Kinetic study of ground state phosphorus atoms, P(34S), by atomic absorption spectroscopy in the vacuum ultraviolet

Abstract

A kinetic study of ground state phosphorus atoms is presented. P(3⁴S) was generated by the repetitive pulsed irradiation of low pressures of PCl₃ in the presence of excess helium buffer gas and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation in the vacuum ultraviolet. The three resonance lines associated with the 4s(⁴P) state were all employed for kinetic measurements, namely, 4s(⁴P_5/2)– 3p³(⁴S)(λ= 177.50 nm), 4s(⁴P)– 3p³(⁴S)(λ= 178.29 nm) and 4s(⁴P_1/2)– 3p³(⁴S)(λ= 178.77 nm). Major experimental modification to the line attenuation technique in the vacuum ultraviolet following repetitive irradiation is described. This involves the use of “pre-trigger” pulsing and efficient electronic gating of a new, high gain photomultiplier tube, specifically designed for this purpose, by means of a de-focussing electrode. Absolute kinetic data for the reactions of P(3⁴S) are reported for the molecules PCl₃ and NO, yielding k_PCl3= 2.5 ± 0.05 × 10^–11 and k_NO= 4.3 ± 0.1 × 10^–13 cm³ molecule^–1 s^–1(300 K). These data are compared with analogous data for the optically metastable 3p³(²D_J) and 3p³(²P_J) states. Curve-of-growth calculations {ln[ln(I₀/I_tr)] against ln[P(3⁴S)]} are described for the λ= 177.50 nm transition which include the effect of magnetic dipole nuclear hyperfine interaction. Calculated and experimental curves are compared and discussed.