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Population and deactivation of lowest lying barium levels by collisions with He, Ar, Xe and Ba ground state atoms

Excitation transfer between the barium low lying excited states 6s6p 3P10, 6s5d l.D2 and 6s5d 3DJ bJy collisions with He, Ar, Xe and Ba has been investigated. The population densities in all levels involved were probed by absorption or by fluorescence using cw lasers. The depopulation cross sections of the Ba 3P10 state by collisions with noble gases were found to be sigma-He(3P10) = 5.5x10^(-16) cm^2, sigma-Ar(3P10) = 4.6x10^(-16) cm^2 and sigma-Xe(3P10) = 1.7x10^(-16) cm^2. For Ar, the collisional depopulation of the 3P10 level is exclusively due to the transition to the 1D2 state. Under the assumption that the 3DJ metastable states are populated collisionally by 1D2 -> 3DJ transfer only, we have deduced the upper limit for the corresponding cross section sigma-Ar13 = 1.3x10^(-18) cm^2. From the Ba 1D2 and Ba 3DJ steady-state diffusion distributions, collisional relaxation rates of the 1D2 and 3DJ levels were evaluated. The collisional relaxation rates by Ar and Ba yielded total cross sections for the depopulation of metastable levels: sigma-Ar(1D2) = 1.5x10^(-17) cm^2, sigma-Ba(1D2) ~ 1.0x10^(-13) cm^2., sigma-Ar(3DJ) = 7x10^(-21) cm^2., and sigma- Ba(3DJ) = 1x10^(-15) cm^2.. Furthermore, it was found that the main contribution of the colIisiona1 depopulation of the 1D2 state by Ar is related to back transfer to the 3PJ0 stae, whereas the deactivation of the 3DJ metastable state is due to back transfer to the 1D2 state. Taking into account other cross sections reported in literature we can conclude that collisional deactivation of both metastable levels by Ba ground state atoms can be attributed to their mutual collisional mixing.

excitation energy transfer ; barium ; metastable states

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