Absorption, generally resonance

The N-N rotation in both NNO moieties of 4a-d could be observed with the aid of variable temperature H and 19F NMR spectra of 4c <1997JOC5619>. The structural nature of difluoroamino-diazocines 45 and 46 could be diagnosed by 19F NMR. The chemical shift of the fluorine signal for 45 was at 20.71 ppm, which is within the typical range (18-25 ppm) of internal mono(difluoroamino)alkanes whereas, 46 showed an absorption at 29.4 ppm compatible with an internal grw-bis(difluoroamino) derivatives, which generally resonated at 27-33 ppm <1998JOC1566>. 

Absorption spectrum generally has a wide spectrum width. By the irradiation of narrow-width laser light, molecules with absorption frequency resonant to the laser light are selectively excited, and a hole is formed in the absorption spectrum. This is called hole burning. 

L. W. Nordheim, The Theory of Resonance Absorptions, General Atomics, GAMD-638, San Diego, Calif., Jan. 6, 1959. 

In this section we will discuss more conventional spectroscopies absorption, emission and resonance Raman scattering. These spectroscopies are generally measured under single frequency conditions, and therefore our... 

A refinement of the ENDOR experiment is electron-nnclear-nnclear triple resonance, now commonly denoted TRIPLE. In TRIPLE experiments one monitors the effect of a simnltaneons excitation of two nnclear spm transitions on the level of the EPR absorption. Two versions, known as special TRIPLE (ST) and general TRIPLE (GT), are rontinely perfonned on connnercially available spectrometers. 

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) ... 

Band 3, 3-93y. (2548 cm. ). This absorption is characteristic of carboxylic acids and is due to the 0—H stretching absorption in the reson-ance-stabUised dimer. (Carboxylic acids generally exist as dimers in the solid state and in all but very dilute solutions.)... 

Laser Photochemistry. Photochemical appHcations of lasers generally employ tunable lasers which can be tuned to a specific absorption resonance of an atom or molecule (see Photochemical technology). Examples include the tunable dye laser in the ultraviolet, visible, and near-infrared portions of the spectmm the titanium-doped sapphire, Tfsapphire, laser in the visible and near infrared optical parametric oscillators in the visible and infrared and Line-tunable carbon dioxide lasers, which can be tuned with a wavelength-selective element to any of a large number of closely spaced lines in the infrared near 10 ]lni. 

It is generally believed that the absorption (and fluorescence excitation) peak at about 400 nm is caused by the neutral form of the chro-mophore, 5-(p-hydroxybenzylidene)imidazolin-4-one, and the one in the 450-500 nm region by the phenol anion of the chromophore that can resonate with the quinoid form, as shown below (R1 and R2 represent peptide chains). However, the emission of light takes place always from the excited anionic form, even if the excitation is done with the neutral form chromophore. This must be due to the protein environment that facilitates the ionization of the phenol group of the chromophore. This is also consistent with the fact that the pACa values of phenols in excited state are in an acidic range, between 3 and 5 (Becker, 1969), thus favoring anionic forms at neutral pH. 

The fact that the photon does traverse the lattice planes does not mean that the photon wUl be absorbed or even scattered by the solid. The reflectance of the photon is a function of the nature of the compositional surface, whereas absorption depends upon the interior composition of the solid. A "resonance" condition must exist before the photon can transfer energy to the solid (absorption of the photon), hi the following, we show this resonance condition in general terms of both R A. 

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