The time-resolved LMR method as used to measure elementary reaction rates of CI atoms and SiH 3 radicals in pulse photolysis of S 2Cl 2 in the presence of SiH 4

Abstract

The time-resolved laser magnetic resonance (LMR) method has been applied to kinetic measurements for the first time. An intracavity spectrometer based on a CO 2 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 SiH 3 radicals were obtained in the pulse photolysis of a mixture of S 2Cl 2 + SiH 4 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: [S 2Cl 2 = (2.0−10.2)×10 14 cm −3, [SiH 4 = (2.4−17.4)×10 13 cm −3. To remove the transition saturation, 5.3×10 15 cm −3 CCl 4 was introduced into the reactor. The fraction of dissociated S 2Cl 2 was 1‰ Rate constants of the reactions (I) Cl+S 2Cl 2 → products, (II) Cl+SiH 4 → HCl+SiH 3 and a preliminary rate constant of the reaction (III) SiH 3 + S 2Cl 2 → products were obtained: k 1 ≤ (4.3±1.2)×10 −12 cm 3/s, k 2 = (2.3±0.5)×10 −10 cm 3/s, k 3 = (2.4±0.5)×10 −11 cm 3/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 SiH 3 radicals was 4×10 10 cm −3 and = 10 11 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.