The collisional quenching of Ca[4s4p(P-3(J))] by Ca[4s(2)(S-1(0))] following pulsed dye-laser excitation of atomic calcium

The collisional quenching of electronically excited calcium atoms, Ca[4s4p( P-3(J)), 1.888 eV above the 4s(2)(S-1(0)) ground state by ground state calc ium atoms, Ca[4s(2)(S-1(0))], has been investigated. Ca[4s4p(P-3(1))] was g enerated by the pulsed dye-laser excitation of ground state calcium atoms a t lambda=657.3 nm {Ca[4s4p(P-3(1))] <-- Ca[4s(2)(S-1(0))]} over a range of elevated temperatures in the presence of excess helium buffer gas. Measurem ents were then made of the atomic resonance fluorescence from Ca(4(3)P(1) - -> 4(1)S(0)) after Boltzmann equilibration within Ca(4(3)P(0.1.2)). First-o rder decay coefficients for the atomic emission profiles were quantified bo th as a function of temperature and hence, atomic density of Ca(4(1)S(0)) a nd of helium density itself. Consideration of the terms contributing to the measured decay coefficients, viz. emission, diffusion, and collisional que nching of Ca(4(3)P(J)) by Ca(4(1)S(0)) and He yields the collisional rate d ata. The absolute second-order rate constant for quenching of Ca(P-3) by Ca (S-1) is found to be k(Ca)=(2.4+/-0.3) x 10(-12) cm(3) per atom s(-1) (810- 997 K) marginally lower than obtained by phase angle modulation following d ye-laser excitation for a similar temperature range. It is significantly la rger than that obtained from earlier estimates derived from the departure o f a T-1.5 dependence of the temperature variation of the diffusion coeffici ent, D-12((CaP)-P-3-He), measured in the time-domain. A related analysis of the first-order decay coefficients for Ca(43PJ) yielded the rate constant for the collisional quenching of Ca(P-3) by He, viz. k(He)=(2.3+/-0.3)x 10( -16) cm(3) per atom s(-1) (T=940 K). This is in agreement with the upper li mit obtained earlier in the time-domain but significantly lower than that r esulting from phase angle modulation measurements across a temperature rang e in this region. (C) 2000 Elsevier Science S.A. All rights reserved.