Cavity ring down absorption spectroscopy

Rom Romanzin, C., Boye-Peronne, S., Gauyacq, D., Benilan, Y., Gazeau, M.-C., Douin, S. CH radical production from 248 nm photolysis or discharge-jet dissociation of CHBrs probed by cavity ring-down absorption spectroscopy, J. Chem. Phys. 125 (2006) 114312, p. 1-9. 

A second independent method of direct absorption spectroscopy has been recently applied to clusters cavity ring down (CRD) spectroscopy. This method, where a sample is introduced into the cavity of a high finesse Fabry-Perot interferometer, and is shown schematically in Fig. 3. 

Cavity ring down (CRD) spectroscopy, having proven to be a very sensitive method for detecting molecular species in a wide variety of environments, has also been applied to the mid infrared vibrational spectroscopy of hydrogen-bonded clusters of water " and alcohols.As a direct absorption method, it can be used to quantitatively measure important molecular properties, such as absorption cross sections and coefficients. Knowing these properties, as a function of cluster size and structure, is useful in making the connection to the condensed phase. The sensitive detection of methanol clusters, as shown in Fig. 13, is of considerable importance. These particular measurements nicely complement the action spectra of methanol clusters, detected by depletion of mass-detected signal via vibrational predissociation. 

Zalicki P and Zare R N 1995 Cavity ring-down spectroscopy for quantitative absorption-measurements J. Chem. 

Fig. 1.47. Absorption spectrum of gold atoms deposited on an amorphous silica surface investigated by cavity ring-down spectroscopy...

Cavity Ring-Down Spectroscopy was introduced in 1988 by O Keefe and Deacon as a spectroscopic method for absorption measurements (O Keefe and Deacon, 1988). It is a versatile high sensitivity absorption technique. One of the most essential advantages of CRDS in contrast to usual absorption methods is that the CRDS signal is not affected by intensity fluctuations of the laser since only the decay time of the signal, which does not depend on the laser intensity, is detected. 

SiH2 is a highly reactive species which may undergo fast insertion reactions into o bonds and addition reactions to n bonds. The available work on the elementary reactions of SiH2 up to 1994 has been reviewed in detail by Jasinski et al. Because of its intense and well-resolved Bi <— Ai electronic absorption in the visible spectrum,SiH2 is easily detected with high sensitivity by laser-induced fluorescence, laser resonance absorption flash kinetic spectroscopy, or cavity ring-down spectroscopy. These techniques... 

How Howie, W.H., Lane, I.C., Newman, S.M., Johnson, D.A., Orr-Ewing, A.J. The UV absorption of CIO Part 1. The A 11 - X 11 spectrum at wavelengths from 285-320 nm studied by cavity ring-down Spectroscopy, Phys. Chem. Chem. Phys. 1 (1999) 3079-3085. 

All these techniques may be combined with intracavity absorption when the sample molecules are placed inside the laser resonator to enhance the sensitivity. Cavity ring-down spectroscopy yields absorption spectra with a detection sensitivity that is comparable to the most advanced modulation techniques in multipass absorption spectroscopy. 

Novel modalities with high sensitivity for general detection of analytes are scientifically invaluable and deserve more research efforts. Cavity ring-down spectroscopy for absorption... 

Tunable lasers (preferentially dye lasers and diode lasers) are used as primary sources for atomic absorption spectroscopy with various atomizers such as flames, furnaces, or plasmas LAAS laser atomic absorption spectrometry CRS cavity ring-down spectroscopy... 

Intraeavity Absorption and Cavity Ring-Down Spectroscopy... 

In contrast, absorption spectroscopy allows for more direct and more accurate, absolute concentration and temperature measurements. An increasingly popular approach for the detection of (minor) species in flames is cavity ring-down spectroscopy, CRDS. It combines the advantage of common absorption techniques, i.e. the direct determination of number density, with an effective absorption path of up to a few kilometres. Therefore, the detection of species of very low concentrations is possible. For a description of the principles of CRDS see Section 7.2. A typical experimental setup for the quantitative measurement of species concentration and temperature in flames is shown in Figure 29.7. 

The main part of the book presents various applications of lasers in spectroscopy and discusses the different methods that have been developed recently. Chapter 6 starts with Doppler-limited laser absorption spectroscopy with its various high-sensitivity detection techniques such as frequency modulation and intracavity spectroscopy, cavity ring-down techniques, excitation-fluorescence detection, ionization and optogalvanic spectroscopy, optoacoustic and optothermal spectroscopy, or laser-induced fluorescence. A comparison between the different techniques helps to critically judge their merits and limitations. 

During the last ten years a new, very sensitive detection technique for measuring small absorptions, cavity ring-down spectroscopy (CRDS), has been developed and gradually improved. It is based on measurements of the decay times of optical resonators filled with the absorbing species [6.31]. We can understand its general principle as follows ... 

Instead of Raman spectroscopy, infrared absorption spectroscopy can be used in cases of infrared-active transition, for example, for CO, CO2, NO, and CH4. With cavity ring-down spectroscopy a high sensitivity can be reached and spurious molecular concentrations resulting from fermentation processes in the stomach can still be detected [15.152]. 

New absorption methods, like intracavity spectroscopy, cavity-ring-down and cavity-enhanced spectroscopy, have demonstrated very high sensitivities in laboratory measurements with DLs. An ultrasensitive technique that combines external cavity enhancement and FM spectroscopy has been developed recently. This method, which has been called NICE-OHMS. or noise-immune cavity-enhanced optical heterodyne molecular spectroscopy, is based on frequency modulation of the laser at the cavity free-spectral-range frequency or its multiple. The MDA of 5x 10 1 X 10 cm ) in the detection of narrow... 

Brown, S.S., R.W. Wilson, and A.R. Ravishankara (2000), Absolute intensities for third and fourth overtone absorptions in HNO3 and H2O2 measured by cavity ring down spectroscopy, J. Phys. Chem. A, 104, 4976 983. 

D. Romanini, K.K. Lehmann, Ring-down cavity absorption spectroscopy of the very weak HCN overtone bands with six, seven and eight stretching quanta. J. Chem. Phys. 99, 6287 (1993)... 

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