Caesium 6P fine-structure mixing and quenching induced by collisions with ground-state caesium atoms and molecules

Applying the cw laser fluorescence method, the cross sections for the fine structure mixing and quenching of the Cs 6P state, induced by collisions with ground-state caesium atoms and molecules, have been measured. Caesium atoms were optically excited to the 5DJ states via quadrupole-allowed 6S1/2 → 5DJ transitions, while the resonance states were populated by the radiative and collisional 5DJ → 6PJ transitions. The relative populations of the Cs 6PJ sublevels, as well as ratio of the 5D3/2 to 6P3/2 populations, were measured as a function of the caesium ground-state number density. From these measurements we obtained the cross section of (14 ± 5) × 10−16 cm2 at T = 585 K for the process Cs(6P1/2)→ Cs(6P3/2) induced by collisions with ground-state caesium atoms. The applied experimental approach enabled the determination of the effective spontaneous rates for the 6PJ states which are in agreement with the predictions of Holstein’s theory. The cross sections for quenching of 6PJ by caesium atoms and molecules were measured at T = 635 K and the obtained values are (1.6± 1.4)× 10−16 cm2 and (1210 ± 260) × 10−16 cm2, respectively. Using recently calculated Cs∗ + Cs potentials we performed an analysis which shows a good agreement between the measured values and the theoretical estimates.