THE COLLISION CROSS-SECTIONS FOR THE FINE-STRUCTURE MIXING OF CESIUM 6P LEVELS INDUCED BY COLLISIONS WITH POTASSIUM ATOMS

The cross section for the fine-structure excitation transfer CS(6P(1/2 )) --> Cs(6P(3/2)), induced by collisions with the ground state potass ium atoms, has been measured by resonant Doppler-free two-photon spect roscopy. The population densities of caesium 6P(J) (J = 1/2, 3/2) leve ls were probed by thermionic detection of the collisionally ionized ca esium atoms from the Cs(6P(J)) --> Cs(10S(1/2)) excitation channel. Th e cross section for the transfer process at the temperature T = 503 K has been found to be sigma(1/2 --> 3/2) = 45 Angstrom(2) +/- 20%. The result is compared with previously published experimental cross sectio ns for fine-structure transfer in resonance states of other alkali ele ments perturbed by potassium and a thoeretical value of the Li(2P(J))- K system calculated in a simple approach.