Electron attachment dissociative

2-3 complexes have been measured by negative-ion mass spectrometry, but the higher hydrates were not studied [19]. This type of research was also carried out for the hydrates and methanolates of the halides. The hydrates are important to atmospheric processes and will be discussed in Chapter 11. 

In unimolecular dissociation the experimental activation energy is an upper limit to the quantity -EDEA = D(R — Cl) — Ea(C 1). It was empirically observed that the activation energy was linearly related to EDEA with a slope of unity and approached zero for an exothermicity of about 13 kcal/mole or 0.6 eV. Thus, 

Only compounds that undergo sequential dissociative thermal electron attachment can exhibit a y region, where (k2 E kN) and (k-1 k2), and 

Since E2 is greater than Ea, there will be a change in the sign of the slope in the transition from the a to y region. The experimental quantity (Ea(RLe)—E2) is D(R — Le) — Ea(Le). In the (S and 8 regions K = k /lkD, and the ECD data define A and E. The specific regions observed will depend on the electron affinity of the dissociating species and the electron affinity of the compound. 

The data for o-FNB is the prototypical data for a compound that exhibits four temperature regions. In the case of o-F-nitrobenzene the A, E, and Ea values have been measured using other techniques, and the values of A2 and E2 have been measured experimentally or calculated [23, 24]. The only parameter that has not been measured by an independent procedure is Qan. All the quantities obtained from the ECD agree with values obtained by other techniques. In other words, the ECD response could have been calculated from properties measured in independent experiments if the value of Qan was assumed to be unity. 

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Anion solvation in alcohol clusters has been studied extensively (see Refs. 135 and 136 and references cited therein). Among the anions that can be solvated by alcohols, the free electron is certainly the most exotic one. It can be attached to neutral alcohol clusters [137], or a sodium atom picked up by the cluster may dissociate into a sodium cation and a more or less solvated electron [48]. Solvation of the electron by alcohols may help in understanding the classical solvent ammonia and the more related and reactive solvent water [138], By studying molecules with amine and alcohol functionalities [139] one may hope to unravel the essential differences between O- and N-solvents. One should note that dissociative electron attachment processes become more facile with an increasing number of O—H groups in the molecule [140],... 

The data shown in Fig. 2 suggest that the near vertical attachment of an electron into the S-S a orbital of MeS-SMe would require an electron with kinetic energy of ca. 0.9 eV and would generate the a anion on a reasonably repulsive part of its energy surface. This results in the well-known dissociative electron attachment (DBA) process [7,8] which has been well studied experimentally for MeS-SMe. Figure 2 also suggests that lower-energy electrons can attach to the a S-S orbital... 

Dissociative electron attachment (DEA) occurs when the molecular transient anion state is dissociative in the Franck-Condon (FC) region, the localization time is of the order of or larger than the time required for dissociation along a particular nuclear coordinate, and one of the resulting fragments has positive electron affinity. In this case, a stable atomic or molecular anion is formed along with one or more neutral species. Dissociative electron attachment usually occurs via the formation of core-excited resonances since these possess sufficiently long lifetimes to allow for dissociation of the anion before autoionization. 

APPLICATION OF DISSOCIATIVE ELECTRON ATTACHMENT TO THE CONSTRUCTION OF RADIATION RESIST... 

Dissociative electron attachment is a radiation chemical reaction suitable for cutting a polymer just in half. If two equivalent polymer skeletons R are connected with a functional group XY that has a large cross section of dissociative electron attachment, the polymer captures an ejected electron at the center of the polymer skeleton and is broken into two fragments with similar molecular weight, as R-XY-R + e —>R-X + Y-R. The key to construct such a polymer is to find a functional group that is possible to connect two polymer chains, to capture an electron efficiently, and to dissociate into two fragments after the capture. 

Figure 1 Schematic representation of the formation of polymer fragments by random scission (left) and selective scission by dissociative electron attachment (right).

Figure 2 Excitation (broken line, observed wavelength = 475 nm) and fluorescence (solid line, excitation wavelength = 320 nm) spectra of the benzyl radical generated in y-irradiated MTHF at 77 K by dissociative electron attachment to C2H5COOCH2C6H5.

As shown in Fig. 9, irradiation of neat polystyrene does not result in the efficient scission but increases the molecular weight due mainly to cross-linking, though a small bump at the low molecular weight side of the SEC pattern indicates the dissociative electron attachment. The cross-linking is suppressed by addition of hydroquinone as a radical scavenger, which suggests that combination reaction of polymer radicals takes place in the neat polymer, as... 

