Laser-induced oxidation

Grabner, G. Li, G. Quint, R. M. Quint, R. Getoff, N. Pulsed laser-induced oxidation of phenol in acid aqueous TiOz sols, J. Chem. Soc., Faraday Trans. 1991, 87, 1097. 

Gevaert, M. Kamat, P. V. Visible laser-induced oxidation of C70 on titanium dioxide particles, J. Chem. Soc., Chem. Commun. 1992, 1470. 

The formation of odd oxygen species under pressurized conditions is possible even in the wavelength region that is somewhat longer than the dissociation threshold at 242.4 nm this is important as the initial reaction in the laser-induced oxidation of hydrocarbons in the hydrocarbon/02/supercritical C02 mixtures at 248 nm [5],... 

In the opposite case, hv > g, photons produce electron-hole pairs. Accumulation of holes at the oxide surface increases the local potential drop which may cause a fast photocorrosion. Ion migration is enhanced in the thin film, corrosion is enhanced, and altogether a fast dissolution of metal takes place by a photoelectro-chemical process in the passive film. An example is given for Ti [160]. This technique can be used for microstructuring of Ti- or Al surfaces [104]. On the other hand, anodic metal ion dissolution competes with the opposite anodic film forming ITR of oxygen ions. Therefore, in dependence on the special conditions, laser induced oxide growth may overcome pit formation [160]. 

The results from two-pulse correlation measurements for the laser-induced oxidation producing CO2 and CO desorption are shown in Figure 27.27 (top and bottom traces respectively). Notice how the time-scales for the two competing processes show almost an order of magnitude of difference. Whereas the ultrafast oxidation process yielding CO2 exhibits an FWHM of 3 ps, the CO desorption signal displays a much slower response with an FWHM of 20 ps. Clearly, the reaction O + CO CO2 seems to be driven by the hot electrons, whereas the CO desorption involves coupling to phonons. 

Figure 27.27 Two pulse correlation measurements for the laser-induced oxidation, producing CO2 (bottom trace) and CO desorption (top trace). Reproduced from Bonn et al. Science, 1999, 285 1042, with permission of AAAS...

A stereoselective determination of enantiomers of 5, its A -oxide and N-desmethyl metabolites in human urine was developed by capillary electrophoresis using laser-induced fluorescence detection and sulfonated /1-cyclodextrin in the running buffer (01JC(B)169). 

Methods for disposing of diisopropyl methylphosphonate include microwave decomposition, ultraviolet and infrared laser-induced photodestruction, chemical oxidation coupled with ultraviolet radiation catalyzation, and adsorption using granular activated carbon (Bailin et al. 1975 Calgon 1977 ... 

Two-dimensional distributions of ground-state NO were detected by planar laser-induced fluorescence during the process of NO removal in a corona radical shower system in NO/dry air mixtures [57,58], The authors observed that the density of NO molecules decreased not only in the plasma region formed by the corona streamers and the downstream region of the reactor, but also in the upstream region of the reactor. They explained this behaviour by oxidation with ozone, which is transported upstream by electrohydrodynamic flow. 

Several characteristics of the metal beam have been studied in detail. It is well known that metal clusters and metal oxides are formed as a result of the ablation process. However, these potentially interfering species have been studied in detail130 and it has been concluded that they do not introduce any doubt as to the validity of the experimental results. Much more important than cluster or oxide formation are the atomic electronic state populations of the metal beams. For each metal reactant, these have been characterized using laser-induced fluorescence (LIF) excitation spectroscopy. For Y, only the two spin-orbit states of the ground electronic state (a Dz/2 and a D-3,/2) were observed.123... 

Xiao H, Yang LS, Zou HF, Yang L, Le XC (2007) Analysis of oxidized multi-walled carbon nanotubes in single K562 cells by capillary electrophoresis with laser-induced fluorescence. Anal Bioanal Chem 387 119-126. 

Budde et have recently observed the ultraviolet laser-induced desorption of NO from oxidized Ni(lOO). The 193 nm excitation wavelength used was resonant with gas phase NO transitions to a predissociative upper state. Desorption yields of NO from clean Ni(lOO) were essentially zero. Comparison of TPD results from clean and oxidized nickel surfaces indicated that an oxidized nickel surface could support a weakly bound NO state not found on clean Ni(100). 

Fig. 4.4. a-d Laser-induced time-resolved luminescence spectra of apatite with uranyl (a-c) and luminescence (d) after oxidizing heating (possibly in fluorite inclusions)... 

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. 

Simeonsson, J. B G. W. Lemire, and R. C. Sausa, Laser-Induced Photofragmentation/Photoionization Spectrometry A Method for Detecting Ambient Oxides of Nitrogen, Anal. Chem., 66, 2272-2278 (1994). 

Fast-atom bombardment mass spectrometry (FAB-MS) has been applied to the identification of diterpenoid compounds and their oxidation products. Similarly, laser-induced desorption mass spectrometric (LDMS) techniques have been applied to the identification of natural and synthetic organic pigments in microscopic paint samples prepared as cross sections [60]. 

Combinatorial methods were also applied in the discovery of new catalysts for the low-temperature oxidation213 and oxidative dehydrogenation of propane.214 A 144-member catalyst library was screened by photothermal deflection spectroscopy and mass spectrometry to find the most active compositions of V-Al-Nb and Cr-Al-Nb oxides for the oxidative dehydrogenation of ethane.215 The ternary combination V(45)-Sn(45)-Mo(10)-O selected by laser-induced fluorescence imaging gave much higher yield than did V205 in the selective oxidation of naphthalene to naphthoquinone.216... 

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