Collisional Deactivation of Ba 5d7p³D₁by Noble Gases^†

Collisional deactivation of the 5d7p D-3(1) state of Ba by noble gases is studied by time- and wavelength-resolved fluorescence techniques. A pulsed, frequency- doubled dye laser at 273.9 nm excites the 5d7p D-3(1) level from the around state, and fluorescence at 364.1 and 366.6 nm from the 5d7p D-3(1)-> 6s5d D-3(1) and 5d7p D-3(1) -> 6s5d D-3(2) transitions, respectively, is monitored in real time to obtain the deactivation rate constants. At 835 K these rate constants are as follows: He, (1.69 +/- 0.08) x 10(-9) cm(3) s(-1); Ne, (3.93 +/- 0.14) x 10(-10) cm(3) S-1; Ar, (4.53 +/- 0.15) x 10(-10) cm(3) S-1; Kr, (4.64 +/- 0.13) x 10(-10) cm(3) S-1; Xe, (5.59 +/- 0.22) x 10(-10) cm3 S-1. From time-resolved 5d7p 31), emission in the absence of noble gas and from the intercepts of the quenching plots, the lifetime of this state is determined to be 100 +/- 1 ns. Using time- and wavelength-resolved Ba emission with a low background pressure of noble gas, radiative lifetimes of several near-resonant states are determined from the exponential rise of the fluorescence signals. These results are as follows: 5d6d D-3(3), 28 +/- 3 ns; 5d7p P-3(1), 46 +/- 2 ns; 5d6d (3)G(3), 21.5 +/- 0.8 ns; 5d7p F-3(3), 48 +/- 1 ns. Integrated fluorescence signals are used to infer the relative rate constants for population transfer from the 5d7p D-3(1) state to eleven near-resonant fine structure states.