Spectroscopy electron-impact

CELS, EIS Characteristic-energy-loss spectroscopy, electron-impact spectroscopy [128] Same as EELS Same as EELS... 

A further technique exists for the determination of triplet energy levels. This technique, called electron impact spectroscopy, involves the use of inelastic scattering of low-energy electrons by collision with molecules. The inelastic collisions of the electrons with the molecules result in transfer of the electron energy to the molecule and the consequent excitation of the latter. Unlike electronic excitation by photons, excitation by electron impact is subject to no spin selection rule. Thus transitions that are spin and/or orbitally forbidden for photon excitation are totally allowed for electron impact excitation. 

Although a detailed treatment of the fundamental concepts of collisional processes is outside the scope of this text, it is hoped that the following discussion will suffice to give the reader an elementary understanding of what is occurring in electron impact spectroscopy. 

Eastman, R. H., 158, 166 Eaton, P. F., 460 Eigen, M., 80 Eisenberg, W., 125 Electrocyclic addition, 46 Electrocyclic reaction rules, 339 Electrocyclic reactions, 402,408 4n-examples, 408 (4n + 2)-examples, 410 Electron impact spectroscopy, triplet energy, 220-223 Electronic energy transfer, 267 Electronic integral, 21 Electronic transitions /-a ,16 n -Mr, 16... 

Low-energy electron impact spectroscopy of [l.l.l]propellane reveals an unusually low energy for electron capture to form the radical anion (2.04 eV compared to about 6 eV for most alkanes) ... 

In the case of lower impact energies in forward scattering and for ejected electron analyzers used in photoelectron as well as electron-impact spectroscopy, the larger changes in voltage ratios at the analyzer input result in transmission variations (with electron energy) that may not be readily corrected with zoom lenses (this is particularly true where slits are... 

Allan M (1989). Study of triplet states and short-lived negative ions by means of electron impact spectroscopy. J Electron Spectrosc Relat Phenom 48 219—351. 

The lower triplet state corresponds to the 3a (3a ) transition of the tt,x type. This band could underlie the 385-to 200-nm band since the Franck-Condon accessible region may be quite high in energy. Excited electronic states of ketene have been recently studied by electron impact spectroscopy (87). 

The reactivity of furan is most often associated with triplet states. Calculations (INDO) of charge distribution agree with reactivities actually found, and triplet cr-complexes are suggested as key intermediates.11 Low-lying triplet states have been detected in furan by variable-angle electron-impact spectroscopy (singlet -> triplet transitions are most intense at 3.99 and 5.22 6V).12 Excited stated may be quenched by furan without any indication ofexciplex formation.13... 

For a nonradiative lifetime of 10 13s, the linewidth will be 50 cm-1, causing the rotational structure to disappear and the band to become diffuse. For a shorter nonradiative lifetime, 10 15s, the vibrational structure disappears and the spectrum becomes similar to a continuous spectrum. As spectral lines become broader and broader, their intensity is spread out and becomes lost in the background. However, low-resolution techniques, such as photoelectron spectroscopy or electron impact spectroscopy, can enable detection of strongly predissociated bands (see Table 7.2). 

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