Measurements of branching ratios of CaF(A(2)Pi(1/2,1/3)) from the reactions of Ca[4s4p(P-3(J))] with CH3F following pulsed dye-laser excitation of atomic calcium

Molecular electronic branching ratios to yield CaF(A(2)Pi(1/2)) and CaF(A(2 )Pi(3/2)) have been measured in the time-domain following the F-atom abstra ction reaction of electronically excited calcium atoms, Ca[4s4p(P-3(J))], 1 .888 eV above the 4s(2) (S-1(0)) ground state, with CH3F . Ca[4s4p P-3(1))] was generated by the pulsed dye-laser excitation of ground state calcium a toms at lambda = 657.3 nm (Ca[4s4p(P-3(1))] <-- Ca[4s(2) (S-1(0))]) at elev ated temperatures in the presence of CH3F and excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. Atomic fluore scence emission profiles at the resonance wavelength together with molecula r chemiluminescence emissions at lambda=606 nm, CaF(A(2)Pi(1/2) --> X(2)Sig ma(+), Delta v = 0) and lambda = 603 nm, CaF(A(2)Pi(3/2) --> X(2)Sigma(+), by = O) were recorded. These demonstrated exponential decays characterised by decay coefficients which were equal under identical chemical conditions thus demonstrating the production of CaF(A(2) Pi(1/2,3/2)) by direct reacti on of Ca(P-3(J)) with CH3E The combination of the time-dependences of the a tomic and molecular profiles as a function of the concentration of CH3F tog ether with integrated atomic and molecular intensities yielded branching ra tios into the A(2)Pi(1/2) and A(2)Pi(3/2) states which were found to be as follows: A(1/2), (1.4+/-0.6) x 10(-3); A(3/2), (1.2+/-0.5) x 10(-3). Whilst the higher lying CaF(B(2)Sigma(+)) is also energetically accessible on rea ction, the B-X chemiluminescence was not observed and is attributed to a lo w branching ratio on reaction into that state. The results are compared wit h various related data for Ca(P-3(J)) for total branching ratios into elect ronic states studied in the single collision condition and with branching r atios of SrF(A(2)Pi(1/2), A(2)Pi(3/2), B(2)Sigma(+)) following the reaction of Sr[5s5p(P-3(J))]+CH3F investigated following pulsed dye-laser excitatio n where the yields of SrF(A(1/2). A(3/2)) were of similar low magnitudes. ( C) 2000 Elsevier Science S.A. All rights reserved.