Time-resolved emission studies of the kinetic behaviour of Ca(4 3PJ) and Sr(5 3PJ) following pulsed dye-laser excitation. Electronic energy exchange between Ca(4 3PJ) and Sr(5 3Pj), energy pooling and decay measurements on Ca(4 3PJ), Sr(5 3PJ) and Sr(6 3S1)

Abstract

The kinetics of Ca(4 ³P_J), Sr(5 ³P_J) 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(4³P_J) manifold, fast, near-resonant energy transfer took place with Sr(5 ¹S₀) to yield Sr(5 ³P_J), 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 ³P_J)+ Sr(5 ¹S₀)⇌ Ca(4 ¹S₀)+ Sr(5 ³P_J) and its sustenance throughout kinetic decays. A further comparison of the first-order decay coefficients for the decays of Ca(4 ³P_J) and Sr(5 ³P_J) with those for Sr(6 ³S₁) demonstrated energy pooling between Ca(4 ³P_J)+ Sr(5 ³P_J) and Sr(5 ³P_J)+ Sr(5 ³P_J). Finally, the measured first-order decay coefficients, k′, for Ca(4 ³P_J) and Sr(5 ³P_J) in chemical equilibrium with one another are seperated quantitatively into their component parts of spontaneous emission, diffusion, the equilibrium constant connecting the ³P_J states and collisional quenching rate constants. Rate constants for quenching of Ca(4 ³P_J) and Sr(5 ³P_J) 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.