KINETIC INVESTIGATION OF THE TIME-RESOLVED ATOMIC FLUORESCENCE SR(5 P-3(1)-]5 S-1(0)) AND MOLECULAR CHEMILUMINESCENCE SRCL(A (2)PI, B (2)SIGMA-]X (3)SIGMA+ FOLLOWING THE PULSED DYE-LASER GENERATION OF SR(5 P-3(J)) IN THE PRESENCE OF CH3CL AND CF3CL()

A kinetic study of the vibronic energy distribution in SrCl following the collision of the optically metastable, electronically excited stro ntium atom, Sr[(5s)1(5p)1, 3P(J)], 1.807 eV above its (5s)2, 1S(o) ele ctronic ground state, in the presence of CH3Cl and CF3Cl is presented. This is investigated in the time-resolved mode following the generati on of the excited atom by pulsed dye-laser excitation at elevated temp erature from ground-state strontium vapour in the presence of reactant s and an excess of helium buffer gas in a slow-flow system, kineticall y equivalent to a static system. The decay of Sr(5 3P(J)) is monitored by time-resolved atomic fluorescence at the resonance wavelength [lam bda = 689.3 nm, Sr(5 P-3(1)) --> Sr(5 1S(o)) + h(nu)], following rapid Boltzmann equilibrium within the 5 3P(J) spin-orbit manifold using bo xcar integration. Electronically excited SrCl in the A 2PI1/2,3/2 and B 2SIGMA+ states, respectively 1.855 eV (179.0 kJ mol-1) and 1.948 eV (188.0 kJ mol-1) above the X 2SIGMA+ ground state, was also monitored by time-resolved molecular chemiluminescence of the A, B-X systems und er identical conditions to those employed for characterising the decay profiles of Sr(5 3P(J)). Both atomic and molecular chemiluminescence emissions showed exponential decay profiles, characterised by first-or der decay coefficients which were found to be equal under the same exp erimental conditions within experimental error. SrCl(A 2PI) and SrCl(B 2SIGMA+) are thus shown to arise from direct production on the collis ion of Sr(5 3p(J)) with CH3Cl and CF3Cl where these processes are ener getically favourable. These results from measurements in the time-doma in are considered with analogous data for Ca(4 3P(J)) Collisions invol ving F, Cl, Br and I atom abstraction reactions and with chemiluminesc ence from SrCl(A, B-X) systems in the single-collision condition follo wing the reaction of Sr(5 3p(J)) with various Cl-containing molecules.