Photoelectron spectrum, of benzene

Figure 8.12 The He I ultraviolet photoelectron spectrum of benzene. (Reproduced from Karlsson, L., Mattsson, L., Jadmy, R., Bergmark, T. and Siegbahn, K., Physica Scripta, 14, 230, 1976)...

The resolution of the ZEKE-PE spectrum of 1,4-difluorobenzene can be compared with, for example, that of the ultraviolet photoelectron spectrum of benzene in Figure 8.12. The greatly increased resolution in the ZEKE-PE spectrum is attributable mostly to the fact that only photoelectrons with zero kinetic energy are being detected. It is also partly attributable to the molecules being in a supersonic jet this has the effect of sharpening the bands because of the restricted rotational populations in the ground state of the molecule. 

Figure 18.4 Rotationally resolved ZEKE photoelectron spectrum of benzene. Adapted from Muller-Dethlefs et al, Angew. Chem. Int. Ed., 1998, 37 1346, with permission of John Wiley Sons Ltd...

The benzene radical cation (Bz+) represents a prototype organic radical cation and has been studied extensively in the literature, both theoretically and experimentally. We mention early and more recent studies of its electronic structure,the photoelectron spectrum of benzene, including its vibrational structure and the high-resolution... 

Fig. 10. Comparison of theoretical (panels (a,b)) and experimental (j nel (c)) first bands of the photoelectron spectrum of benzene. The final state is the X Eig ground state of the cation. The JT activity of the modes i/i6, 1 17 and i/is is displayed by panel (a), the excitation of the symmetric CC-stretching mode 1/2 is included in panel (b). The...

Figure 4 (a) Calculated and (b) experimental photoelectron spectrum of benzene, reflecting the vibronic structure of the electronic... 

Smalley et al. /5/ found considerable auto-ionization in their threshold ionization spectrum of benzene exhibiting unexpected positions of several of the peaks. Conversely Reilly et al. /6/ showed from photoelectron spectra that the features observed could be well understood as vibrational energy levels split by Jahn-Teller forces acting upon the degenerate electronic state of the benzene ion. This paper repeats the two-color ionization experiment on benzene under optimized conditions and provides a rather complete interpretation of the observed ion spectrum. 

The absorption spectrum of 7 in aqueous acidic solutions has also been detected. The vertical gas-phase ionization potential /p of benzene was measured from the He(I) photoelectron spectrum as 9.23 ev.37e standard anodic peak potential Ep could not be measured directly but was estimated from data for alkyl-substituted benzenes as 2.86 V vs NHE. Jahn-Teller distortion in 7 has been reviewed, and the high-resolution state-to-state threshold photoionization spectrum of benzene gives the shape of 7 8 and diminished significantly the mystery regarding the structure. The geometries, hyperfine structure, and relative stabilities of the two mono-deuterated Jahn—Teller-distorted ions CeHsD were examined theoretically and experimentally. EPR and ENDOR studies showed the toluene radical cation possessed the B2g structure. The IR spectra of the two Jahn—Teller forms of 7 were also calculated. On the basis of the calculated energy levels, both 7 and 8 have been classified as antiaromatic. ... 

Fig. 11-28 An x-ray photoelectron spectrum of ANi and diamino-benzene-sulfonic acid (DABSA). The film was grown (13 cycles) from 0.163 M ANi + 0.0185 M DABSA in 1 M HCl at a scan rate of 50 mVs". After Reference [257], reproduced with permission.

Other studies, such as infrared and Raman spectra of gaseous benzene, neutron diffraction studies of crystalline benzene, and electron diffraction and microwave spectral studies, are equally incapable, according to critical analysis [87AG(E)782], of resolving unanimously the Dih—Deh structural dilemma of the benzene molecule. Furthermore, no decisive conclusion could be drawn from photoelectron spectra or H—NMR spectrum measurements of benzene molecules in a liquid crystal environment. The latter experiments merely indicate that the average lifetime of a Dih structure (if it appears on the PES) is less than 10 4 sec corresponding to the energy barrier of the Dih- >D6h-+D h interconversion of approximately 12 kcal/mol. 

The stabilization of a silicon-containing arene has not as yet been achieved. Nevertheless, silabenzene (7), 1-silatoluene (8) and hexamethyl-l,4-disilabenzene (9) have all been generated as transients.42"47 Both silabenzene and 1-silatoluene are stable when condensed in argon matrices. The UV spectrum exhibits three bands at 212, 272 and 320 nm expected for a jr-perturbed benzene. In its photoelectron spectrum, the lowest ionization energies are at 8.0, 9.3 and 11.3 eV (cfcalculated values derived by SCF methods of 8.2, 9.2 and 11.5 eV).48... 

Figure 14 demonstrates a photoelectron spectrum (top) for benzene [19] compared with a current ZEKE spectrum (bottom) of some 0.2 cm-1 resolution [20], even demonstrating the expected splitting of the v vibration due... 

Figure 14. Benzene spectra (a) photoelectron spectrum (b) ZEKE spectrum of a single band in (a).

Silabenzene (159) results from the flash pyrolysis of the silacyclohexadiene (158) and can be trapped in the argon matrix at 10 K (80AG(E)51, 80AGphotoelectron spectrum at 8.0 and 9.3 eV corresponding closely to those found for stibabenzene and for silatoluene (Scheme 248) (80JA429). 

From photoelectron spectroscopic studies it is apparent that a second ionization channel starts at 11.4eV in the case of benzene, i.e., at about 2.15 eV above the first ionization potential.219 The tail of the calculated spectrum will, therefore, be buried beneath the second ionization threshold. The second ionization threshold is indicated on Figure 30 by an arrow. Finally, there have been recent suggestions that there are two a ionization potentials, at 10.35 and 10.85 eV.220 If correct, excitation of these a-electrons would also lead to absorption intensity obscuring the contribution of transitions of the elg orbitals. 

Figure 27-10 Photoelectron spectra of ethene, ethyne, and benzene induced by 58.4-nm radiation from a helium-discharge lamp. For ethyne, the left part of the spectrum is shown with three different sensitivity levels. The horizontal scale here is in units of electron volts (eV), which can be converted to kcal mole-1 by multiplying by 23.06. (Published by permission of A. D. Baker and D. W. Turner, and of Accounts of Chemical Research.)...

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