Kinetic study of Mg(33Pj) by time-resolved emission, 33P1→ 31S0+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(3PJ)], 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 3P0,1,2 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 3PJ) 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 τe= 2.1 ± 0.5 ms. The collisional quenching of Mg(3 3PJ) has also been investigated, yielding second-order absolute rate constants (kQ/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.