Ionization double

Figure Bl.10.11. Electron impact double ionization triple coincidence experiment. Shown are the source of electrons, target gas, tluee electron detectors, one for the scattered electron and one for each of the ejected...

Dupre C, Lahmam-Bennani A and Duguet A 1991 About some experimental aspeots of double and triple ooinoidenoe teohniques to study eleotron impaot double ionizing prooesses Meas. Sol. Technol. 2 327... 

When the states P1 and P2 are described as linear combinations of CSFs as introduced earlier ( Fi = Zk CiKK), these matrix elements can be expressed in terms of CSF-based matrix elements < K I eri IOl >. The fact that the electric dipole operator is a one-electron operator, in combination with the SC rules, guarantees that only states for which the dominant determinants differ by at most a single spin-orbital (i.e., those which are "singly excited") can be connected via electric dipole transitions through first order (i.e., in a one-photon transition to which the < Fi Ii eri F2 > matrix elements pertain). It is for this reason that light with energy adequate to ionize or excite deep core electrons in atoms or molecules usually causes such ionization or excitation rather than double ionization or excitation of valence-level electrons the latter are two-electron events. 

In case when the major input into the change of concentration of free carriers is provided by double-ionized oxygen vacancies which is valid at high temperatures the concentration of conductivity electrons is [e] w 2[Vq ], which, recalling expressions (1.121), (1.124) and (1.125) brings us to formula... 

FIGURE 4.4 Schematic of threshold behavior of ionization processes. Under ideal conditions, one expects a step function for photoionization, a linear variation with energy under electron impact, and a parabolic dependence for double ionization by electron impact. 

Evaluation problems The peak at atomic number 16 may, for example, be due to oxygen fragments resulting from Oj, HjO, COj and CO the peak at atomic number 28 from contributions by Nj as well as by CO and CO as a fragment of COj the peak at atomic number 20 could result from singly ionized Ne and double-ionized Ar. 

Figure 2 The photoabsorption (c), photoionization (o-,-), and photodissociation (cr

Double Ionization-Chamber Method (Real-Photon Method)... 

The double ionization-chamber method [19] provides an excellent means of measuring the photoabsorption cross sections of atoms and molecules in the range of the incident photon... 

Fig. 4 shows the illustration of a double ionization chamber. We describe the process of measuring the photoabsorption cross sections as follows, /q denotes the incident photon flux coming into the chamber filled with atoms or molecules of the number density n, I and I denote the photon fluxes entering and leaving plate 1, respectively, and I2 and I2 denote the photon fluxes entering and leaving plate 2, respectively. The ion currents q and q collected by plates 1 and 2, respectively, are expressed as... 

Figure 4 The outline of the double ionization chamber. (From Ref. [19].)...

In Fig. 7 [7], we compared the photoionization quantum yields (t/,) of CH4, C2H6, and C3H8, which were measured by our group using the double ionization chamber and synchrotron radiation, as described in Section 2.1. The photon energies are considered in two ranges, as follows, in terms of the behavior of the t/, curves as a function of the incident photon energy [7] ... 

Fig. 5 shows that the mean free path of low-energy carbon ions is less than that of a water molecular diameter. Calculations based on such short mean free paths may predict two energy loss events within the same molecule. However, as discussed elsewhere in this book, the double ionization cross section is much lower than predicted by these results. The problem is that cross sections are normally based on a single isolated collision at gaseous density. Extrapolation to the condensed phase can lead to unrealistic predictions. 

As mentioned previously, most ions are singly charged, but double ionization does occur and this is indicated by peaks at half-mass units. These represent odd-numbered masses that carry a double charge. For example, a doubly charged ion of mass 89 gives rise to a peak at 89/2 or m/z 44.5. 

The absorption of light increases as the concentration of interstitial zinc increases. Scharowski subtracts the intrinsic absorption, as found in relatively stoichiometric crystals, from the total absorption in a highly doped sample, and considers the excess absorption to arise from the double ionization of interstitial zinc. This excess absorption peaks at about 3.2 e.v., and from this Scharowski concludes that the energy of ionization of interstitial Zn+ is 3.2 e.v. The fact that this is equal to the forbidden gap width is considered to be coincidental. 

The oxygen ions, as drawn, have two acceptor traps, corresponding to the possibility of double ionization. The evidence for this double ionization of the adsorbed oxygen, presented in Section IV, is, however, inconclusive. 

To summarize the various results which suggest the energy level diagram of Fig. 1, many authors have shown (24,26,28) that zinc oxide has interstitial zinc as a donor impurity. As determined by conductivity and Hall effect measurements, the energy level for single ionization of this interstitial zinc is of the order of several hundredths of an electron volt below the conduction band when the concentration of donors is of the order of 10 cm. . The energy level for double ionization, from optical absorption measurements, appears to be at about 3.2 e.v. below the con-... 

Evidence has been presented (31,32) that oxygen is chemisorbed on the surface of zinc oxide. The energy level for the first electron is denoted by Es. From conductivity investigations, a second surface energy level, associated with adsorption, has been indicated with an energy level at about 0.8 e.v. below the conduction band at the surface. The hypothesis has been presented that this level is associated with double ionization of the adsorbed oxygen. 

Photoconductive response (the rate of creation, or the rise, of the photocurrent, and the rate of decay of the photocurrent) appears to be divided into fast and slow responses. The fast responses, with time constants for rise and decay of the order of a second or less, have been adequately interpreted by Mollwo, et al. (53-55), Weiss (56), and Heiland (47,57) as bulk processes. These authors have concluded that the fast response processes are associated with the double ionization of interstitial zinc, and have proposed that the photon excites electrons from the valence band, and that the hole immediately recombines with the electron from an interstitial Zn+, producing double-ionized zinc ions. 

L. Woste You showed that the above-threshold ionization process always ends at the bottom of the ionic state when exciting the system with femtosecond pulses. So, going to higher laser powers, you observe the consecutive onset of multiphotonic processes. What happens when you cross the double-ionization barrier Is the same true for doubly charged clusters ... 

Figure 16. Double-ionization oscillator strength of neon , (e-ion) data144 obtained using measured (2 + /1+) ratio and photoabsorption data due to Watson 146 solid curve, calculation by Chang and Poe.95...

Figure 31. Oscillator strength for dissociative ionization of N2 , From Wight et al. 25 broken curves, partial oscillator strengths for three dissociative ion states, with C state dissociative only from o = 3 up, which makes total C-state spectrum approximately 10% higher than spectrum shown here. The three broken curves combined equal total spectrum and give a best fit with other data points dissociative double ionization (N + + N+) is expected to set in at 48 eV o and A, from branching ratios measured in an electron-electron coincidence experiment.171 Chain curve (N2+) from El-Sherbini and Van der Wiel.108...

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