Picosecond and nanosecond laser flash photolysis study of some halogenated benzene derivatives

Abstract

Picosecond laser photolyses of benzyl chloride, benzyl bromide and benzyl iodide vapour have been examined by monitoring the time profiles of fluorescence and absorption of benzyl radicals formed in the 266 nm photolysis. The decays of fluorescence for these molecules were well represented by two exponential functions. The short-lifetime component has a value of ca. 1 ns, and the longer one 5–9 ns. The time-resolved absorption of benzyl radicals obtained in the photolysis of benzyl chloride (0.5 Torr) showed that the rise time of benzyl radical absorption, 6 ns, could be attributed to the decomposition rate of benzyl chloride molecules under collision-free conditions, while the rise time for benzyl radicals formed in the photolyses of benzyl bromide and benzyl iodide was ca. 1 ns. Thus the photodecomposition rate of benzyl chloride is in good correlation to the value of the slow component and those of benzyl bromide and benzyl iodide to values of short components.