Collisional quenching of electronically excited strontium atoms, Sr(5 3PJ), studied by time-resolved emission at λ= 689.3 nm (5 3P1→ 5 1S0+hν) following dye-laser excitation

Abstract

The collisional quenching of electronically excited strontium atoms, Sr[5s5p(³P_J)], 1.8 eV above the 5s²(¹S₀) ground state has been studied in the presence of a wide range of added gases. Sr(5 ³P₁) was generated by the repetitive pulsed dye-laser excitation of strontium vapour at λ= 689.3 nm [Sr(5 ³P₁)â†� Sr(5 ¹S₀)] and monitored photoelectrically using pretrigger photomultiplier gating and boxcar integration by time-resolved forbidden emission at the resonance wavelength subsequent to collisionally induced Boltzmann equilibration within Sr(5 ³P_J). The following absolute second-order quenching rate constants (k)/cm³ molecule s^–1, T= 950 K, errors 1 σ) are reported: N₂, (3.2 ± 0.2)× 10^–11; CO, (2.0 ± 0.1)× 10^–11; CO₂, (1.3 ± 0.1)× 10^–11; N₂O, (1.5 ± 0.2)× 10^–11; NH₃, (2.2 ± 0.1)× 10^–11; CH₄, (1.0 ± 0.2)× 10^–12; CF₄, (7.8 ± 07.)× 10^–13; C₂H₂, (1.3 ± 0.1)× 10^–11; C₂H₄, (4.2 ± 0.3)× 10^–10; C₆H₆, (2.4 ± 0.2)× 10^–10. These constitute the first body of absolute collisional rate data reported for Sr(5 ³P_J) with these gases and are compared with analogous data reported hitherto for Mg(3 ³P_J) and Ca(4 ³P_J. In general terms, collisional quenching of Sr(5 ³P_J) by a given gas is considerably more efficient than for either Mg(3 ³P_J) or the similarly energized Ca(4 ³P_J)(1.8 eV). In the cases of CO₂ and N₂O, the rate data are considered in terms of chemical reaction to product states on the basis of symmetry arguments using C_s symmetry in the collision complex and the weak spin–orbit coupling approximation.