Diode laser spectroscopy

Mohebati A., King TA., Remote detection of gases by diode laser spectroscopy, J. Modem Optics 1988 35 (3) 319-324. 

Infrared diode laser spectroscopy has been used for the measurement of hydrocarbon and CO concentrations in exhaust (13, 14, 15). The adsorption path length, and thus the absorption cell volume, required for hydrocarbon measurement is rather large, limiting the time-resolution of the measurement. The absorption path length required for CO measurement, however, is relatively short and approximately equal to the diameter of a standard exhaust pipe. This allows CO to be measured with high time-resolution by an infrared laser beam passed through an... 

Sell, J. A. Herz, R. K. Monroe, D. R. "Dynamic Measurement of Carbon Monoxide Concentrations in Automotive Exhaust Using Infrared Diode Laser Spectroscopy" SAE Paper No. 800463, 1980. 

Infrared diode laser spectroscopy, 46 119, 148 Infrared emission, transition,-metal ions, 35 334-335... 

Other infrared absorption techniques are also used in ambient air measurements, including tunable diode laser spectroscopy (TDLS), nondispersive infrared (NDIR) spectroscopy, and matrix isolation spectroscopy. These are discussed in more detail later. 

FIGURE 11.31 Comparison of gaseous HN03 measurements made simultaneously in Claremont, California, on two different days using FT-IR shown as with error bars and by a filter pack (FP), a difference denuder (DD), an annular denuder (AD), and tunable diode laser spectroscopy (TDLS) (adapted from Hering et al., 1988). 

Later chapters detail application of the present method to electron spectroscopy for chemical analysis (Chapter 5), high-resolution dispersive infrared spectroscopy (Chapter 6), and tunable-diode-laser spectroscopy (Chapter 7). Because the heart of the method is the repeated application of simple convolution, the method has been adapted to the processing of images (Kawata et al, 1978 Kawata and Ichioka, 1980a Saghri and Tescher, 1980 Maitre, 1981 Gindi, 1981). 

Airborne tunable laser absorption spectrometer infrared absorption by tunable diode laser spectroscopy 41... 

Wall-coated flow tube reactors have been used to study the uptake coefficients onto liquid and solid surfaces. This method is sensitive over a wide range of y (10" to 10 1). For liquids this method has the advantage that the liquid surface is constantly renewed, however if the uptake rate is fast, the liquid phase becomes saturated with the species and the process is limited by diffusion within the liquid, so that corrections must be applied [70,72,74]. Many experiments were designed to investigate the interaction of atmospheric species on solid surfaces. In this case the walls of the flow tube were cooled and thin films of substrate material were frozen on the wall. Most of the reaction probabilities were obtained from studies on flow tubes coated with water-ice, NAT or frozen sulfate. Droplet train flow tube reactors have used where liquid droplets are generated by means of a vibrating orifice [75]. The uptake of gaseous species in contact with these droplets has been measured by tunable diode laser spectroscopy [41]. 

In reactions 16a-f, OM and OM designate organometallic or hydrocarbon species or fragments. The presence of CH3- radicals has been verified by infrared (IR) diode laser spectroscopy (116), and the reaction mechanisms have been investigated by replacing the usual H2 ambient by D2 (118-120). Reactions 16a-f form a typical free-radical mechanism with initiation (16a and b), chain-transfer (16c), propagation (16d), and termination (16e and f) reactions. 

P. B. Davies and D. M. Smith,/. Chem. Phys., 100, 6166 (1994). Diode Laser Spectroscopy and Coupled Analysis of the v2 and v4 Fundamental Bands of SiH3. 

C. Yamada and E. Hirota, Phys. Rev. Lett., 56, 923 (1986). Detection of the Silyl Radical SiH3 by Infrared Diode-Laser Spectroscopy. 

From the above considerations, it follows that C02-HI will most probably be inertially T-shaped, with at least as large a hydrogen zero point amplitude as for the case of C02-HBr. There is no fundamental reason why the structure of this complex has not yet been measured. We attempted this once by using high resolution infrared tunable diode laser spectroscopy and confirmed the inertially T-shaped character (Lin et al. n.d). However, before accurate rotational constants could be obtained, the HI ruined the vacuum pump, as it is prone to do. This lessened our appetite for a more precise structural determination. 

Experiments are currently in progress to measure CO and NO concentrations in a flat flame burner by diode laser spectroscopy. Comparative measurements are also being made using microprobe sampling with subsequent analysis by non-dispersive infrared and chemiluminescent techniques. Some preliminary laser absorption results for CO are reported here initial results for NO have been published separately (4). Also reported are initial data for collision halfwidths in combustion gases. 

