The time-resolved LMR method as used to measure elementary reaction rates of CI atoms and SiH₃ radicals in pulse photolysis of S₂Cl₂ in the presence of SiH₄

The time-resolved laser magnetic resonance (LMR) method has been applied to kinetic measurements for the first time. An intracavity spectrometer based on a CO₂ laser with resonant modulation of the magnetic field and with phase-sensitive detection of the signal has been used. Kinetic curves of generation and disappearance of CI atoms and SiH₃ radicals were obtained in the pulse photolysis of a mixture of S₂Cl₂ + SiH₄ under the fourth harmonic of a Nd laser (265 nm, 0.5 mJ, 12.5 Hz) at a total pressure of 520-980 Pa (he as diluent) and a temperature of 326 K. The reagent concentrations were: [S₂Cl₂ = (2.0-10.2)×10¹⁴ cm^-3, [SiH₄ = (2.4-17.4)×10¹³ cm^-3. To remove the transition saturation, 5.3×10¹⁵ cm^-3 CCl₄ was introduced into the reactor. The fraction of dissociated S₂Cl₂ was 1‰ Rate constants of the reactions (I) Cl+S₂Cl₂ → products, (II) Cl+SiH₄ → HCl+SiH₃ and a preliminary rate constant of the reaction (III) SiH₃ + S₂Cl₂ → products were obtained: k₁ ≤ (4.3±1.2)×10^-12 cm³/s, k₂ = (2.3±0.5)×10^-10 cm³/s, k₃ = (2.4±0.5)×10^-11 cm³/s. At a signal-to-noise ratio of 1:1, 1000 pulses and a 12 cm long detection zone the sensitivity to Cl atoms and to SiH₃ radicals was 4×10¹⁰ cm^-3 and = 10¹¹ cm^-3, respectively. The time resolution of the method was 4 μs. The method is shown to be promising for kinetic investigations and experiments on fast processes.