Time-dependent study of the dynamics of the collision-induced intramultiplet mixing of Ca(4s4p( 3P J)) by helium at 750 K following pulsed dye-laser generation of Ca(4s4p( 3P 1))

Abstract

We present a kinetic study in the time-domain of the collisionally-induced intramultiplet mixing within Ca(4s4p( 3P J )), 1.888 eV above the 4s 2( 1S 0) electronic ground state. Ca(4s4p( 3P 1)) was generated by the pulsed dye-laser excitation of calcium vapour at λ=657.3 nm (Ca(4s4p( 3P 1))←Ca(4s 2( 1S 0)) at elevated temperature ( T=750 K). The time-dependent evolution of the concentrations of the individual spin-orbit states, Ca(4 3P 0,1,2), where the J=0–1 and 1–2 separations are 52.2 and 105.8 cm −1, were monitored in the presence of helium by laser-induced fluorescence fluorescence (LIF) of the 4s5s( 3S 1)-4s4p( 3P J ) transitions using a second dye-laser, delayed by means of varying optical path length. The resonance transitions at λ=610.3, 612,2 and 616.2 nm ( 3S 1- 3P 0,1,2, respectively) were normalized, to allow for variations in laser output, and monitored in the time regime 0–50 ns for pressures of He in the range 1–15 Torr, during which diffusion and spontaneous emission from Ca( 3P 1) could be totally neglected, the 3P 0,2 states being, so-called, “reservoir states”. The rate equations for [Ca( 3P 0,1,2)] were solved analytically and then convoluted numerically with the digitized forms of the 1S- 3P excitation laser and the LIF probe laser. Absolute rate data for the collisionally-induced spin-orbit processes in both directions, J=2-1, 1-0, 2-0, and the reverse, are reported. These results, determined from concentration profiles for Ca( 3P 0,1,2) determined in the time-domain for fixed pressures of He, are compared with analogous cross section data for Ca( 3P J )+He determined from molecular beams using J state selection optical pumping laser methods at a fixed time with varying low pressures of He and also with the results of recent quantum close-coupling calculations.