[Collisional excitation transfer between Cs2 (B 1IIu) and Cs(6S)]

With a Cs density of -10(15) cm(-3) and typically -2% Cs2, cesium vapor was irradiated in a glass fluorescence cell with pulses of radiation from a YAG-laser- pumped OPO laser, populating Cs2 (B 1IIu) state by one-photon absorption. Predissociation of the B 1IIu state and energy transfer in Cs2 (B 1IIu)+Cs(6S) collisions were studied using methods of atomic and molecular fluorescence. The B 1IIu (v < 10) state does not predissociate in Cs vapor excited at lambda = 736 nm. The decay signal of the time-resolved fluorescence from the B 1IIu --> X 1sigma(g)+ transition was monitored. According to the Stern-Volmer equation, a plot of reciprocal of effective lifetimes of the Cs2 (B 1IIu) state quenched by Cs(6S) atoms against its densities yielded a slope that indicated the total cross section for deactivation and an intercept(at which the Cs pressure is zero) that provided the information on the radiative lifetime of the state. The radiative lifetime is (35 +/- 7)ns for the B 1IIu state. The total cross section for deactivation of excited Cs2 [B 1IIu (v < 10)] molecules by means of collisions with Cs atoms is (4.0 +/- 0.5) x 10(-14) cm2. The B 1IIu (v > 30) state pre-dissociates in Cs vapor excited at lambda = 705 nm. At the different Cs densities, the relative time-integrated intensities of the resulting Cs emission lines, I(6P1/2 --> 6S1/2) [I(D1)] and I(6P3/2 --> 6S1/2) [I(D2)], and Cs2 (B 1IIu) band-pass (725 --> 735 nm) I[Cs2 (B 1IIu)] were measured. By combining Cs 6P fine-structure mixing and quenching induced by collisions with ground Cs atoms, the authors obtained absolute values for predissociation and collisional transfer cross sections. The predissociation rates are (4.3 +/- 1.7) x 10(6) s(-1) (for predissociating to 6P3/2) and (4.7 +/- 1.9) x 10(6) s(-1) (for predissociating to 6P1/2), respectively. The collisional transfer cross sections are (0.45 +/- 0.18) x 10(-14) cm2 (for transfering to 6P1/2) and (4.3 +/- 1.7) x 10(-14) cm2 (for transfering to 6P3/2). These experimental results show that if Cs2 excited state is predissociation state, it can produce Cs(6P) atoms by predissociation and collisional transfer; if Cs2 excited state is bound, it can produce produce Cs(6P) atoms by collisional transfer.