Energy pooling from Ca[4s4p(3 P J )] and Ca[4s3d(1 D 2)] 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(3PJ)] 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 τe= 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 kCa=(4 ± 3)× 10–14 cm3 atom–1 s–1, in sensible accord with similar data for the quenching of Ca(4 3PJ) by the ground-state calcium atom. Energy pooling between Ca(4 3PJ)+ Ca(4 3PJ) 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.