Benzyl radical, absorption spectrum

The 7T system of PN is closely related to that of the benzyl and anilino radicals. Thus, it is no surprise that the triplet absorption spectrum of PN is very similar to the experimental spectra of the benzyl (CgHsCH ) and anilino (CfiHsNH ) radicals. Benzyl radical has a medium intensity feature at 316 nm and a very weak band at 452 nm. The anilino radical has a medium intensity band at 308 nm and a weak transition at 400 nm. ... 

Reaction Scheme of CMS Resists. The transient absorption spectrum shown in Figure 6 and observed for irradiated CMS films is mainly composed of two components as based on pulse radiolysis data of solid films of CMS and polystyrene, and CMS and polystyrene solutions in cyclohexane, chloroform, and carbon tetrachloride. An absorption with a maxima at 320 nm and 500 nm as due to the charge transfer radical-complex of the phenyl ring of CMS and chlorine atom (see Figure 14) and an absorption with maxima at 312 and 324 nm is due to benzyl type radicals (see Figure 11). 

The high sensitivity of SNR resist to electron beam and deep UV radiation (23,24) is again due to the high efficiency of the pair production of two polymer radicals ( Pi and Pi) at sites close to each other through reactions involving both excited and ionic species. The benzyl type polymer radical ( P ) and complexes are clearly identifiable from the time-resolved absorption spectrum data (5 b) shown in Fig. 3. 

Quite a number of workers have examined specific aspect of the direct photolysis of substituted benzenes and, although the mechanisms are not fully understood, some important conclusions have been reached. Hentz and Burton examined the photolysis of toluene, ethyl benzene and mesitylene in both liquid and vapor states using a medium-pressure mercury lamp. They concluded that the gas-phase products, hydrogen, methane and ethane, were formed with a quantum yield of about 10 , while polymer formation was much more important. At 150 °C hydrogen was the most important gas-phase product except for the case of ethyl benzene in the vapour, where both methane and ethane were more important than hydrogen. Porter and Wright have shown by flash photolysis that benzyl radicals are formed in the photolysis of toluene and ethyl benzene and have observed the absorption spectrum of the benzyl radical. 

At this point it is worth considering the spectrum of the benzyl radical [76]. The electronic absorption spectrum of the benzyl radical consists of a strong sharp band at 312nm and a weak forbidden band at 450nm. The absorption spectrum of the anilino radical is also known and it very much resembles that of benzyl [77], The anilino radical has a strong sharp absorption band at 308 nm. The major difference in the spectra of anilino and benzyl radical is that the forbidden band in benzyl is much more intense in the anilino radical and it is shifted to 400 nm. It has been found that the... 

The latter point is not trivial. Recall that Reiser et al [18] reported in 1965 that photolysis of phenyl azide in an organic glass produces a new UV-VIS absorption spectrum. The spectrum was attributed to triplet phenyl nitrene because of Wasserman s [63] EPR work and the similarity of the spectrum to that of benzyl and anilino radical. However after Chapman and Le Roux s work appeared one could legitimately ask whether Reiser s spectrum is that of triplet phenyl nitrene or of dehydroazepine, or a mixture of both species. 

The n system of 49 is closely related to that of the benzyl and aniline radicals. Thus, it is no surprise that the triplet absorption spectrum of M9 is very similar to the experimental... 

The photodecarboxylation mechanism of simple arylacetic acids is not completely understood due to the relatively low quantum yields of reaction (O < 0.06). The formation of benzyUc radicals (which show a transient absorption spectrum, with -315 nm) has been taken as evidence for the homolytic cleavage of the undissociated acid. By contrast, photolysis of carboxylate forms gives rise to carbanion intermediates -350 nm) via heterolytic cleavage (Scheme 1). However, the possibility of initial electron photoejection and subsequent homolytic decarboxylation (eventually followed by recombination of the electron with the benzyl radical) cannot be ruled out, as the hydrated electron has been observed as a transient species. ... 

Pulse radiolysis has been used to afford the radical cations of thioanisole, p-methylthioanisole, and benzyl phenyl sulfides. The absorption spectra of these radicals and their reaction with a number of nucleophiles and electron donor s are reported.302 Exposure of trimethylphosphine sulfide to 60Co 7-radiation at 77 K gave the radical anion Me3PS , identified by its ESR spectrum, from which other radicals, including Me2PS, were formed at higher temperatures.303... 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

The two sharp absorption peaks ((Fig. 1), spectrum b) are characteristic of a substituted benzyl type polymer radical ( Pi) (14). The formation rate of these peaks is very rapid (within the limitation of the detection system) and is faster than the decay rates of the excimer fluorescence and the broad absorption between 300 and 400 nm (T Ti absorption) described below. There was no clear correlation between the increase in the absorption peak attributed to Pi and the decay of the excimer and triplet species of CMS suggesting that some other species is the main precursor of P ... 

Commercially used plasticizers such as di n-octyl adipate, di -octyl sebacate, di(2-ethylhexyl)phthalate and butyl benzyl phthalate can contribute to the photo-dehydrochlorination of poly(vinyl chloride) and this is attributed to a free radical mechanism, whereby a radical is first formed in the plasticizer and then transferred to the polymer [255, 297, 298, 688, 1636, 2270]. In the case ofdi(2-ethylhexyl)phthalate and tri(2-ethylhexyl)trimellitate the observed effects are even more drastic under conditions of solar irradiation [554]. This effect has been attributed to the fact that the trimellitate exhibits a much greater absorption in the wavelength range of the solar spectrum and hence is more likely to form free radicals. 

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