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

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 450 magnetic rotation scheme. These points are illustrated with spectra of Br, OH, and NH 2 .

Time-Resolved Quantitative Measurement of OH HO2 and CH2O in Fuel Oxidation Reactions by High Resolution IR Absorption Spectroscopy.

“…mechanisms. In the laser chemistry lab at Combustion Research Facility at Sandia, we use laser flash photolysis [5,6], slow flow reactor to study low-temperature (< 800K) and low-pressure (< 100Torr) fuel oxidation chemistry [7]. High-resolution IR spectroscopic tools have been used to probe the time behavior of important intermediates and products in fuel oxidation reactions in situ.…”

Time-Resolved Laser-Flash Photolysis Faraday Rotation Spectrometer: A New Tool for Total OH Reactivity Measurement and Free Radical Kinetics Research

“…[19][20][21] FRS is based on the magneto-optic effect of paramagnetic species, which provides a powerful tool for gas phase chemical kinetic studies with high precision, high selectivity, and free of interferences from precursor's absorption. [22][23][24][25] Further improvements can make the system more compact, portable, and affordable, which provides a reliable approach for long-term and network k' OH observations.…”

“…In this work, we report the development of a new instrument that combines laser-flash photolysis with mid-infrared Faraday rotation spectroscopy (LFP-FRS) for real-time in situ measurement of k OH ′ and free radical kinetics studies. The OH decay was directly measured using a time-resolved FRS spectrometer at 2.8 μm. − FRS is based on the magneto-optic effect of paramagnetic species, which provides a powerful tool for gas phase chemical kinetic studies with high precision, high selectivity, and free of interferences from the precursor’s absorption. − Further improvements can make the system more compact, portable, and affordable, which provides a reliable approach for long-term and network k OH ′ observations.…”