Photoionization Studies

Yang S and Knickelbein M B 1990 Photoionization studies of transition metal clusters ionization potentials for Fe... 

Koretsky G M and Knickelbein M B 1997 Photoionization studies of manganese oiusters ionization potentiais for Mn-,to Mn, J. Chem. Phys. 106 9810... 

On the other hand, the formation of ethylene was ascribed mainly to the unimolecular decomposition of a neutral excited propane molecule. These interpretations were later confirmed (4) by examining the effect of an applied electrical field on the neutral products in the radiolysis of propane. The yields of those products which were originally ascribed to ion-molecule reactions remained unchanged when the field strength was increased in the saturation current region while the yields of hydrocarbon products, which were ascribed to the decomposition of neutral excited propane molecules, increased several fold because of increased excitation by electron impact. In various recent radiolysis 14,17,18,34) and photoionization studies 26) of hydrocarbons, the origins of products from ion-molecule reactions or neutral excited molecule decompositions have been determined using the applied field technique. However, because of recent advances in vacuum ultraviolet photolysis and ion-molecule reaction kinetics, the technique used in the above studies has become somewhat superfluous. 

A possible role for shape resonances has been postulated in a number of the photoionization studies mentioned above [52, 53, 57, 60], although it has to be noted that except for camphor [57], the evidence for the existence of the shape resonance is not definitive. (It also then remains an open question how any such resonances, inferred from fixed geometry calculations, would manifest themselves in practice in large, and sometimes floppy, molecules, such as these chiral species.)... 

Additional details on some of these methods are described in other sections of this review. Attempts have also been made to determine excited-state populations in single-source mass-spectrometric experiments from an analysis of ionization efficiency curves.38ad There are several difficulties in applying such methods. For instance, it is now known from photoionization studies that ionization processes may be dominated by autoionization. Therefore, the onset of a new excited state is not necessarily characterized by an increased slope in the electron-impact ionization-efficiency curve, which is proportional to the probability of producing that state, as had been assumed earlier. Another problem arises because of the different radiative lifetimes that are characteristic of various excited ionic states (see Section I.A.4). 

P.W. Langhoff, Stieltjes-Tchebycheff moment-theory approach to molecular photoionization studies, in T. Rescigno, V. McKoy, B. Schneider (Eds.), Electron-Molecule and Photon-Molecule Collisions, Plenum, New York, 1979 A.U. Hazi, Stieltjes-moment-theory technique for calculating resonance widths, in T. Rescigno, V. McKoy, B. Schneider (Eds.), Electron-Molecule and Photon-Molecule Collisions, Plenum, New York, 1979. 

An alternative simple modeling of doped fullerenes, specifically, A C6o, was developed initially in [34]. It was then used extensively in a number of photoionization studies of thus encaged atoms [34 41], The method is based on approximating the C60 cage by a spherical potential V(r) which differs from zero only within an infinitesimally thin wall of a sphere of radius RC/ the latter being considered the C60 radius, Rc = 6.639 au [47] ... 

The previous formulation for the photoionization process provides the starting point for theoretical calculations. For simplicity, and because the conditions are well fulfilled, in many applications the dipole approximation is often used. (For extensions and derivations, relevant in the present context of photoionization studies with synchrotron radiation, see [KJG95] and references therein.) This approximation is based on a special property of the matrix element ... 

ESc96] Eland JHD and Schmidt V 1996 Coincidence measurements on ions and electrons, in VUV and soft X-ray photoionization studies, eds. U Becker and DA Shirley (Plenum, New York). [Fan35] Fano U 1935 Nuovo dm. 12 154. 

M. Litorja et al., A photoionization study of the hydroperoxyl radical, H02, and hydrogen peroxide, H202. J. Electron Spectrosc. 97, 131-146 (1998)... 

Extensive photoionization studies by Ding et al. (1987) have shown that there are essentially three different mechanisms responsible for the ionization of neutral heteroclusters of the type R Xm (where R = rare gas atoms and X = polyatomic molecule). Similar ionization mechanisms are also possible using electron-induced ionization studies. The various possibilities are summarized, as follows. 

The upper limit for the adiabatic first IE of GeH2 has been obtained by means of photoionization mass spectrometry in the course of photoionization studies of GcH molecules, generated by abstraction of hydrogen atoms from GeH4 by fluorine atoms302. It was found to be 9.25 eV302. On the basis of simple MO considerations it can be concluded that this ionization comes from HOMO, which is of the germanium atom lone-pair character. This is the only study of molecules of this simplest type. 

Photoionization study from Reference 116, see also Reference 117. 

The fluorine ion donor ability of Xep4 has been shown to be less than that of Xep2 and XeFe XeFg > Xep2 Xep4. These findings are in agreement with the enthalpies of ionization derived from photoionization studies (equations 9-11). 

A wide range of values exists for physical measurements of the ionization potential of ReFg. McDiarmid gives [16] 7.99 eV, Ellis finds [l7] 10.7 eV, Brundle and Jones are quoted [18] as finding 11.15 eV and Bloor and Sherrod [18] estimate 11.88 eV. A photoionization study by Vovna et al. [19] yielded 11.1... 

Photoionization studies of rare gas dimers have been carried out . Photoionization efficiency curves for the vdW molecules (Ar. .. Ar, Kr. .. Kr, Xe. .. Xe) were obtained by means of molecular beam techniques. The dissociation energies of the ions were calculated from the measured first ionization potentials (Table 6) and the dissociation energies of the parent vdW molecules. As the dissociation energy of vdW molecules is neghgible compared the dissociation energy of the rresponding cations, the latter energies (available from other sources) can be used to estimate first ionization potentials of vdW systems which have not yet been studied (values in parentheses in Table 6). 

Koretsky GM, Kerns KP, Nieman GC, Knickelbein MB, Rdey SJ (1999) Reactivity and photoionization studies of bimetallic cobalt-manganese clusters. J Phys Chem A 103 1997... 

Table 12. Enthalpies of Ionization of the Xenon Fluorides as Derived From Photoionization Studies 14)...

Binding energies and momentum distributions for electrons in the valence orbitals of CH4 have been presented 104 these are the first data obtained by the (e, 2e) reaction (electron-impact ionization with complete determination of the kinematics of the incident and emitted electrons) for a polyatomic molecule. The vertical I.P. s obtained for the lt2 and 2ai electrons of CH4 are compared with values from u.p.s. and photoionization studies in Table 6 the data derived from the three techniques are in satisfactory agreement. 

In a photoionization study of the I.P. and fragment appearance potentials of CHnCU-n (0=s n 3) and CBr4, it has been observed that although CBrJ is stable, CCU is unstable.105 In the energy range studied, fragmentation of the molecules was found to be limited to halogen loss. The experimental data... 

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