Laser-induced fluorescence, hydrogen

In order to relate material properties with plasma properties, several plasma diagnostic techniques are used. The main techniques for the characterization of silane-hydrogen deposition plasmas are optical spectroscopy, electrostatic probes, mass spectrometry, and ellipsometry [117, 286]. Optical emission spectroscopy (OES) is a noninvasive technique and has been developed for identification of Si, SiH, Si+, and species in the plasma. Active spectroscopy, such as laser induced fluorescence (LIF), also allows for the detection of radicals in the plasma. Mass spectrometry enables the study of ion and radical chemistry in the discharge, either ex situ or in situ. The Langmuir probe technique is simple and very suitable for measuring plasma characteristics in nonreactive plasmas. In case of silane plasma it can be used, but it is difficult. Ellipsometry is used to follow the deposition process in situ. 

The difference in H2 selectivity between Pt and Rh can be explained by the relative instability of the OH species on Rh surfaces. For the H2-O2-H2O reaction system on both and Rh, the elementary reaction steps have been identified and reaction rate parameters have been determined using laser induced fluorescence (LIF) to monitor the formation of OH radicals during hydrogen oxidation and water decomposition at high surface temperatures. These results have been fit to a model based on the mechanism (22). From these LIF experiments, it has been demonstrated that the formation of OH by reaction 10b is much less favorable on Rh than on Pt. This explains why Rh catalysts give significantly higher H2 selectivities than Pt catalysts in our methane oxidation experiments. 

In the following we present an application of laser induced fluorescence to a study of the chemistry of sulfur in rich hydrogen/oxygen/nitrogen (H2/O2/N2) flames and demonstrate a simple rationale for taking quench effects into account. Fluorescence measurements for S2, SH, S02, SO, and OH along with measurements of flame temperature and H-atom (in sulfur free flames) have been employed to develop a kinetic model for the highly coupled flame chemistry of sulfur. The kinetic aspects of the study already have been presented in considerable detail (6). 

In these experiments, we use multiphoton dissociation at 193 nm to generate C2 radicals. C2 concentrations are subsequently monitored using laser induced fluorescence. Disappearance rates of both Cj X3 g and a3IIu are reported at ambient temperature with hydrocarbons (CH , C2H2, CjH, and C2H6), hydrogen, oxygen, and carbon dioxide. 

Hydrogen. The reaction of O ( D2) with H2 takes place on the ground state potential surface of water, HiOf Ai). On the basis of trajectory calculations, (Whitlock et al., 1982) it has been suggested that, as is true for the hydrocarbons, parallel mechanisms involving insertion/elimination and direct abstraction govern the course of this reaction. The observation using laser induced fluorescence spectroscopy (Luntz et al., 1979 Smith and Butler, 1980) of a highly excited, non-Boltzmann rotational distribution and a nearly statistical vibrational distribution for v" = 1 and v" = 0 is consistent with the insertion/elimination... 

Commentary on Crossed-Beam Reactions of Barium with Hydrogen Halides Measurement of Internal State Distributions by Laser-induced Fluorescence, H. W. 

The use of laser-induced fluorescence as a molecular beam detector for the measurement of internal state distributions of reaction products is presented and applied to the reactions of barium with the hydrogen halides. It is found that most of the reaction exoergicity appears as translational energy of the products and that the total reactive cross section is positively correlated with the average fraction of the exoergicity appearing as vibrational excitation. 

In this paper we describe the use of laser-induced fluorescence as a molecular beam detector and apply it to the reactions of barium atoms with hydrogen halides,... 

E. Fridell, U. Westblom, M. Alden, and A. Rosen, Spatially resolved laser-induced fluorescence imaging of OH produced in the oxidation of hydrogen on platinum, J. CataL 725 92 (1991). 

Fridell, E., Elg, A.P., Rosen, A., Kasemo, B. A laser-induced fluorescence study of OH desorption from Pt(lll) during oxidation of hydrogen in 0-2 and decomposition of water. J. Chem. Phys. 1995,102, 5827-35. 

In nonhydrogen bonding solvents, this molecule was shown to emit only at 500 nm. Emission at 390 nm could only be obtained in alcohols. These results demonstrate that the ultraviolet fluorescence component is due to molecules in which the carbonyl oxygen is not hydrogen bonded to the hydroxyl group. Equilibrium cannot be established between the two tautomers in the excited state only molecules which are in the correct ground state configuration will participate in a proton translocation. This proton translocation takes place in under 10 ps. Since neither a temperature dependence nor an isotope effect could be observed, the dynamic measurements do not elucidate the mechanism for the proton translocation. This question has been answered in part by the appUcation of laser-induced fluorescence. 

A brief report has appeared on the crossed-beam reaction between Ba and LiCl, using laser-induced fluorescence detection of the BaCl product, which gives a lower bound for the bond-dissociation energy of BaCl of 110 3 kcal mol-1.242 Similar studies on the reactions of alkali-metal dimers with hydrogen atoms and molecules 243 and the photodissociation of alkali-metal iodides244 have been reported. 

S. Agrup, F. Ossler, M. Alden Measurement of collisional quenching of hydrogen atoms in an atmospheric pressure hydrogen/oxygen flame by picosecond laser-induced fluorescence. Appl. Phys. B 61, 479 (1995)... 

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