Investigation of Time‐Resolved Molecular Chemiluminescence from SrO(A'1 Π, A1Σ+ ‐ X1Σ+) and Atomic Emission from Sr(53P1 ‐ 51S0) Following Pulsed Dye‐Laser Generation of Sr(53PJ) in the Presence of CO2

Abstract

AbstractWe present a kinetic study of chemiluminescence from SrO(A1Σ+ ‐ X1Σ+) and SrO(A'1 Π ‐ X1Σ+) following pulsed dye‐laser generation of Sr(5s5p(3PJ)), 1.807 eV above the 5s2(1S0) ground state, in the presence of CO2. This required complementary investigation of the time‐dependence of both the atomic emission profiles at the resonance wavelength of λ = 689.3 nm (Sr(5s5p(3P1)) Σ Sr(5s2(1S0)) + hv) and at wavelengths of various vibronic transitions within the A—X and A'— X band systems of SrO, together with the determination of the quantitative relationship between these using the appropriate time‐dependent equations for atomic and molecular emission. Decay profiles for Sr(53PJ) in the presence of CO2 across the temperature range T = 675—1100 K showed clear exponential decay behaviour, yielding the absolute second order rate constant for total collisional removal of the excited atoms of k1 = (4.7 ± 2.8) Σ 10−10 exp(‐ 33.3 ± 9.9 kJ mol−1 /RT) cm3 molecule −1 s−1. At elevated temperatures, the Arrhenius plot for the removal of Sr(53PJ) displayed upward curvature which is shown to be sensibly consistent with the removal of this atomic state by product SrO(X1Σ+). Chemiluminescence from transitions involving Δv sequences within SrO(A1Σ+ ‐ X1Σ+) and within the v = 0 progression of SrO(A'1Π ‐ X1Σ+) was monitored and analysed across the temperature range 900–1100 K. These molecular chemiluminescence profiles exhibited clear bi‐exponential behaviour which, when compared with the single exponential profiles for Sr(53PJ), were quantitatively shown to be consistent with the E—(E, V) transfer processes: Sr(53PJ) + SrO(X1Σ+) → SrO(A1Σ+, A'1Π, v' = n) + Sr(51S0). Vibrational excitation by this mechanism was observed up to the maximum energetically allowed by the relevant E ‐ (E, V) process. A ‐ X and A'‐ X chemiluminescence was shown to provide kinetic spectroscopic markers in the time‐domain for Sr(53PJ). Estimated vibrational temperatures within SrO(A'1II) indicated some measure of vibrational excitation accompanying energy transfer. The temperature variation of the SrO(A ‐ X) and SrO(A'‐X) emission intensity was demonstrated to be consistent with thermodynamic data for atomic strontium.