Time-resolved emission studies of the kinetic behaviour of Ca(4 3 P J ) and Sr(5 3 P J ) following pulsed dye-laser excitation. Electronic energy exchange between Ca(4 3 P J ) and Sr(5 3 P j ), energy pooling and decay measurements on Ca(4 3 P J ), Sr(5 3 P J ) and Sr(6 3 S 1)

Abstract

The kinetics of Ca(4 3PJ), Sr(5 3PJ) and Sr(6 3S1) have been studied by time-resolved emission following pulsed dye-laser excitation. Ground-state calcium atoms, Ca[4s2(1S0)], in the presence of Sr[5s2(1S0)], were optically excited to the first electronically excited state, Ca[4s4p(3P1)], by means of a dye-laser operating at λ= 657.3 nm [Ca(4 3P1)â†� Ca(4 1S0)]. Following rapid Boltzmann equilibration within the Ca(43PJ) manifold, fast, near-resonant energy transfer took place with Sr(5 1S0) to yield Sr(5 3PJ), together with energy pooling to yield Sr(6 3S1). The following transitions were monitored in the time-resolved mode using pre-trigger photomultiplier gating and boxcar integration with repetitive pulsing on a slow-flow system, kinetically equivalent to a static system: Ca(4 3P1)→ Ca(4 1S0)+hν(λ= 657.3 nm), Sr(5 3P1)→ Sr(5 1S0)+hν(λ= 689.3 nm) and Sr(6 3S1)→ Sr(5 3P0)+hν(λ= 679.1 nm). Detailed measurements of the time dependence of the emission profiles at λ= 657.3 and 689.3 nm demonstrated the rapid establishment of the equilibrium Ca(4 3PJ)+ Sr(5 1S0)⇌ Ca(4 1S0)+ Sr(5 3PJ) and its sustenance throughout kinetic decays. A further comparison of the first-order decay coefficients for the decays of Ca(4 3PJ) and Sr(5 3PJ) with those for Sr(6 3S1) demonstrated energy pooling between Ca(4 3PJ)+ Sr(5 3PJ) and Sr(5 3PJ)+ Sr(5 3PJ). Finally, the measured first-order decay coefficients, k′, for Ca(4 3PJ) and Sr(5 3PJ) in chemical equilibrium with one another are seperated quantitatively into their component parts of spontaneous emission, diffusion, the equilibrium constant connecting the 3PJ states and collisional quenching rate constants. Rate constants for quenching of Ca(4 3PJ) and Sr(5 3PJ) by Kr, Xe, H2 and D2 derived from earlier measurements on the individual atoms are found to be quantitatively consistent with the decay profiles under equilibrium conditions.