Time-resolved resonance fluorescence studies of ground state phosphorus atoms, P[3p3(4S)]

Abstract

The temporal behaviour of ground state phosphorus atoms, P[3p³(⁴S)], generated by repetitive pulsed irradiation in a flow system, has been studied by time-resolved resonance fluorescence. P(3⁴S) was generated photochemically from PCI₃ in the presence of excess helium buffer gas and optically excited by means of the emission from a microwave-powered atomic spectroscopic source. The total resonance fluorescence in the vacuum ultraviolet from the systems P[3p²4s(⁴P_½,,5/2)→ 3p³(⁴S)](λ= 178.77, 178.29 and 177.50 nm, respectively) and P[3p⁴(⁴P_5/2,,½)→ 3p³(⁴S)](λ= 167.97, 167.46 and 167.17 nm, respectively) was monitored photoelectrically and the signal-averaged results employed to characterise the kinetic decay of the phosphorus atom in the presence of various added gases. An empirical calibration of the relationship between the fluorescence intensity and the relative particle density of P(3⁴S) was established and the linear region employed for kinetic study. Second-order rate constants (k_R, cm³ molecule^–1 s^–1, 300 K) are reported for the reaction of P(3⁴S) with the following gases: O₂(2.1 ± 0.3 × 10^–12), Cl₂(3.4 ± 0.3 × 10^–12), NO (5.3 ± 0.5 × 10^–13), C₂H₂(1.2 ± 0.1 × 10^–13), C₂H₄(6.8 ± 0.8 × 10^–13) and PCl₃(1.7 ± 0.3 × 10^–12). These data are compared with previous results obtained by time-resolved resonance line absorption and used to consider further the modified Beer–Lambert law, I_tr=I₀ exp [–ε(cl)^γ] used in the resonance absorption measurements. Finally, radiation trapping calculations are described for the systems P[3p²4s(⁴P_J)] and P[3p⁴(⁴P_J)]→ P[(3⁴S)] using the diffusion theory of radiation. Line shapes employing the summation of Voigt profiles for all the nuclear hyperfine components contributing to a given electronic transition are used. The calculated relationships between the fluorescence intensity and P[(3⁴S)] for various boundary conditions of the diffusion equation are compared with the empirical calibration.