Transmission Electron Spectroscopy

In a very simple fonn of electron spectroscopy, known as electron transmission spectroscopy, the attenuation of an essentially monoenergetic beam of electrons is measured after passage tlnough a sample. If the target is very thin or of such low density that most electrons pass tlnough unscattered, the attenuation is small and the... 

Modelli and coworkers126 studied by PES and ETS (electron transmission spectroscopy) some silicon and tin derivatives of thiophene and furan, with the aim of following the energy gap between the HOMO and the LUMO as a function of the substituents. In particular they investigated the following tin derivatives ... 

Photoelectron and electron transmission spectroscopy indicate that there is appreciable interaction between the acetylene units of [129] (Houk et al., 1985). Both homoconjugation and hyperconjugation are proposed. Dewar and Holloway (1984) suggest that the through-bond interactions dominate. Similar thermochemical studies to those performed with the triquinacene series were carried out on [129] and some acyclic homoconjugated acetylenes (Scott et al., 1988). From these data it was concluded that decamethyl[5]pericyclyne should be classed as a homoaromatic molecule. As already discussed for the triquinacene series, the species used as non-homoaromatic models (and the calculated compensations for strain energies) may be inappropriate and thus this conclusion should be treated with some caution. Using our probes for homoaromaticity we were not able to obtain any evidence in support of the homoaromaticity of [129] (Williams and Kurtz, unpublished results). 

Quantum mechanical calculations have had support from the electron transmission spectroscopy of Giordan and co-workers.236 This technique measures the attachment energy for the formation of... 

Table 8. Vertical Electron Affinities (eV) of Some Alkynes as Determined by Electron Transmission Spectroscopy l46,1471...

We can get a good estimate of the absolute energies of molecular orbitals from photoelectron spectroscopy and electron transmission spectroscopy (see Chapter 2). Such experiments suggest energies for the HOMO and LUMO of butadiene to be -9.03 and +0.62 eV. respectively, whilst for ethene they are -10.51 and +1.78 eV, respectively. 

Electron transmission spectroscopy results bB3LYP/D95V+(D) except for G which is estimated from trends CDFT (B3LYP/6-311+G(2df,p)) destimated from stable valence anion complexes, e.g.., U(Ar)- ebest estimates from DFT basis set dependence study (vide infra). Thymine from ref. [88], note these values are likely too positive by 0.15 eV fEstimate of keto tautomer from enol tautomer experimental value (—0.46eV) plus calculated difference in energy between keto and enol tautomers (0.28 eV) ref. [94],... 

Photoelectron spectroscopy (PES) Q, and more recently electron transmission spectroscopy (ETS) (3, 4) have provided much information on the cation and anion states, respectively, of many hydrocarbons. Within the context of the Koopmans Theorem (KT) approximation, the cation states can often be associated with the filled orbitals and the anion states with the unfilled orbitals of a molecule. In this sense these two methods are complementary. However there are important distinctions between these two spectroscopic methods which arise in part from the very different lifetimes of the anions and cations. 

Electron transmission spectroscopy can provide information which is not readily available or accessible by other techniques. Here we will give just a few illustrative examples. A more complete discussion of the applications of ETS can be found in a recent review (4). 

In this paper we have tried to give the reader a general overview of the types of chemical information that can be obtained from electron transmission spectroscopy. ETS appears to be ideally suited for studying temporary anions formed by the cap-... 

The temporary anions associated with low-lyin unfilled orbitals generally have lifetimes in the range of 10 - 10 s in the gas phase. This paper discusses the use of electron transmission spectroscopy (ETS) to provide information on these short-lived anions. The sensitivity of the lifetimes to changes in symmetry is illustrated by comparing the electron transmission of benzene and various alkyl substituted benzenes. 

The radical anions have been likewise characterized by methods ranging from the various electrochemical techniques supplemented by EPR/ENDOR measurements to electron transmission spectroscopy. Radical anions can be conveniently generated in a matrix by Co y irradiation, e.g. in CD3OD, or in the liquid phase by potassium metal reduction in solvents such as hexamethylphosphoric triamide or dimethoxyethane. These ions have the n structure expected from calculations [14, 15, 25, 26]. 

A vertical electron affinity of -3.40 eV has been obtained for COClj, using electron transmission spectroscopy electron capture into a C-Cl cr-antibonding orbital was proposed [372a]. 

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