Time-resolved emission studies of the collisional quenching of Ca(4 3PJ) and Sr(5 3PJ) by various gases in an equilibrium-coupled system following pulsed dye-laser excitation at λ= 657.3 nm [Ca(4 3P1)â†� Ca(4 1S0)]

Abstract

The collisional quenching of Ca(4 ³P_J) and Sr(5 ³P_J) has been studied for an equilibrium system coupled by the process Ca(4 ³P_J)+ Sr(5 ¹S₀)⇌ Ca(4 ¹S₀)+ Sr(5 ³P_J) and established following pulsed dye-laser excitation of Ca(4 ¹S₀) to Ca(4 ³P₁) at λ= 657.3 nm in mixtures of calcium and strontium vapour in the presence of an excess of helium buffer gas and added quenching gases. Ca(4 ³P₁), Sr(5 ³P₁) and Sr(6 ³S₁) were monitored by time-resolved emission at λ= 657.3, 689.3 [Sr(5 ³P₁)→ Sr(5 ¹S₀)+hν) and 679.1 nm [Sr(6 ³S₁)→ Sr(5 ³P₀)+hν], respectively, using boxcar integration. The measured first-order decay coefficients for Ca(4 ³P_J) and Sr(5 ³P_J) under equilibrium-coupled conditions were found to be in quantitative agreement with previously measured values of absolute second-order rate constants for the quenching gases Kr, Xe, H₂, D₂, N₂, CO, NO, N₂O, CO₂, NH₃, CH₄, CF₄, C₂H₂, C₂H₄ and C₆H₆, obtained using the present system, employing signal averaging, on decays of Ca(4 ³P_J) and Sr(5 ³P_J) individually. Finally, energy pooling according to the processes Ca(4 ³P_J)+ Sr(5 ³P_J)→ Sr(6 ³S₁)+ Ca(4 ¹S₀), Sr(5 ³P_J)Sr(5 ³P_J)→ Sr(6 ³S₁)+ Sr(5 ¹S₀) was investigated quantitatively from measurements at λ= 679.1 nm in the time domain and in the presence of the quenching gases.