Determination of Branching Ratios in a Kinetic Investigation of the Atomic Resonance Fluorescence and Molecular Chemiluminescence, CaCl(A2Π1/2,3/2

Measurements in the time-domain of molecular chemiluminescence from CaCl ( A 2 Π 1 / 2,   A 2 Π 2 / 3,   B 2 Σ +   → X 2 Σ + ) and atomic resonance fluorescence from Ca ( 4 3 P 1 →   4 1 S 0 ) havebeen made in order to determine electronic branching ratios to yield CaCl ( A 1 / 2,   A 2 / 3,   B ) following the Cl-atom abstraction reaction of electronically excited calcium atoms,Ca [ 4 s 4 p (3 P J ) ] , 1.888 eV above the 4 s 2 (1 S 0 ) ground state, with CH 3 Cl. Ca [ 4 s 4 p (3 P 1 ) ] wasgenerated by the pulsed dye-laser excitation ofground state calcium atoms at λ = 657.3 nm21, { Ca [ 4 s 4 p ( n 3 P 1 ) ]   ← Ca [ 4 s 2 (1 S 0 ) ] } at elevated temigeratures in the presence of CH3Cl andexcess helium buffer gas in a slow flow system, kinetically equivalent to a static system.Atomic and molecular emissions were recorded following rapid Boltzmann equilibrationwithin the Ca ( 4 3 P 0 , 1.2) spin-orbit manifold, atomic emission being restricted tothe3 P 1state as the3 P 0and3 P 2states are long-lived, being so called ‘reservoir states’. Atomic fluorescence emission profiles at the resonance wavelength together with the molecular chemiluminescence emissions CaCl ( A 2 Π 1 / 2→ X 2 Σ + ,   Δ ν = 0 ,   λ = 621 nm ) ,CaCl A 2 Π 3 / 2→ X 2 Σ + ,   Δ ν = 0 ,   λ = 618 nm and CaCl ( B 2 Σ + → X 2 Σ + ,   Δ ν = 0 ,     λ = 593 nm ) were recorded. The atomic and molecular emissions demonstrated exponentialdecays characterised by decay coefficients which were equal under identical chemicalconditions thus demonstrating the production of CaCl ( A 2 Π 1 / 2 , 3 / 2,   B 2 Σ + ) by directreaction of Ca (3 p J ) with CH 3 Cl. The combination of the time-dependences of the atomic and molecular profiles as a function of the concentration of CH 3 Cl 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 theA 2 Π 1 / 2,A 2 Π 3 / 2andB 2 Σ +states of CaCl. These were found to be as follows: A1/ ( 2.6 ± 1.1 ) 2 × 10 − 3 ; A 2 / 3( 1.9 ± 0.8 ) × 10 − 3and B ( 3.6 ± 2.0 ) × 10 − 4 . To the best of ourknowledge, these data represent the first measurements of electronic branching ratios ofcalcium chlorides into specific molecular states for reactions of Ca (3 p J ) determined in the time-domain. The results are compared with various related data for total branching ratios into electronic states studied in the single collision condition for this atomic statewith CH3Cl using molecular beams. These are also compared with branching ratios ofSrCl ( A 2 Π 1 / 2,   A 2 Π 2 / 3,   B 2 Σ + ) following the reaction of Sr [ 5 s 5 p (3 p J ) ] + CH 2 Cl 2 investigated following pulsed dye-laser excitation where the yields of SrCl ( A 1 / 2,   A 3 / 2,   B ) were of similar low magnitudes.