Spectral efficiency, apparent

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

This is a method which is very attractive in principle and which has been applied to yield approximate barriers for a number of molecules. There are, however, difficulties in its use. In the first place, it is not easy to measure the intensities of microwave lines with accuracy. There are unsolved problems of saturation, reflections in the wave guide, and variation of detector efficiency with frequency which are presumably reponsible for the fact that measurements made with ordinary wave guide spectrometers are not very reproducible. In addition, both the spectral lines may be split into components by tunnelling from one potential minimum to another and this splitting, even though it is not resolved, can alter the apparent intensity. Furthermore, it is often difficult to find pairs of lines such that neither is obscured by Stark lobes from the other. 

The effective biological dose (Ee 18) at local apparent noon for each chamber was estimated by multiplying the relative biological efficiency for photoinhibition [epi(X)] by the available spectral irradiance [E(X)], and integrating with respect to wavelength (X, 290-400 nm) ... 

Based on the PVK FDEANST system, the PR performance as a function of the photosensitizer has been studied [54], It is apparent that varying the sensitizer changes the photogeneration rate and greatly influences both optical gain and diffraction efficiency. By replacing TNF with TNFDM, the spectral sensitivity of composites can be extended to the near infrared (IR) region. 

More recently, Faughnan and Hanak (1983) have used spectral response data to determine that the concentration of acceptors is —1019 cm-3 for p-type a-Si H layers containing — 1021 boron atoms cm -3 (as determined by SIMS) for a doping efficiency of — 1 %. Dresner (1983) has estimated that the doping efficiency of boron in a-Si H is — 0.1 % for films containing between 1019 and 1021 boron atoms cm-3. Thus, more recent estimates of the doping efficiency are in the range 0.1-1.0%. Apparently, many of the dopant atoms do not go into electronically active substitutional sites. 

In course of subsequent work Bubeck, Tieke, and Wegner discovered that the action spectrum for photopolymerization of undoped diacetylene multilayers extends into the visible provided some polymer formed in course of previous UV-irradiation is present. Since obviously excitation of the polymer can sensitize the reaction this effect has been termed self-sensitization. Checking the absorption spectrum of the polymer produced via self-sensitization assured that the final product is identical with the product obtained under UV excitation of the monomer. Later work by Braunschweig and Bassler demonstrated, that the effect is not confined to multilayer systems but is also present in partially polymerized single crystalline TS-6, albeit with lower efficiency. Interestingly, the action spectrum of self-sensitization follows the action spectrum for excitation of an electron from the valence band of the polymer backbone to the conduction band rather than the excitonic absorption spectrum of the polymer which is the dominant spectral feature in the visible (see Fig. 21). The quantum yield is independent of the electric field, whereas in a onedimensional system the yield of free carriers, determined by thermal dissociation of optically produced, weakly bound geminate electron-hole pairs, is an linear function of an applied electric field 29.30,32,129) Apparently, the sensitizing action does not... 

At some point, however, assay recovery for an LC/MS method will be estimated and when this is done several important points are worth keeping in mind. Over the instrument linear range, mass spectral response is proportional to the number of ions which have entered the high vacuum region of the instrument. This number of ions is, in turn, dependent on how efficiently an analyte is ionized in the source. For a given analyte, the extent of ionization dictates its ability to compete with the matrix components present. As the amount of ionizable matrix components increases, the ability of an analyte to ionize, hence its apparent concentration, is diminished. This so-called ionisation suppression, or ion suppression, can lead to nonquantitative behavior in LC/MS [51,52],... 

The same spectral evolutions were observed for the silicas mixed with KBr, pretreated in the DR cell at high temperature, and then cooled down to room temperature. The successive variations of the vOH absorptions are shown in Figure 3 for silicas G and P. An apparent temperature of 500 °C is necessary to eliminate the most strongly H-bonded silanols (curve a). In contrast, the distribution of weakly perturbed silanols is desorbed between 540 and 580 °C (curve c), which corresponds to a rapidly increasing efficiency of the treatment above 540 °C. After a treatment at the apparent temperature of 580 °C, the i/OH profiles are similar to those of self-supporting silica disks pretreated at the real temperature of 645 °C. An intermediate distribution of desorbed silanols, with two broad peaks at about 3570 and 3675 cm-1, is. also shown in Figure 3 (curve b). 

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