Ionisation of atoms

During the temperature rise in protostar formation, molecular dissociation occurs followed by ionisation of atoms. Assume that molecules and atoms are in thermal equilibrium with the protostar ... 

Kara, V., Paludan, K., Moxom, J., Ashley, P. and Laricchia, G. (1997b). Positron impact ionisation of atoms. Nuc. Inst. Meth. B 143 94-99. 

Shah, M.B., Elliot, D.S. and Gilbody, H.B. (1987). Pulsed crossed-beam study of the ionisation of atomic hydrogen by electron impact. J. Phys. B At. Mol. Phys. 20 3501-3514. 

In principle X-rays, as well as electron and gamma rays, can be used the main effect of gamma and X-rays is Compton scattering, i.e. ionisation of atoms giving rise to "primary electrons" these electrons, like those generated in an accelerator, lead to a number of other "secondary electrons" and ions. This cascade of secondary electrons (about 4000 to 6000 ionisations per initial secondary electron) loses energy in ionising the foodstuff molecules, with consequent production of free radicals and, thereby, of "radiolytic products" (Chapter 1). 

An analogy has therefore been drawn between multiple ionisation of atoms and Coulomb explosions of molecules in a laser field (see sec-... 

Quantum theory states that orbiting electrons of an atom must occupy discrete energy levels in order to be stable. Bombardment with ions of sufficient energy (usually megaelectronvolt protons) produced by an ion accelerator will cause inner-shell ionisation of atoms in a specimen. Outer-shell electrons drop down to replace inner shell vacancies, however only certain transitions are allowed. X-rays of a characteristic energy of the element are emitted. An energy dispersive detector is used to record and measure these X-rays. Only elements heavier than fluorine can be detected. 

Simultaneous measurements of the abundance of two (or more) isotopes of the same element in biogenic materials are usually obtained by mass spectrometry. This technique requires ionisation of atoms from the sample ions can he either positively or negatively charged, and they can be produced in a number of different ways ... 

When the plasma is sufficiently energetic, atoms may be ionised. The degree of ionisation depends on the temperature of the plasma and the ionisation energy of the considered element. In particular, for easily ionisable species, ionic spectra also contribute to the emission spectra observed in a plasma to a great extent The ionisation of atoms o of a particular element into ions i with liberation of electrons e is an equilibrium reaction. 

The excitation of electrons and the ionisation of atoms (which does not produce permanent damage in metals). 

The mass action law or Saha equation for thermal ionisation of seed atoms is... 

Ionisation. Ionisation of the ground-state gaseous atoms within a flame... 

The other example of an equation in Table 4.1 which includes a free electron is Example 10, which shows the process of ionisation of a sodium atom ... 

Both emission and absorption spectra are affected in a complex way by variations in atomisation temperature. The means of excitation contributes to the complexity of the spectra. Thermal excitation by flames (1500-3000 K) only results in a limited number of lines and simple spectra. Higher temperatures increase the total atom population of the flame, and thus the sensitivity. With certain elements, however, the increase in atom population is more than offset by the loss of atoms as a result of ionisation. Temperature also determines the relative number of excited and unexcited atoms in a source. The number of unexcited atoms in a typical flame exceeds the number of excited ones by a factor of 103 to 1010 or more. At higher temperatures (up to 10 000 K), in plasmas and electrical discharges, more complex spectra result, owing to the excitation to more and higher levels, and contributions of ionised species. On the other hand, atomic absorption and atomic fluorescence spectrometry, which require excitation by absorption of UV/VIS radiation, mainly involve resonance transitions, and result in very simple spectra. 

In terms of atomic spectrometry, NAA is a method combining excitation by nuclear reaction with delayed de-excitation of the radioactive atoms produced by emission of ionising radiation (fi, y, X-ray). Measurement of delayed particles or radiations from the decay of a radioactive product of a neutron-induced nuclear reaction is known as simple or delayed-gamma NAA, and may be purely instrumental (INAA). The y-ray energies are characteristic of specific indicator radionuclides, and their intensities are proportional to the amounts of the various target nuclides in the sample. NAA can thus... 

Figure 2.2. An energy level diagram illustrating photo-ionisation of an atom by removal of a K-shell electron. The Fermi level represents zero of the binding energy and the vacuum level represents zero...

A common method of calculating the approximate photo-ionisation cross-sections is to use the Gelius intensity model [79]. Here the cross-section for a particular orbital, , is expressed in terms of atomic contributions based on population analysis. 

This is a similar value to the temperature of the Sun derived optically or from A.max in the black body spectrum. In a colder star the Balmer series is weaker still, but in a hotter star the Balmer series lines are stronger. In very hot stars the Balmer series may become weaker again due to collisional ionisation of H atoms, removing the electrons from the atoms completely. 

When partial hydrolysis occurs as in Scheme 7.8 to form the 2-chloro-4-hydroxy species (7.5), the dye does not have a further chance to achieve fixation via the remaining chlorine atom. Under the alkaline conditions of fixation, ionisation of the acidic 4-hydroxy substituent leads to a massive feedback of electronegativity into the triazine ring, causing total deactivation of the remaining 2-chloro substituent. The remaining chlorine atom in... 

The gaseous component is made up of a mixture of atoms and molecules which may be either ionised or electrically neutral. Despite its modest proportions, the dust component plays a determining role in the thermodynamics and chemistry of the interstellar medium and in the star formation process that subsequently governs the whole evolution of the Galaxy. 

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