CIRDLS = infrared diode laser spectroscopy ES = electronic spectroscopy, spectra with resolved vibrational structure MW = microwave spectroscopy force field calculations denote harmonic frequencies obtained on the basis of combined analysis of electron diffraction and vibrational spectroscopy data. 

Infra-red chemiluminescence has been used to measure the vibrational state distributions of CO2 formed by reaction on Pt and Pd surfaces [45-50]. While the detection sensitivity of infrared chemiluminescence does not approach that of LIF or REMPI, it is an attractive way to probe molecules such as CO2 where there is substantial vibrational excitation and REMPI schemes are not available. In some cases Doppler measurement of the translational energy release can be achieved, giving direct information on the translational energy release of vibrationally excited C02 [45]. Recently infrared diode laser spectroscopy has been used to detect vibrationally excited CO2 from CO oxidation over... 

Thermal reaction mixtures in this work were analyzed by FTIR spectroscopy, tunable diode laser spectroscopy and vibrational circular dichroismA pair of representative VCD spectra are shown in Figure 1. The more intense spectrum is an optically pure reference sample of the (25, 35) isomer at 53.59 torr the other is a thermal reaction product mixture from this isomer after 360 min at 407 °C and gas chromatographic isolation, recorded at 81.30 torr . From the measured Ay4/A 4ref absorption intensity ratio and the pressures, one may calculate that the sample retains 51.65% of its original optical activity, which compares well with the value calculated from the value obtained from the least-squares fit of all five VCD experimental points (51.2%). These spectra, obtained in the gas phase with a few mg of chromatographically purified labeled cyclopropanes, demonstrate the promise of VCD for assessing enantiomeric excess in situations where classical polari-metric methods would be of limited utility. 

Spectra of the linear anion FHF in the gas phase were obtained by diode laser spectroscopy P = 583.6539(13) cm, uj = 1286.0284(22) cm , and 1 3 = 1331.1502(7) cm . From the resulting rotational constants an equilibrium F-F intemuclear distance of 227.771(7) pm was calculated (Kawaguchi and Hirota, 1987). In the class of binary hydrides, boron compounds are especially interesting. A recent FTIR investigation revealed the out-of-plane vibration of unstable BH3 1140.8757(39) cm (Kawaguchi et al., 1987). These data confirm the results of a recent matrix study which showed an absorption at 1132 cnr for the same vibration (Kaldor and Porter, 1971). A detailed... 

A corresponding F2/CH3OH/O2 system has been used in discharge flow studies or alternatively the F2/H2O2 system. Detection methods include absorption [88], and i.r. diode laser spectroscopy [89] for time resolved studies and laser magnetic resonance for flow systems [90]. 

In our work on CO2-HX structures, tunable infrared diode laser spectroscopy was used to obtain geometries for X = F, Cl, and Br, using the CO2 asymmetric stretch chromophore [34], Both CO2-HF and CO2-HCI displayed the clear signatures of the linear equilibrium geometries that had been established previously [35, 36]. On the other hand, the C02-HBr spectrum showed that this complex is very asymmetric, which came as a surprise. We had originally assumed that C02-HBr was linear, by analogy with CO2-HF and COj-HCl. However, it is not. The observed C02-HBr spectra indicate a broadside inertial structure, with an u-axis moment of inertia close to that of uncomplexed CO2. Figures 11 and 12 show representative spectra that... 

Relative CO2-HCI and C02-HBr concentrations were measured under conditions similar to those used in the photoinitiated reactions, but in a completely separate apparatus that used pulsed slit nozzle expansions and tunable infrared diode laser spectroscopy. This was achieved by recording fully rotationally resolved CO2-HXIR absorption spectra using the CO2 asymmetric stretch chromophore, as described in Section III.A. The rotational distributions fit temperatures quite well, usually 3K. Rotational partition functions were calculated for the measured rotational temperatures and the areas under the absorption lines recorded for all transitions. From this, relative concentrations were determined. Details are available elsewhere [139, 140]. 

Valuable information on the kinetics and mechanism of CF3 + N02 comes from the experimental and theoretical study by Pagsberg et al,226 The experiments, performed using time-resolved infrared diode laser spectroscopy, were supported by ab initio calculations to provide insight into the potential energy surface of the reaction system. The reaction was initiated by pulse radiolysis of Ar/SF6/CF3I mixtures. The abstraction reaction of the iodine atom from CF3I by fluorine atoms leads to the formation of CF3 radicals. The reactions... 

Raman spectroscopy was used to probe high-pressure phase transitions for CF4 hydrate systems.366 High-resolution tunable diode laser spectroscopy for CF3C1 showed that the band origin for v, was at 1108.35587(6) cm-1 (35C1) or... 

Niemax K., Groll H. and Schnurer-Patschan C. (1993) Element analysis by diode laser spectroscopy, Spectro-chim Acta Rev 15 349-377. 

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