Collisionally induced intramultiplet mixing of Sr(5(3)P(J)) metastable states by He, Ar and Sr ground state atoms

Intramultiplet collisionally induced mixing within the Sr[5s5p(P-3(0,1,2))] manifold is investigated by time-resolved laser-induced fluorescence (LIF) following the pulsed dye-laser generation of Sr(P-3(1)) of the electronic ground state {Sr[5s5p(P-3(0,l,2))] <-- Sr[5s(2)(S-1(0))], <lambda> = 689.26 nm} at elevated temperatures. The population profiles of the three spin-or bit states were individually monitored by LIF as well as that of Sr(P-3(1)) by spontaneous emission at the resonance wavelength. A kinetic model is em ployed that enables the process of spontaneous emission from Sr(P-3(1)) to be isolated initially and characterised by experiment. Particular emphasis is placed on the modelling procedure itself in which the separate kinetic c omponent due to spontaneous emission and the positions of the maxima in the P-3(0) and P-3(2) population profiles constitute severe constraints on the model. The collisional components within the model are reduced to three ra te constants where pairs of J states are connected in this context by detai led balance. Thus k(10) and k(12). and, by detailed balance, k(01) and k(21 ) are quantified at various temperatures and pressures to yield the absolut e value of these collision properties for Sr(P-3(j)) with He and Ar. Rate d ata for collisionally induced intramultiplet mixing in Sr(P-3(j)) by Sr(S-1 (0)) itself is also reported found to proceed at close to unit collisional efficiencies in all cases. Thus, at elevated temperatures, variations in at omic profiles are dominated by the differing vapour pressures of atomic str ontium. Estimates of the activation energies associated with k(10) and k(12 ) for the noble gases observed against this large competing background are found to be of the order of the spin-orbit splittings. The model overall is found to be insensitive to k(02) and k(20) whose magnitudes are small by c omparison with those for the collisional rate data connecting adjacent J st ates. Whilst collisional processes for He are some two orders of magnitude more efficient than those for Ar, all of these are seen to be 'adiabatic', in contrast with the gas kinetic rate constants of ground Sr, considered to be 'sudden' in character. The results are compared with analogous data der ived by atomic resonance absorption spectroscopy following pulsed generatio n of Sr(P-3(1)) and are considered in the context of theoretical calculatio ns employing quantum close coupling calculations. (C) 2001 Elsevier Science B.V. All rights reserved.