Energy pooling from Ca[4s4p(3PJ)] and Ca[4s3d(1D2)] studied by time-resolved atomic emission following pulsed dye-laser excitation

Abstract

Two separate series of investigations have been carried out on the optically metastable states Ca[4s4p(³P_J)] and Ca[4s3d(¹D₂)], generated by pulsed dye-laser excitation at λ= 657.3 nm {Ca[4s4p(³P₁)]â†� Ca[4s²(¹S₀)]} and λ= 457.5 nm {Ca[4s3d(¹D₂)]â†� Ca[4s²(¹S₀)]}, with particular emphasis on energy pooling. The kinetic behaviour of these two states has been characterised in detail across a wide range of temperature and pressure by time-resolved atomic emission measurements at the resonance wavelengths. In the case of Ca[4s3d(¹D₂)] these represent the first time-resolved measurements on this atomic state, yielding a mean radiative lifetime for emission to all lower states of τ_e= 1.71 ± 0.03 ms, in accord with time-of-flight measurements in atomic beams. The measured temperature dependence of the diffusion coefficient D₁₂[Ca(4 ¹D₂)–He], when expressed in the form D₁₂∝Tⁿ, yielded n= 1.77 ± 0.08. Further, the rate constant for the collisional quenching of Ca(4 ¹D₂) by Ca(4 ¹S₀) itself is estimated to be k_Ca=(4 ± 3)× 10^–14 cm³ atom^–1 s^–1, in sensible accord with similar data for the quenching of Ca(4 ³P_J) by the ground-state calcium atom. Energy pooling between Ca(4 ³P_J)+ Ca(4 ³P_J) is shown to give rise directly to Ca[4s4p(¹P₁)] and Ca[4s3d(¹D₂)]. Energy pooling between Ca(4 ¹D₂)+ Ca(4 ¹D₂) is shown to yield 22 electronic states, each of whose kinetic behaviour was characterised quantitatively from the relevant atomic emission profiles, including measurement of relative atomic yields.