Photolysis spectral data

Characteristically, the mechanisms formulated for azide decompositions involve [693,717] exciton formation and/or the participation of mobile electrons, positive holes and interstitial ions. Information concerning the energy requirements for the production, mobility and other relevant properties of these lattice imperfections can often be obtained from spectral data and electrical measurements. The interpretation of decomposition kinetics has often been profitably considered with reference to rates of photolysis. Accordingly, proposed reaction mechanisms have included consideration of trapping, transportation and interactions between possible energetic participants, and the steps involved can be characterized in greater detail than has been found possible in the decompositions of most other types of solids. 

Figure 10. Spectral data in the frequency region of 500-3200cm 1 resulting from the photolysis of a mixture containing Br2 (20 ppm), CH3CHO (4.88 ppm) and NOz (3.25 ppm) in 700Torr of air. Values in parentheses are concentrations in ppm (1 ppm = 2.46x 1013 molecule cm 3).

The spectral data obtained from the photolysis of n-C4H9ONO (5.7 ppm) in 1 Torr of 02 and 700Torr of N2 are illustrated in Figure 13. The low 02 pressure used in this run was chosen to make reaction (28) dominant over... 

The photolysis of the phenylsilyltriazide 333 in a matrix indicated, based on UV and infrared absorption spectral data, the formation of compound 334, the first example of an isolated compound containing a triple bond to silicon169. Further irradiation (or thermolysis) of 334 led to an isomer, 335, believed to be the analog of an isonitrile. Both these compounds were characterized spectroscopically, and were trapped with t-butyl alcohol (equation 31). 

The synthesis of isomeric l,2,3,4-tetrakis(methyl-thio)hexafluoro-n-butane was finally achieved by photoassisted sonication, after the numerous attempts through the various methods had failed. A successful method described here consists of reacting trans-1,4-bis(methylth1o)hexafluoro-2-bu-tene in an excess of methyl disulfide with an added appropriate gas (hexafluoropropane) to increase and control the pressure in the reaction vessel. The heterogeneous mixture was then subjected to the combined photolysis and sonication at 50°C. The iaFNMR and mass spectral data of the product and the by-product l,2,4-tris(methylth1o)-3-H-hexafluo-ro-n-butane were presented. 

Fullerene silacyclopropane derivative (102) was prepared in 58% yield by photolysis of trisilane (101) in the presence of C60. The spectral data for the product was consistent with a silacyclopropane of C2v symmetry, which would arise from addition of the silylene across the six-ring-six-ring junction (Scheme 34) <93JA1605>. 

Shimizu et al report that while [2.2] paracyclophane (55) undergoes two-photon dissociation in low temperature matrices by way of the triplet state, in the gas phase, the efficient two-photon process proceeds via a hot molecule formed by internal conversion from the initially formed singlet excited state. The photocleavage of 2-nitrobenzyl ethers and ester has been widely reported and has now been evaluated as a deprotection methodology for indoles, benzimidazole, and 6-chlorouracil (Voelker et al). The mechanism of the cleavage of such compounds is considered to involve the o-quinonoid intermediate, but previously these had only been deduced from transient electronic spectra produced in flash photolysis experiments. Infrared spectral data from photochemical studies of 2-nitrobenzyl methyl ether in argon and nitrogen matrices have now been published which confirm that the intermediate does indeed have the o-quinonoid structure... 

The objectives of this study were to determine the photolysis rates of phenol and some chlorophenols in estuarine and distilled water under natural sunlight conditions. Effects of sunlight irra-diance, pH, and chloride ions concentration on photolysis rates were determined. Spectral data and sunlight photolysis rate constants of both the actinometer and the chlorophenols were used to calculate the apparent quantum yields of the various chlorophenols. 

Apparent Quantum Yield (0 ) of the Direct Photolysis of Chloro-phenols. The spectral data and sunlight photolysis rate constants of both actinometer valerophenone and the compound, and reaction quantum yield of valerophenone were used to calculate 0 of chlorophenols using GCSOLAR program (13). 

Table I records the molar extinction coefficient (e ) at various wavelengths (A), of solutions of PCDDs 1-4. Water-acetonitrile (2 3 v/v) was used as a solvent for compounds 1-3 whereas, in the case of Og-CDD 4, the solvent was neat acetonitrile. These spectral data were used in the prediction of the direct sunlight photolysis rates, i.e., kgp and corresponding half-life (L3/2)sp) pollutants 1-4...

