Color-center laser spectroscopy of transient species produced by excimer-laser flash photolysis

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Abstract
Kinetic spectroscopy based on excimer-laser flash photolysis and color-center-laser (CCL) infrared probing is explored. In simple absorption, the achievable signal-to-noise ratio (S/N) is not satisfactory even though the signal itself (corresponding to >1% absorption) is fairly large. This is due to amplitude fluctuations of the CCL. By using a double-beam detection scheme to balance out these amplitude fluctuations the sensitivity can be improved to the extent that a 1% absorption gives a S/N ˜ 100. In certain situations transient decreases in absorption of the precursor and transient increases in absorption due to final product formation can produce severe interfering signals even in simple systems. This problem is overcome without a major loss in sensitivity by a recently developed 45° magnetic rotation scheme. These points are illustrated with spectra of Br, OH, and NH2.