Direct absorption

Recently, the state-selective detection of reaction products tluough infrared absorption on vibrational transitions has been achieved and applied to the study of HF products from the F + H2 reaction by Nesbitt and co-workers (Chapman et al [7]). The relatively low sensitivity for direct absorption has been circumvented by the use of a multi-pass absorption arrangement with a narrow-band tunable infrared laser and dual beam differential detection of the incident and transmission beams on matched detectors. A particular advantage of probing the products tluough absorption is that the absolute concentration of the product molecules in a given vibration-rotation state can be detenuined. 

Chapman W B, Blackman B W, Nizkorodov S and Nesbitt D J 1998 Quantum-state resolved reactive scattering of F + H2 in supersonic jets Nascent HF(v,J) rovibrational distributions via IR laser direct absorption methods J. Chem. Rhys. 109 9306-17... 

B2.5.351 after multiphoton excitation via the CF stretching vibration at 1070 cm. More than 17 photons are needed to break the C-I bond, a typical value in IR laser chemistry. Contributions from direct absorption (i) are insignificant, so that the process almost exclusively follows the quasi-resonant mechanism (iii), which can be treated by generalized first-order kinetics. As an example, figure B2.5.15 illustrates the fonnation of I atoms (upper trace) during excitation with the pulse sequence of a mode-coupled CO2 laser (lower trace). In addition to the mtensity, /, the fluence, F, of radiation is a very important parameter in IR laser chemistry (and more generally in nuiltiphoton excitation) ... 

Some of the target molecules gain so much excess internal energy in a short space of time that they lose an electron and become ions. These are the molecular cation-radicals found in mass spectrometry by the direct absorption of radiation. However, these initial ions may react with accompanying neutral molecules, as in chemical ionization, to produce protonated molecules. 

When recording excitation and fluorescence spectra it must be ensured that monochromatic light falls on the detector This can best be verified in instruments built up on the kit principle or in those equipped with two monochromators (spectrofluonmeters) The majority of scanners commercially available at the moment do not allow of such an optical train, which was realized in the KM3 chromatogram spectrometer (Zeiss) So such units are not able to generate direct absorption or fluorescence spectra for the charactenzation of fluorescent components... 

Cineol by Direct Absorption with Resorcin Solution. Cineol by Absorption with Resorcin after Fractionation. Cineol by Phosphoric Acid Process. 

Volkov and Sushko [335] described a technique that is based on the use of nets. This method provides direct absorption spectra, but is very complex to perform The net must be placed in a chamber that ensures a pure inert atmosphere so as to avoid hydrolysis of the melt, and the temperature and geometry of the net must be kept very stable. Other major limitations of the method are the requirements that the surface tension of the melt be such that its position on the net is ensured, and that the vapor pressure of the material in molten state be as low as possible... 

Later, when nitric acid was manufd from synthetic ammonia at relatively low cost, synthetic sodium nitrate was made from it either thru the reaction between nitric acid and soda ash, or by direct absorption of nitrogen dioxide in an aq soln of Na carbonate (see above equation). The Na nitrate-nitrite soln was then heated with excess nitric acid to convert the nitrite to nitrate, and the NO thus produced was recycled to the nitric acid plant (Ref 6)... 

The major routes of uptake of xenobiotics by animals and plants are discussed in Chapter 4, Section 4.1. With animals, there is an important distinction between terrestrial species, on the one hand, and aquatic invertebrates and fish on the other. The latter readily absorb many xenobiotics directly from ambient water or sediment across permeable respiratory surfaces (e.g., gills). Some amphibia (e.g., frogs) readily absorb such compounds across permeable skin. By contrast, many aquatic vertebrates, such as whales and seabirds, absorb little by this route. In lung-breathing organisms, direct absorption from water across exposed respiratory membranes is not an important route of uptake. 

Instead of making use of direct absorption of the excitation energy by the molecule being analyzed it is possible (as is the case of oxygen... 

Table 3.23 gives an overview of the vessel types in use for microwave applications. It is especially important to distinguish between open vessel (as used in Sox wave ) and closed vessel (pressurised) microwave heating systems (as in MAE). Both open-vessel and closed-vessel microwave systems use direct absorption of microwave radiation through essentially microwave transparent vessel materials (Teflon, PC). 

In order to perform extraction of additives or dissolution of polymers, solvents that absorb microwave energy are necessary. This is more important than direct absorption of microwave energy by the polymer or additives. When microwave extraction of additives... 

For a triplet to result, two electrons must have different orbitals and the same spin (the Pauli principle forbids having two unpaired electrons in the same orbital since all four quantum numbers would be the same). We saw in Chapter 1 that upon light absorption an electron is promoted from one orbital to a higher orbital. If we were to excite directly from the ground state singlet to the triplet state we would have to simultaneously change orbitals and electronic spins. Since this process is relatively improbable, direct absorption to the triplet state is seldom observed (later in this chapter,... 

C, excitation at 289 nm, emission observed at 525 nm, degassed films. (l2) Measured total phosphorescence intensity of MBC (arbitrary units) ("I, X y) component of the MBC phosphorescence due to direct absorption of MBC molecules (ltenJ component of the MBC phosphorescence due to energy transfer. 

Table 5.5 Prominent peaks in the mass spectrum of aloe resin (see Figure 5.13), interpretation following the literature. The dyes are not detected as sodium adducts but as radical cations formed by direct absorption and ionisation of the laser energy...

Class D substances and with a 10 h half-time for Class W and Class Y substances. Absorption of material directly into blood is predicted to occur with a 15 min half-time for all compounds. Direct absorption is predicted for 0.5 of the Class D material, for 0.1 of the Class W material, and for 0.01 of the Class Y material. Cuddihy and Ozog (1973) studied direct absorption of 144CeCl3 solutions deposited in the nasal region of Syrian hamsters. About 0.04 of the deposited radiocerium was absorbed through the nasal membranes into the blood. This is about one-half of that predicted by the Task Group Model for nasal absorption of Class W compounds in humans. 

From comparison of the data presented in Table 2.2 [8], it is obvious that the energy of the microwave photon at a frequency of 2.45 GHz (0.0016 eV) is too low to cleave molecular bonds and is also lower than Brownian motion. It is therefore clear that microwaves cannot induce chemical reactions by direct absorption of electromagnetic energy, as opposed to ultraviolet and visible radiation (photochemistry). 

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