Infrared Absorption Measurements
Multipass optics and frequency-modulation techniques are used by Craig Taatjes to provide improved detection sensitivity in the Laser Chemistry Laboratory. With these sensitivity enhancements, we can precisely measure rate coefficients and product branching fractions. Our multipass cell was specifically designed for use in temperature-dependent laser pump-probe measurements of chemical kinetics and combines long pathlengths with precise temperature control. The use of two-tone frequency modulation can further increase the sensitivity of detection in the infrared. One example of how improved sensitivity can be put to use is our measurements of the absolute rate coefficients of the reactions of chlorine atoms with allene and propyne. Both reactions can form propargyl radical, thought to be an important intermediate in the formation of soot. Although both reactions might be thought to proceed similarly, the kinetics of the two reactions are markedly different. Most recently, the infrared absorption technique has been applied to investigations of HO 2 and OH formation in the reactions of alkyl radicals with O 2.
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