Coulomb ionization

On the other hand, fluorescence yields for the XI lines in the case of the ion impacts were assumed to be Yxi only for k L K L through the shake process. Here Yxi was determined from the photon induced X-ray spectra. However, for the K L state produced through the direct Coulomb interaction, Y=0.013 was adopted because the direct Coulomb ionization is not accompanied with the orbital reairangeinent. These considerations give the total X-ray production cross sections for the XO and XI lines, ctxo and Oxi,... 

The square of the molecular orbital coefficient for the K L" state is summarized in Table I. Also shown, in parentheses, is the energy (eV) relative to the energy of the highest occupied molecular orbital (HOMO). Here the orbital components are expressed as the sum of the squares of the partial expansion coefficients and of the overlap populations for the orbitals. From Table 1 it is easily seen that the K L X-ray line is mainly composed of three components each separated by leV. The observed X-ray satellite spectra for MgF and NiFj are shown in the solid lines in Figs. 8 and 9. Fig. 8 shows spectra induced by 2 MeV He impact, and Fig. 9 by 84 MeV impact. These excitation conditions produce mostly direct Coulomb ionization, not shake ionization. The observed spectra are now deconvoluted into K L" components. The rather broad K L line is further deconvoluted into three molecular orbital components each separated by... 

Typical photon induced X-ray spectra, emitted from NaF, KF, RbF and CsF, are shown in Fig.l3. The intensity distributions of these spectra can be explained by taking only the shake and ROR processes into account, because they are free from the satellite X-rays emitted through the direct Coulomb ionization. Then photon induced satellite spectra can be used, in the following manner, to estimate the ion-induced or particle induced X-ray satellite intensities without any complicated calculations. This is because the excitation process in particle induced X-ray emission (PIXE) can be described by a snperposition of the direct Coulomb, the shake and ROR processes. Here the shake and ROR processes are common to both photon- and particle- induced X-ray emission spectra, allowing utilization of the same ROR probability to explain both spectra. 

The ionization mechanism of X-rays induced by charged particles is of three kinds (1) Coulomb ionization (2) electron capture, and (3) electron Promotion. 

According to direct Coulomb ionization models (vahd for Z -C and > 2)) the ionization cross-section for a certain shell becomes maximum when the reduced energy E/ XU) is equal to unity. Here A is the mass of projectile in electron mass unit and U is the average binding energy of the shell. The direct Coulomb ionization phenomenon is described by the following approximations ... 

The technique introduced by the Macfarlane group was originally referred to as Coulomb ionization since the process of excitation was similar to the Coulomb excitation of nuclei by fast heavy ions. The term fission-fragment induced desorption (FFID) was used by Field and ChaiC to describe the technique without implying a particular mechanism. Other investigators, including Bo Sundqvist at the Tandem... 

The first part of paper will deal with the relation of Coulomb ionization to the molecular orbital (MO) picture of the united atom and the application of these results to the structure of K shell in super-heavy atomic systems. 

In asymmetric collisions the lowest orbital, the Isa, connects the Is orbital of 2 with the Is of Z. This is illustrated in Fig. 1 for the 35Br-i oZr system. When the system is sufficiently asymmetric the 2pa is far removed from Isa radial coupling between the two is weak and the only way to form a vacancy in the Is shell of the high Z collision partner is by Coulomb ionization from the Isa. Since Coulomb ionization cross sections are dependent on the electron binding energy, measurements of the impact parameter depen-... 

Were we to simply add the ionization energy of sodium (496 kJ/mol) and the electron affin ity of chlorine (—349 kJ/mol) we would conclude that the overall process is endothermic with AH° = +147 kJ/mol The energy liberated by adding an electron to chlorine is msuf ficient to override the energy required to remove an electron from sodium This analysis however fails to consider the force of attraction between the oppositely charged ions Na" and Cl which exceeds 500 kJ/mol and is more than sufficient to make the overall process exothermic Attractive forces between oppositely charged particles are termed electrostatic, or coulombic, attractions and are what we mean by an ionic bond between two atoms... 

In the derivation of the Boltzmann equation, it was noted that the distribution function must not change significantly in times of the order of a collision time, nor in distances of the order of the maximum range of the interparticle force. For the usual interatomic force laws (but not the Coulomb force, which is of importance in ionized gases), this distance is less than about 10 T cm the corresponding collision times, which are of the order of the force range divided by a characteristic particle velocity (of the order of 10 cm/sec for hydrogen at 300° C), is about 10 12 seconds. 

Fig. 10. Formation of the bipolaron (= diion) state in poly-p-phenylene upon reduction In the model it is assumed that the ionized states are stabilized by a local geometric distortion from a benzoid-like to a chinoid-Iike structure. Hereby one bipolaron should thermodynamically become more stable than two polarons despite the coulomb repulsion between two similar charges...

Section 3.3.4 pointed out that cosolvents alter aqueous ionization constants as the dielectric constant of the mixture decreases, acids appear to have higher pKa values and bases appear (to a lesser extent than acids) to have lower values. A lower dielectric constant implies that the force between charged species increases, according to Coulomb s law. The equilibrium reaction in Eq. (3.1) is shifted to the left in a decreased dielectric medium, which is the same as saying that pKa increases. Numerous studies indicate that the dielectric constant in the region of the polar head groups of phospholipids is 32, the same as the value of methanol. [381,446-453] Table 5.2 summarizes many of the results. 

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