant.