Kinetic investigation of the time-resolved atomic fluorescence Sr(53P1→ 51S0) and molecular chemiluminescence SrCl(A2Π, B2Σ+→ X3Σ+following the pulsed dye-laser generation of Sr(53PJ) in the presence of CH3Cl and CF3Cl

Abstract

A kinetic study of the vibronic energy distribution in SrCl following the collision of the optically metastable, electronically excited strontium atom, Sr[(5s)1(5p)1, 3PJ], 1.807 eV above its (5s)2, 1S0 electronic ground state, in the presence of CH3Cl and CF3Cl is presented. This is investigated in the time-resolved mode following the generation of the excited atom by pulsed dye-laser excitation at elevated temperature from ground-state strontium vapour in the presence of reactants and an excess of helium buffer gas in a slow-flow system, kinetically equivalent to a static system. The decay of Sr(5 3PJ) is monitored by time-resolved atomic fluorescence at the resonance wavelength [λ= 689.3 nm, Sr(5 3P1)→ Sr(5 1S0)+hν], following rapid Boltzmann equilibrium within the 5 3PJ spin–orbit manifold using boxcar integration. Electronically excited SrCl in the A 2Π1/2, 3/2 and B 2Σ+ states, respectively 1.855 eV (179.0 kJ mol–1) and 1.948 eV (188.0 kJ mol–1) above the X 2Σ+ ground state, was also monitored by time-resolved molecular chemiluminescence of the A, B–X systems under identical conditions to those employed for characterising the decay profiles of Sr(5 3PJ). Both atomic and molecular chemiluminescence emissions showed exponential decay profiles, characterised by first-order decay coefficients which were found to be equal under the same experimental conditions within experimental error. SrCl(A 2Π) and SrCl(B 2Σ+) are thus shown to arise from direct production on the collision of Sr(5 3PJ) with CH3Cl and CF3Cl where these processes are energetically favourable. These results from measurements in the time-domain are considered with analogous data for Ca(4 3PJ) collisions involving F, Cl, Br and I atom abstraction reactions and with chemiluminescence from SrCl(A, B–X) systems in the single-collision condition following the reaction of Sr(5 3PJ) with various Cl-containing molecules.