ENERGY POOLING TO THE BA 6S6P P-1(1)0 LEVEL ARISING FROM COLLISIONS BETWEEN PAIRS OF METASTABLE BA 6S5D D-3(J) ATOMS

The energy-pooling rate coefficient for the Ba(6s5d D-3(j)) + Ba(6s5d D-3(j)) --> Ba(6s(2 1)S(0)) + Ba(6s6p P-1(1)0) process has been measur ed. The barium atoms were excited by a cw diode laser tuned to the fre quency of the 791.3 nm intercombination line and the metastable atoms in the 6s5d D-3(j) State were produced due to radiative and collisiona l depopulation of the laser-excited 6s6p P-3(1)0 state. The measuremen ts were performed at Ba-133 number densities of about 4 x 10(10) cm(-3 ) and at 30 mbar argon as the buffer gas. Most of the barium ground st ate atoms in the excitation zone were transferred to the triplet metas table state at the laser pump power applied. The energy pooling rate c oefficient was determined by comparing the fluorescence intensity of t he barium 553.6 nm resonance line and the fluorescence intensity of th e intercombination line 791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single mode ring dye laser. The rate coefficient was found to be k = 1 x 10(-10) cm(3) s(-1) at T = 730 K.