Kinetic investigation of the collisional quenching of Mg(3 3PJ) by N2O over the temperature range 600–1100 K by time-resolved atomic emission and E–(E, V) transfer between Mg(3 3PJ)+ MgO by molecular chemiluminescence following pulsed dye-laser excitation at λ= 457.1 nm [Mg(3 3P1)â†� Mg(3 1S0)]

Abstract

We present a detailed kinetic investigation of the temperature dependence of the collisional removal of the electronically excited Group IIA element, Mg(3 ³P_J), 2.712 eV above its 3 ¹S₀ ground state with the simple oxidant molecule, nitrous oxide. The atomic ³P_J state was generated by the pulsed dye-laser excitation of Mg vapour at λ= 457.1 nm [Mg(3 ³P₁)â†� Mg(3 ¹S₀)] and monitored in the time-resolved mode by the forbidden emission at the resonance wavelength. The absolute second-order quenching rate constant for the removal of Mg(3 ³P_J) by nitrous oxide over the temperature range 600–1100 K is given by k_N2O=(2.6 ±^3.5_1.5)× 10^–10 exp (–41.3 ± 5.3 kJ mol^–1/RT) cm³ molecule^–1 s^–1. We also present a kinetic study of the time-resolved molecular emission in this system from magnesium oxide. Each molecular emission exhibited a maximum in the profiles, indicating their population not by direct reaction from Mg(3 ³P_J) with nitrous oxide, but by electronic energy transfer between Mg(3 ³P_J) and the long-lived states MgO(X¹Σ⁺, a³Π, A¹Π, b³Σ⁺) resulting from earlier reaction. This is analysed in terms of the atomic kinetics of Mg(3 ³P_J). The molecular emission may be employed as a spectroscopic marker for Mg(3 ³P_J) itself. Vibrational temperatures have been measured from progressions in the B–A system, indicating values in the range 2–5 times that of the ambient temperature and demonstrating E–(E, V) excitation on collision of Mg(3 ³P_J)+ MgO. Relative yields for the different vibronic states indicated that [MgO(d³Δ)] and [MgO(D¹Δ)]≈ 10^–3[MgO(B¹Σ⁺)]. Fundamental collision processes yielding electronic excitation to the emitting states of MgO are considered. The variation of the yields of a given electronic state of magnesium oxide following E–(E, V) transfer with temperature is consistent with thermodynamic data for magnesium vapour.