Determination of the Branching Ratios of CaBr(A²Π_1/2,3/2, B²Σ⁺) Resulting from the Reaction of Ca[4s4p (³P_J)] with CH₃Br by Time-Resolved Atomic Emission and Molecular Chemiluminescence Following Pulsed Dye-Laser Excitation of Atomic Calcium

Molecular electronic branching ratios to yield CaBr(A²Π_1/2), CaBr(A²Π_3/2) and CaBr(B²Σ⁺) have been determined in the time-domain following the reaction of Ca[4s4p (³P_J)], 1.888 eV above the 4s²(¹S₀) ground state, with CH₃Br. Ca[4s4p (³P₁)] was generated by the pulsed dye-laser excitation of ground state calcium atoms at λ=657.3 nm {Ca[4s4p (³P₁)]← Ca[4s²(¹ S ₀)]} at elevated temperatures in the presence of CH₃Br and excess helium buffer gas. Measurements were then made of the atomic resonance fluorescence from Ca(4³P₁→ 4¹ S ₀) and the molecular chemiluminescence from CaBr(A²Π_1/2, A²Π_3/2, B²Σ⁺→X²Σ⁺) after Boltzmann equilibration with Ca(4³P_0,1,2). The following molecular chemiluminescence emissions were recorded: CaBr(A²Π_1/2→ X²Σ⁺, Δ v =0, λ 628 nm), CaBr(A²Π_3/2→ X ²Σ⁺, Δ v =0, λ 625 nm) and CaBr(B²Σ⁺→ X²Σ⁺, Δ v =0, λ 611 nm). The atomic and molecular emissions demonstrated exponential decays characterised by decay coefficients which were equal under identical chemical conditions thus demonstrating the production of CaBr(A²Π_1/2,3/2, B²Σ⁺) by direct reaction of Ca(³ P _J ) with CH₃Br. The combination of the time-dependences of the atomic and molecular profiles together with the integrated atomic and molecular intensities, placed on a common intensity scale by calibration of the optical system against a spectral radiometer, yielded branching ratios into the A²Π_1/2, A²Π_3/2 and B²Σ⁺ states of CaBr. These were found to be as follows: A_1/2(9.8±3.0) · 10^-4; A_3/2 (8.5±3.4) · 10^-4 and B, (3.4±1.7) · 10^-4. To the best of our knowledge, these data represent the first measurements of electronic branching ratios of calcium bromide into specific molecular states for reactions of Ca(4³ P_J). The results are compared with various related data for total branching ratios into electronic states studied in the single collision condition for this atomic state with CH₃Br using molecular beams, and with analogous measurements for Ca(4³P_J) + CH₃F and CH₃Cl. These results are also compared with branching ratios of SrBr(A²Π_1/2, A²Π_3/2, B²Σ⁺) following the reaction of Sr[5 s 5 p (³P_J)]+ CH₂Br₂ investigated following pulsed dye-laser generation of Sr(5³P_J).