Kinetic study of Mg(3 3Pj) by time-resolved emission, 3 3P1→ 3 1S0+hν(λ= 457.1 nm), following dye-laser excitation

Abstract

A kinetic study of the low lying, optically metastable, electronically excited magnesium atom, Mg[3s3p(³P_J)], is presented. Mg(3 ³P₁) was generated by rapid, dye-laser pulse excitation at λ= 457.1 nm of magnesium vapour at 800 K in a slow-flow reactor, kinetically equivalent to a static system and monitored, following fast Boltzman equilibration of the close lying spin–orbit levels within the 3 ³P_0,1,2 manifold, by the subsequent “slow” spontaneous emission at the excitation wavelength, Mg(3 ³P₁)→ Mg(3 ¹S₀)+hν. (I) The experimental procedure included repetitive dye-laser pulsing, photoelectric detection with “pretrigger photomultiplier gating”, boxcar integration and kinetic analysis of the resulting XY-output. The diffusional decay of Mg(3 ³P_J) was studied in the presence of all the noble gases, He, Ne, Ar, Kr and Xe, together with detailed measurements of the mean radiative lifetime of transition (I)(at λ= 451.7 nm), which is reported as τ_e= 2.1 ± 0.5 ms. The collisional quenching of Mg(3 ³P_J) has also been investigated, yielding second-order absolute rate constants (k_Q/cm³ molecule^–1 s^–1, 800 K) for the following gases (errors 1σ): N₂, 4.9 ± 0.2 × 10^–13; H₂, 7.3 ± 0.6 × 10^–13; CO, 1.4 ± 0.1 × 10^–12; O₂, 3.3 ± 0.8 × 10^–11; CH₄, 1.1 ± 0.2 × 10^–14; Kr, ⩽ 2.3 × 10^–15; Xe, ⩽ 1.0 × 10^–15. The results are compared, where possible, with previous measurements derived primarily from investigations of time-resolved atomic resonance absorption spectroscopy following pulse dye-laser excitation and from intensity measurements of the forbidden emission 3 ³P₁→ 3 ¹S₀+hν in a flow–discharge system. The quenching rate constants are found to be in accord with the results of these earlier measurements.