Ultraviolet laser studies

Tunable visible and ultraviolet lasers were available well before tunable infrared and far-infrared lasers. There are many complexes that contain monomers with visible and near-UV spectra. The earliest experiments to give detailed dynamical infonnation on complexes were in fact those of Smalley et al [22], who observed laser-induced fluorescence (LIF) spectra of He-l2 complexes. They excited the complex in the I2 B <—A band, and were able to produce excited-state complexes containing 5-state I2 in a wide range of vibrational states. From line w idths and dispersed fluorescence spectra, they were able to study the rates and pathways of dissociation. Such work was subsequently extended to many other systems, including the rare gas-Cl2 systems, and has given quite detailed infonnation on potential energy surfaces [231. 

Young et al. (2002a) showed that ultraviolet laser ablation combined with MC-ICPMS (LA-MC-ICPMS) can offer advantages over other methods of spatially resolved Mg isotopic analysis of meteorite materials. They collected data for chondrules and a CAI from the Allende meteorite. Each datum in that study represents approximately 2.8 pg of material (based on a laser spot diameter of 100 pm and laser pit depth of 30 pm depths are uncertain to + 20%). 

ELBI effect on the morphology of erythrocytes was studied in seven rabbits. ELBI was performed by introducing the waveguide into the lumen of the femoral vein under ether anesthesia. He-Ne laser LG-75 (HNL), Russia, and nitrogen ultraviolet laser LGI-21 (UVL) were used. The power of radiation at the end of waveguide was 2.5 mW, and irradiation was applied for one hour. 

Bamford et al. (45) have recently studied the photolysis of H2CO near the S- origin. The complete rotational distribution has been obtained for CO, which was detected by vacuum ultraviolet laser induced fluorescence. The distribution has a peak at J" = 42 and highly nonthermal, suggesting that energy randomization does not occur during dissociation. The population in CO J" < 20 is absent. The vibrational population of v" = 1 is 14 5% as large as that of CO (v" = 0). The C0(v" = 1) has nearly the same rotational distribution as C0(v" = 0). 

Vacuum ultraviolet photochemistry can also be studied by using near ultraviolet lasers of high intensity to excite 2-photon transitions in the parent molecule. An elegant early experiment was that of Wang and Davis which utilised a frequency-doubled dye laser at 300 nm to excite amultaneously the biphotonic dissociation of H2O (effectively at 150 nm, in the A -continuum) and the single photon (A - X) fluorescence of the resultant OH fragments found along the axis of the focussed laser beam. 

The application of the quasi-cw, ultraviolet laser source to kinetic studies was demonstrated in the laser photolysis/laser-induced fluorescence experiments shown schematically in Figure 2. Chemical reactions were initiated by 193-nm photolysis of N2O in N20/H20/hydrocarbon/helium gas mixtures. The 0( D) atoms formed by photodissociation rapidly converted to OH through reaction with H2O, and time-resolved OH concentrations were measured as functions of hydrocarbon number density by laser-induced fluorescence. Hydroxyl radical fluorescence was excited by pumping the nearly coincident Pjl, Qi3, and Qi3 (0,0) band transitions at 308.16 nm, (15) and radiation emanating from the reaction volume in a downward direction was skimmed by black-anodized collimators, focused by quartz lenses, selected by a bandpass filter (308.3 nm peak, 8 nm FWHM), and detected by an RCA 8850 photomultiplier operating in the photon-counting mode. 

In many respects the development of tunable infrared and ultraviolet laser sources when combined with molecular beam expansions, mrurked the start of the modern or contemporary period of cluster studies. First, it offered the opportunity to selectively excite specific rovibrational or rovibronic levels in a complex. Second, variations in the spectra (linewidth, intensity and frequency) gave insight into dynamical behavior and the presence of nearby perturbing states. 3 Finally, the availability of widely tunable sources has enabled the experimentalist to select quantum states that would provide the maximum information content on a cluster system, an impetus that continues to drive the development of new lasers and laser systems. As this is an extremely wide field of research, primary emphasis in this chapter will be placed on vibrational spectroscopic studies of neutral and ionic clusters. 

Nonami, H. Fukui, S. Erra-Balsells, R. P-Carboline alkaloids as matrices for matrix-assisted ultraviolet laser desorption time-of-flight mass spectrometry of proteins and sulfated oligosaccharides a comparative study using phenylcarbonyl compounds, carbazoles and classical matrices. J. Mass Spectrom. 1997, 32, 287 296. 

Giapintzakis, J., Sfounis, A., and Velegrakis, M. (1999) A comparative mass spectroscopic study between infrared and ultraviolet laser ablation of a superconducting YBa2Cu307 j target. Int. J. Mass Spectrom., Ion Processes, 189,1—7. 

For OH -f MB, there are several experimental measurements " of the total rate constant at ambient and low temperatures. At high temperatures, Lam et al. " have measured in 2012 the overall rate for MB and several other small esters at 876—1371 K in shock tube studies by following decays of the OH signal using ultraviolet laser absorption. Theoretical rates for OH -f MB are available from Huynh and VioH ° and Zhang et al. and include information on the abstraction sites that is not available from... 

Optical metiiods, in both bulb and beam expermrents, have been employed to detemiine tlie relative populations of individual internal quantum states of products of chemical reactions. Most connnonly, such methods employ a transition to an excited electronic, rather than vibrational, level of tlie molecule. Molecular electronic transitions occur in the visible and ultraviolet, and detection of emission in these spectral regions can be accomplished much more sensitively than in the infrared, where vibrational transitions occur. In addition to their use in the study of collisional reaction dynamics, laser spectroscopic methods have been widely applied for the measurement of temperature and species concentrations in many different kinds of reaction media, including combustion media [31] and atmospheric chemistry [32]. 

No information was found on the transformation of diisopropyl methylphosphonate in the atmosphere. Based on the results of environmental fate studies of diisopropyl methylphosphonate in distilled water and natural water, photolysis (either direct or indirect) is not important in the transformation of diisopropyl methylphosphonate in aquatic systems (Spanggord et al. 1979). The ultraviolet and infrared laser-induced photodegradation of diisopropyl methylphosphonate in both the vapor or liquid phase has been demonstrated (Radziemski 1981). Light hydrocarbon gases were the principal decomposition products. Hydrogen, carbon monoxide (CO), carbon dioxide (C02), and water were also detected. 

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