Electron spectroscopy Penning

Figure 11. Schematic drawing of experimental setup used for Penning ionization electron spectroscopy using helium metastables.

Reaction of selenoxanthene 9 with bromine affords the selenium addition product 72 (Equation 26) however, selenoxanthone 10 reacts with bromine to form a molecular complex 73 (Equation 27). The explanation of this difference in reactivity is based on the differences in ionization potentials of selenium in these molecules which were determined using penning ionization electron spectroscopy <1998JOC8373>. These results are consistent with ab initio calculations of the electronic states of the precursors (see Section 7.11.2). 

Block et al.194 examined the effects of trimethylsilyl substitution on the first vertical ionization potentials by photoelectron and Penning ionization electron spectroscopy studies of a range of cyclic and noncyclic sulfides and ethers. It was shown that substitution of oxirane 218 with a trimethylsilyl substituent as in 219 lowered the ionization potential by 0.90 eV (20.8 kcal/mol), while similar substitution of dimethyl ether 220 in 221 lowered the ionization potential by 0.64 eV (14.8 kcal/mol). By comparison, the effects of silyl substitution on sulfur lone-pair ionization potentials was found to be smaller thus the ionization potential of dimethyl sulfide 222 is lowered by 0.37 eV upon trimethylsilyl substitution in 223, and the trimethylsilyl-substituted thiirane 225 is lowered by 0.59 eV relative to thiirane 224. The raising of the energy of the sulfur lone-pair electrons in the thiirane 225 is also apparent from its UV spectrum, where there is a bathochromic shift in the absorption maximum compared to the parent 224. 

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

Electron spectroscopic techniques are based on determination of the energy distribution of electrons released in the ionization process. Two of these techniques became very popular among chemists and molecular physicists, namely photo-clectron spectroscopy (PES) and X-ray electron spectroscopy also termed electron spectroscopy for chemical analysis (ESCA) Penning ionization electron spectroscopy (PIES) is related to PES, but the target molecule is ionized by electronically cxcital (metastable) atoms of a noble gas, mostly He, Ne and Ar instead of the photons used in PES. PIES is not sudi a widely used tedmique as PES and ESCA, but probably the most attractive one for vdW molecules. 

Electron spectroscopy can be divided Into several categories. These would Include X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA), Ultraviolet Photoelectron Spectroscopy (DPS) and Auger Electron Spectroscopy (AES). Other electron spectroscopies Include Penning Ionization and Ion neutralization. XPS uses soft X rays as the... 

Penning ionization electron spectroscopy (PIES), also referred to as metastable atom electron spectroscopy... 

INS is very similar to MIES (metastable impact electron spectroscopy) or PIES (penning ionisation electron spectroscopy) except that in INS ions are used instead of metastable atoms. 

Aaonyms PIES (Penning ionisation electron spectroscopy)... 

This chapter describes fundamental aspects of the electronic structure of organic semiconductors (small molecules and polymers), and their interfaces, and the method to bridge the electronic structure and electrical property more directly using ultraviolet photoemission spectroscopy (UPS). Penning ionization electron spectroscopy (PIES), which is the most surface-sensitive method, is also introduced for study of electronic states at outermost surfaces of solids, which are responsible for charge exchange through the interfaces between different materials when they get contact to form a hybrid system. 

Penning ioni2ation electron spectroscopy is also called (i) metastable atom electron spectroscopy (MAES), (ii) metastable deexdtation spectroscopy (MDS), (iii) metastable quenching spectroscopy (MQS), and (iv) metastable impact electron spectroscopy (MIES), where atom at metastable state is used instead of photon to ionize the target material When a slow, long-lived, electronically excited metastable atom hits a solid surface, most of its excitation energy is used to eject electrons from the surface. Unlike photons used for UPS, metastable atoms do not penetrate into the bulk of the solid. PIES, therefore, excites the outermost surface layer selectively (39). 

Cermak has also introduced a new method for the study of Penning and heteronuclear associative ionization of long-lived electronically excited atoms and molecules, which he has called Penning-ionization electron spectroscopy. Since Penning ionization usually predominates, the name is quite an appropriate one. Cermak has used the method to measure ionization potentials of some 40 molecules and the values obtained agree very well with those determined by photoelectron spectroscopy. The method has been further shown by Cermak and Herman, Fuchs and Niehaus, and Hotop and Niehaus to be of considerable value in mechanistic considerations of Penning and heteronuclear associa-... 

Metastable De-excitation Spectroscopy (MDS), also known as Penning Ionization Electron Spectroscopy (PIES) and Metastable Quenching Spectroscopy (MQS)... 

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