engleski

Energy pooling in barium with 6p P-1(1) state excitation

Energy-pooling collisions between low-lying excited states of Ba have been studied. We have used a cw dye laser to excite the $6p$ $^1P_1$ level in Ba. Radiative decay and collisions with Ba($6s^2$ $^1S_0$) or buffer-gas atoms (Ar, He) populate also the $6p$ $^3P_J$, $5d$ $^1D_2$ and $5d$ $^3D_J$ metastable levels. In addition we have found that the $5d$ $^3D_J$ and $5d$ $^1D_2$ metastable levels are populated when the laser is tuned into the blue from the 553.5 nm line under which conditions pronounced cone emission is observed. The spatial density distributions of these excited levels were measured by the absorption of lines from a Ba hollow--cathode lamp as a function of laser frequency. When the laser was on the exact atomic resonance we observed fluorescence from the $6p^{;prime};$ $^3D_J$, $6d$ $^3D_J$, $6p^{;prime};$ $^1P_1$, $7p$ $^1P_1$, $6p^{;prime};$ $^3P_J$, $7p$ $^3P_J$ and $7s$ $^3S_1$ states populated by energy--pooling collisions of Ba($6p$ $^1P_1$)+Ba($6p$ $^3P_J$, $5d$ $^{;1, 3};D$). For the cone emission laser resonance energy pooling towards lower states involving only metastable atoms in the entrance channel was observed. By changing the buffer gas pressure the fluorescence intensity ratio between $6d$ $^3D_J o 6p$ $ ^3P_2$ and $6p^{;prime};$ $^1P_1 o 5d$ $^1D_2$ transitions changes substantially. This is found to be due to redistribution of population among metastable levels, both in magnitude and space.

energy-pooling collisions; barium

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