Two-phase experiments. We conducted a photolysis experiment in which 1-naphthol was dissolved in a small amount of cyclohexane and layered over a pH 7 buffer. The partition coefficient for 1-naphthol between these two solvents favored cyclohexane by about 5 1. In this experiment, UV spectral data indicated that to some extent the photoreactions developed product distributions that would have occurred if the other phase had been absent. Thus, in the water layer, which did not contain much 1-naphthol to begin with because of the unfavorable partition coefficient, the usual maximum at 264 nm appeared and increased in intensity as it did in the single-phase aqueous experiments. In the cyclohexane layer, the loss of the 292-nm maximum for l-naphthol was observed as before, but a minor peak at 270 nm could also be observed. Also, the end absorption intensity decreased with time, probably because nonpolar photooxidation products were... 

CF2 CFa CF2 CF SAg (not isolated) -- (with EtI at 75 °C) CF2 CF2 CF2 CF SEt (21%). Raman and photoelectron spectral data are available for some CFs S-compounds, and so are e.s.r. parameters for the radical CFs S CHs-CBu a [generated via photolysis of a solution of the appropriate olefin in (CFs-S)2]. Unsuccessful attempts have been made to generate a radical anion via electrochemical or chemical (NaK alloy) reduction of 3,4-bis(tri luoromethyl)-l,2-dithieten. i Reactions between trifluoromethanesulphenyl chloride and JV-chloro-amines are portrayed in Scheme 26 (p. 216) and some involving hexafluorothioacetone dimer in Scheme 27 (p. 217) many unsuccessful attempts are claimed to have been made to isolate bis(trifluoromethyl)methanethiol from the products of the reactions of the dimer with amines, the conversion into hexafluoroisopropylidenimines being... 

Schaniel et al. studied the photolysis products of some [(NH3)4Pt(NO)X] (X = C1, S04 , NO3 complexes) (F ure 21) (132,133). They reported the first photogeneration of nitrosyl linkage isomers in such Pt nitrosyl complexes, from irradiation of a powdered sample of the [(NH3)4Pt(NO)Cl] complex with h t in the spectral range 550—800 nm. IR spectral data revealed a surprising shift in the 1/440 band from 1673 to 1793 cm that they attributed to a nitrosyl-to-isonitrosyl linkage isomerization to a geometry between / -ON and // -ON (132). 

PROBLEM 15.84 Upon direct photolysis or heating at 220 °C, the dimer of 2,5-dimethyl-3,4-diphenyl-2,4-cyclopentadien-1-one (A) yields compound B, mp 166-168 °C. Spectral data for compound B are summarized on the next page. Deduce the structure of compound B and explain your reasoning. (You may have to make an educated guess about the acmal stereochemistry of B.)... 

Much attention has been devoted to the development of methods to generate quinone methides photochemically,1,19-20 since this provides temporal and spatial control over their formation (and subsequent reaction). In addition, the ability to photogenerate quinone methides enables their study using time-resolved absorption techniques (such as nanosecond laser flash photolysis (LFP)).21 This chapter covers the most important methods for the photogeneration of ortho-, meta-, and para-quinone methides. In addition, spectral and reactivity data are discussed for quinone methides that are characterized by LFP. 

Normally, time-resolved FT-IR spectroscopy (TRS FT-IR) possesses the same data characteristics. In a typical TRS FT-IR experiment, interferograms are assembled for a specific delay time after the photolysis pulse, and the data produced are normally finer-grained in frequency than in time. This type of experiment is complementary to experiments with fine-grained time information. It is particularly useful where a wide spectral range is necessary and works reasonably well for highly reproducible events which occur on relatively long timescales (fractions of seconds) (83). It is also an appealing system for use on shorter timescales, and it has... 

Fig. 3. Data points indicate the course of the photolysis reaction of B2H6/O2 mixture monitored by mass spectral sampling of the reaction products (apparatus of F . 2).

The absolute values of the absorption cross sections of HCHO have been somewhat controversial. This appears to be due to a lack of sufficient resolution in some studies as discussed in Chapter 3.B.2, if the spectral resolution is too low relative to the bandwidth, nonlinear Beer-Lambert plots result. The strongly banded structure means that calculations of the photolysis rate constant require actinic flux data that have much finer resolution than the 2- to 5-nm intervals for which these flux data are given in Chapter 3 or, alternatively, that the measured absorption cross sections must be appropriately averaged. One significant advantage of the highly structured absorption of HCHO is that it can be used to measure low concentrations of this important aldehyde in the atmosphere by UV absorption (see Sections A.ld and A.4f in Chapter 11.). 

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