Laser resonance absorption

Advanced electro-optical methods (e.g., laser resonance absorption) capable of measuring average concentrations over long distances still requite extensive research and field testing to demonstrate their practical application to ozone monitoring. Because electro-optical methods have not yet been widely used, they are not discussed further here. 

Carbon Monoxide Laser Resonance Absorption Studies of 0(3P) + 1-Alkynes and Methylene Radical Reactions... 

The CO laser resonance absorption technique is a useful tool for studying the dynamics of chemical reactions that involve the initial production of vibrationally excited CO molecules. We have recently applied this technique to study various atomic and free radical reactions related to combustion and electronic-to-vibrational energy transfer processes U—6). In this brief account, we discuss mainly the dynamics of 0(3P) + 1-alkynes and associated free radical reactions. 

Figure 1. A schematic for the CO laser resonance absorption apparatus...

The gas-phase UV spectrum of GeMe2 generated from two different precursors has been recorded by laser resonance absorption flash kinetic spectroscopy106. The identity of the germylene was supported by chemical trapping experiment and by analysis of the stable end products of the decomposition of the chosen precursors. 

LRAFKS laser resonance absorption flash kinetic spectroscopy... 

Time-resolved CO laser resonance absorption used to 518 study vibrational energy disposal pattern in CO following photofragmentation of 3-cyclopentenone 220—270 nm photolysis of succinic anhydride shown to 519 produce COj, CO, and CjH but not in quantities... 

Kinetics of reactions of Fe(CO), (x = 2, 3, 4) with CO. 547 Co-ordinatively unsaturated intn carbonyls generated by exclmer laser flash photolysis of FelCO) and monitored using CW CO laser resonance absorption Competition between photofragmentation and photo- 548 ionization of jet-cooled FefCO) used to obtain excited-state lifetimes in the wavelength range 290—310 nm. 

NH2 radicals are formed in the troposphere by reaction of OH radicals with NH2, and may be formed in the stratosphere by solar photolysis of NHj at u.v. wavelengths <220 nm. The kinetics of NH2 radical reactions with O2 and O3 have been studied by Patrick and Golden using a laser photolysis/laser resonance absorption arrangement. They obtained an upper limit of 1.5 x 10 cm molecule s for the third-order combination of NH2 and O2 which contrasts with the value of 3.5 x 10" cm molecule s reported by Hack et al. Andresen et al7 obtained rate data for the reaction of NH2 with NO, monitoring the products using various detection techniques, and Whyte and Phillips determined rate constants for the reactions NH2 + N, NH2+NO, and NH2+NO2. 

But where does the available energy go, if not into OH V, R excitation Is it in center-of-mass (CM) translation, and/or CO V, R excitation These questions were answered experimentally by both (i) LIF measurements of nascent OH Doppler shifts, which yielded average laboratory translational energies, which in turn were converted to average CM translational energies [122], as well as (ii) infrared diode laser resonance absorption [123] and VUVLIF [124] measurements of nascent CO K R excitation. With (i), several well-resolved OH v = 0) - X H rotational transitions were... 

Those combustion reactions described here are best studied by the flash photolysis-laser resonance absorption technique. Other well-established techniques (such as chemiluminescence) are less useful for these cases because free-radical species cannot be cleanly produced by microwave and electrical discharge methods. 

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... 

In order to understand the dynamics of the 0 + CF reaction occurring in the SO2 - CFBr3 chemical CO laser system, we carried out CO laser resonance absorption experiments to measure the vibrational energy distribution of the CO formed in the reaction. A detailed description of the flash-photolytic CO laser-probing system can be found in reference (19). Experiments were carried out using both Suprasil ( S 165 nm) and quartz ( - 200 nm) flash tubes for mixtures of CFBr3 SOj with He as a diluent. With the Suprasil tube, 10-torr samples of a 1 1 98/CFBr3 SO2 He mixture were used, whereas with the quartz tube 5-torr samples of both the 1 1 98 and 1 1 48 mixtures... 

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