Electronic Energy Distribution in SrF by Investigation of the Molecular Chemiluminescence SrF(A2II1/2,3,2B2Σ+ → X2Σ+) and the Atomic Resonance Fluorescence Sr(53P1‐51S0) in the Time‐Domain following the Pulsed Dye Laser Generation of Sr(53PJ) in the presence of CH3F

Abstract

AbstractA kinetic study is presented of the electronic energy distribution in SrF following the reaction of the electronically excited strontium atom, Sr(5s5p(3Pj)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH3F. This optically metastable atom was generated by pulsed dye‐laser excitation of ground state strontium vapour to the Sr(53P1) state 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) was then monitored by time‐resolved atomic fluorescence from Sr(53P1) at the resonance wavelength following rapid Boltzmann equilibration within the 3PJ spin‐orbit manifold. Electronically excited SrF resulting from reaction of the excited atom with CH3F was also recorded in the time‐domain via the systems SrF(A2→1/2ΣX2Σ+) (νv = 0, λ = 662 nm), SrF(A2×3/2ΔX2Σ+) (ν = 0, λ = 652 nm) and SrF(B2Σ+X2Σ+) (νv = 0, λ = 579 nm). The A2 (181.9 kJ mol−1) and B2Σ+ (206.6 kJ mol−1) states of SrF are both energetically accessible on collision between Sr(3P) and CH3F. Both the atomic and molecular (A,B‐X) chemiluminescence emissions are shown to be exponential in form and characterised by first‐order decay coefficients which are found to be equal under identical conditions within experimental error. SrF(A2) and SrF(B2Σ+) are thus both shown to arise from direct reaction with CH3F. Further, the combination of integrated atomic and molecular intensity measurements, coupled with optical sensitivity calibration, enables estimates of the branching ratios into the A1/2,3/2, B and X states arising from Sr(53PJ) + CH3F to be made yielding the following results: A1/2, 6.4 × 10−3; A3/2, 1.5×10−3; B, 1.1x10−4; X, 0.992. The results obtained here are compared with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements and with previous kinetic measurements on SrCl, Br(A2, B2 + ‐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.