Although the irradiation of 200 kGy decomposes about 80% of polystyrene in toluene by the dissociative electron attachment, the yield of the decomposition is only 20% for solid toluene. Because of its low efficiency of scission, the coupled polystyrene may not be a polymer suitable as a radiation resist. However, the present study has shown that a polymer that can be decomposed into two equivalent skeletons by ionizing radiation is possible to be... 

A simple diagram depicting the differences between these two complementary theories is shown in Fig. 1, which represents reactions at zero driving force. Thus, the activation energy corresponds to the intrinsic barrier. Marcus theory assumes a harmonic potential for reactants and products and, in its simplest form, assumes that the reactant and product surfaces have the same curvature (Fig. la). In his derivation of the dissociative ET theory, Saveant assumed that the reactants should be described by a Morse potential and that the products should simply be the dissociative part of this potential (Fig. Ib). Some concerns about the latter condition have been raised. " On the other hand, comparison of experimental data pertaining to alkyl halides and peroxides (Section 3) with equations (7) and (8) seems to indicate that the simple model proposed by Saveant for the nuclear factor of the ET rate constant expression satisfactorily describes concerted dissociative reductions in the condensed phase. A similar treatment was used by Wentworth and coworkers to describe dissociative electron attachment to aromatic and alkyl halides in the gas phase. ... 

In the absence of a three-electron bond, it is possible that some interaction (Van der Waals, electrostatics, etc.) between the product radical and anion exists. This situation has been discussed in some detail for the interaction between a halide ion and an alkyl radical generated in the gas phase by dissociative electron attachment to an alkyl halide. " It is expected that these interactions will be more important in the gas phase, as a solvent tends to screen charge. Wentworth suggested that an appropriate potential... 

An early report (Briscese and Riveros, 1975) revealed that in the gas phase, alkoxide ions can displace fluoride from fluorobenzene (91). Hydroxide ion fails to react because C6H5F is more acidic than H20 and thus proton transfer becomes the most important channel. Similar reactions with other monohalobenzenes are complicated because these substrates usually generate halide ions directly by dissociative electron attachment. 

The opticol absorption spectra of the solvated electron have now been reported for a number of organic liquids. The chemical reactivity in the aliphatic alcohols has been studied by the pulse radiolysis method. The absorption maxima for a series of five aliphatic alcohols are in the visible to near infra-red. These maxima show a red shift with decrease in the static dielectric constant. The solvated electron undergoes reactions of electron-ion combination, electron attachment, and dissociative electron attachment. Absolute rate constants have been determined for these reactions. 

The absolute rate constants were determined for a variety of reactions of the solvated electron in ethanol and methanol. Three categories of reaction were investigated (a) ion-electron combination, (b) electron attachment, and (c) dissociative electron attachment. These bimolecular rate constants (3, 27, 28) are listed in Table III. The rate constants of four of these reactions have also been obtained for the hydrated electron in water. These are also listed in the table so that a comparison may be made for the four rate constants in the solvents ethanol, methanol, and water. 

The occurrence of the dissociative electron attachment reactions was also established by direct observation of the transient product. Thus, the absorption spectra of the benzyl radical (21, 28) and the triphenyl methyl radical (28) were both observed. The other products formed in... 

A water molecule contains two hydrogen atoms and one oxygen atom. Hydrogen and hydroxyl radicals can be produced from the dissociation [93] or dissociative electron attachment of water [94] ... 

In a number of reactions that are written as dissociative electron attachments, short-lived radical anions are in fact intermediates. A case in point is 5BrUra (Chap. 10). An interesting behavior is shown by the radical anion of N-bromo-succinimide which does not release a bromide ion but rather fragments into a bromine atom and a succinimide anion [reactions (17) and (18)] (Lind et al. 1991). 

D.J. Haxton, C.W. McCurdy, T.N. Rescigno, Dissociative electron attachment to the H2O molecule I. Complex-valued potential-energy surfaces for the 2I1, 2A, and 2B2 metastable states of the water anion, Phys. Rev. A 75 (2007) 012710/1. 

The best-known reactions are those of electron attachment and dissociative electron attachment, since these are the reactions... 

Chloromethylated polystyrene and chloromethylated poly(a-methyIstyrene) are negative type resists having high sensitivity and high resolution. In the pulse radiolysis of solid films of this polymer, the absorption spectra of substituted benzyl-type polymer-radical and the charge transfer complex between phenyl rings and chlorine atoms were observed (Fig. 17) [59], The benzyl-type radical may be produced by the dissociative electron attachment to the benzyl part of chloromethylated polystyrene (CMS). 

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