Collisional quenching of Ca(4 3PJ) studied by time-resolved emission, 4 3P1→ 4 1S0+hν(λ= 657.3 nm), following dye-laser excitation

Abstract

We present a study of the collisional quenching of electronically excited calcium atoms, Ca[4s4p(³P_J)], 1.885 eV above the 4s²(¹S₀) ground state, by a range of added gases. Ca(4 ³P₁) was generated by repetitive pulsed dye-laser excitation at λ= 657.3 nm [Ca(4 ³P₁)â†� Ca(4 ¹S₀)] of calcium vapour in equilibrium with solid calcium at elevated temperatures (1000 K) in a slow flow system, kinetically equivalent to a static system. Following rapid Boltzmann equilibration within the 4 ³P_J manifold, the time-resolved forbidden emission, 4 ³P₁→ 4 ¹S₀+hν(λ= 657.3 nm), was monitored in the presence of added gases using ‘pre-trigger photomultiplier gating’ and boxcar integration. The following absolute second-order quenching constants (k_Q/cm³ molecule^–1 s^–1, 1000 K, errors 1σ) are reported: CO, 3.7 ± 0.5 × 10^–13; NO, 3.2 ± 0.3 × 10^–13; CO₂, 3.1 ± 0.3 × 10^–13; N₂O, 6.5 ± 0.5 × 10^–13; NH₃, 2.5 ± 0.3 × 10^–13; CH₄, 5.4 ± 0.4 × 10^–13; CF₄, 1.9 ± 0.2 × 10^–13; C₂H₂, 1.4 ± 0.2 × 10^–13; C₂H₄, 2.3 ± 0.3 × 10^–13; C₆H₆, 6.0 ± 0.2 × 10^–12. Where possible these data are compared with those derived from other decay measurements in which Ca(4 ³P_J) was generated by dye-laser excitation and monitored either via time-resolved atomic resonance absorption spectroscopy or by phase-shift techniques. The absolute rate constants are compared with analogous data for Mg(3 ³P_J)(2.71 eV) and discussed, where appropriate, in terms of orbital correlation and in relation to data from atomic beams which describe chemiluminescence from product states.