Kinetic investigation of electronic energy transfer processes following the pulsed dye-laser generation of excited atomic barium, Ba[6s6p(1P1)], in the presence atomic strontium

The collisional behaviour of Ba[6s5d(D-3(J))], 1.151 eV above the 6S(2)(1S(0)) electronic ground state, in the presence of atomic strontium, has been investigated in the 'long-time domain' (ca. 100 mu s-1 ms) following the pulsed dye-laser excitation of barium vapour at elevated temperature at lambda=553.5 nm (Ba[6s6p(P-1(1))] <--Ba[6s(2)(S-1(0))]. Ba(D-3(J)) is subsequently produced from the short-lived P-3(1) state (tau(e) = 8.37 +/- 0.38 ns) by a number of radiative and collisional processes. It may then be monitored in the 'long-time domain' by atomic spectroscopic marker methods involving either collisional activation of Ba(D-3(J)) by Ba(S-1(0)) and He buffer gas to yield Ba[6s6p(P-3(J))] with subsequent emission from the P-3(1) State (tau(e) = 1.2 +/- 0.1 mu s): Ba[6s6p(P-3(1))] -->Ba[6s(2)(S-1(0))] + hv (lambda = 791.1 nm). Alternatively, emission from Ba(P-1(1)) may be monitored at long times following the generation of this short-lived state by energy pooling following self-annihilation of Ba(D-3(J)) + Ba(D-3(J)) from Ba[6s6p(P-1(1))] --> Ba[6s(2)(S-1(0))] + hv (lambda = 553.5 nm). The generation of Ba(D-3(J)) in the presence of atomic strontium yields emission in the long-time domain from Sr[5s5p(P-3(1))] (tau(e) = 19.6 mu s): Sr[5s5p(P-3(1))] -->Sr[5s(2)(S-1(0))] + hv (lambda = 689.3 nm). Whilst the decay profiles at short times are complex in form, at long times all these atomic profiles show first-order kinetic removal with the decay coefficients for lambda = 791.1 nm, 689.3 nm and 553.5 nm emissions in the ratio 1 : 2 : 2, consistent with overall third-order activation of the form: Ba(D-3(J)) + Ba(D-3(J)) + Sr(S-1(0)) --> Sr(P-3(J)) + 2Ba(S-1(0)). The mechanism is modelled in detail, including measurement of integrated emission intensities, yielding kinetic data for fundamental collisional processes. The overall rate constant for the third-order collisional activation of Sr[5s5p(P-3(J)]) from 2Ba[6s5d(D-3(J))] + Sr[5s(2)(S-1(0))] takes the upper limit of 5.8 x 10(-27) cm(6) atom(-2) s(-1) (T= 900 K). The rate constant for the two body collisional quenching of Ba[6s5d(D-3(J))] by ground state atomic strontium, Sr[5s(2)(S-1(0))], is found to be (2.0 +/- 0.1) x 10(-12) cm(3) atom(-1) s(-1) (T = 900 K). (C) 1999 Elsevier Science S.A. All rights reserved.