Kinetic investigation of the molecular chemiluminescence SrBr(A2II, B2Σ+ → X2Σ+) and the time-resolved atomic fluorescence Sr(53P1 → 51S0) following the pulsed dye-laser generation of Sr(53PJ in the presence of CH3Br and CF3Br

Abstract

A kinetic study is presented of the vibronic energy distribution in SrBr following the reactions of the optically metastable, electronically excited strontium atom, Sr(5s5p(3PJ)), 1.807 eV above its 5s2(1S0 electronic ground state, in the presence of CH3Br and CF3Br. Sr(53P1) was generated by pulsed dye-laser excitation of ground-state strontium vapour at λ=689.3 nm (Sr(53P1←51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. The decay of Sr(53PJ) is then monitored by time-resolved atomic fluorescence from Sr(53P1) at the resonance wavelength following rapid Boltzmann equilibration within the 3PJ spin-orbit manifold using boxcar integration. Time-resolved molecular chemiluminescence to the ground state was also observed from electronically excited strontium bromide and investigated in detail via the SrBr(A2Πsol:32 → X2Σ+ (Δν=0, λ≈667 nm) and SrBr(B2Σ+ → X2Σ+) (Δν=0, λ≈651 nm) systems. The A2Π (177.6 kJ mol−1 and B2Σ+ (183.6 kJ mol−1) states of SrBr are both energetically accessible on collision between Sr(3P) and CH3Br and CF3Br. Both the atomic and molecular (A,B,–X) chemiluminescence emissions are shown to be exponential in form with both reactants and characterized by first-order decay coefficients which are found to be equal under identical conditions within experimental error. SrBr(A2Π) and SrBr(B2Σ+ are thus shown to arise from direct reaction with both CH3Br and CF3Br. The results obtained here in the time domain are compared with analogous chemiluminescence studies on Sr(3P) with halides, including bromides, using molecular beams and with previous time-resolved measurements on SrCl(A3II, B2Σ+ X2Σ+) that we have reported. The results are also compared with those from a series of investigations we have presented from time-domain investigations of molecular emissions from CaF, Cl, Br, I (A,B–X) arising from the collisions of Ca(43PJ) with appropriate halides.