Intensities free-atom

In a number of cases, the temperature of the filament and thermodynamic parameters allow one to calculate [9] the flux intensity of free atoms produced in dissociation of molecules. Specifically, in the case of dissociation of hydrogen, oxygen, and nitrogen molecules on hot metal filaments under pressures of molecular gases higher than lO" Torr, the flux intensity of atoms A originating from A2 molecules is given by... 

For a weak CF the ground CFT is 5Eg and the first excited CFT lies at A0 = 10Dq. The electronic spectrum for the octahedral complex also contains a transition A to the 3 Tig term arising from the free-atom 3H term (this is spin forbidden and consequently of a weak intensity, Table 73 and Fig. 123). 

The formed free atoms absorb the light at a characteristic wavelength from a hollow cathode lamp that is positioned on one side of the flame. A spectrophotometer with a grating monochromator located on the other side of the flame measures the intensity of the light beam. Because absorption is proportional to the number of free atoms that are produced in the flame, the light energy absorbed by the flame is a measure of the element s concentration. The FLAA technique is relatively free of interelement spectral interferences, but it has the sensitivity that is inferior to ICP-AES or GFAA. 

Because the / orbitals are so well shielded from the surroundings of the ions, the various states arising from the / configurations are split by external fields only to the extent of 100 cm 1. Thus when electronic transitions, called/—/transitions, occur from one / state of an / configuration to another J state of this configuration the absorption bands are extremely sharp. They are similar to those for free atoms and are quite unlike the broad bands observed for the d—d transitions. Virtually all the absorption bands found in the visible and near-uv spectra of the lanthanide +3 ions have this linelike character. The intensities of the/—/bands show measurable sensitivity to the nature of the coordination sphere but the relationship is complex and not quantitatively understood. 

In calculating a theoretical photoelectron spectmm, the atomic ionization cross section a. is usually taken so far from the theoretical values calculated for a neutral free atom in the ground state. However, the MO calculation by DV-Xa method is carried out self consistently and provides Q. by Mulliken population analysis using the SCF MO wave function calculated. In the present calculations, the atomic orbital Xj used for the basis function flexibly expands or contracts according to reorganization of the charge density on the atom in molecule in the self-consistent field. Furthermore, excited state atomic orbitals are sometimes added to extend the basis set. In such a case, the estimation of peak intensity of the photoionization using the data of Oj previously published is not adequate. Thus a calculation of the photoionization cross section is required for the atomic orbital used in the SCF calculation in order... 

With development of solid-state detectors, relative x-ray intensities, such as, KP/Ka ratios, have been measured and compiled in the tabulated or graphical forms [2-4]. However, these values are still considered as an atomic property and compared with the theoretical calculations for free atoms [5]. This is because for calculation of x-ray emission rates in molecules it is necessary to perform multi-center integration for molecular wave function. Such calculations are tedious and require a lot of computation time and large memory capacity. 

For the case cited above, the ponderomotive energy is approximately 1 eV. For typical short pulse experiments today, this energy can easily be hundreds of electron volts. Therefore the wave function of a photoelectron in an intense laser field does not resemble that of the normal field-free Coulomb state, but is dressed by the field, becoming, in the absence of a binding potential, a Volkov state [5], This complex motion of the photoelectrons in the continuum is very difficult to reproduce in terms of the field-free atomic basis functions, so that we have chosen to define our electron wave functions on a finite difference grid. These numerical wave functions have the flexibility to represent both the bound and continuum states in the laser field accurately. 

The effect of atmospheric gas on the emission of an LIB plasma [146] exhibits selfabsorption in He compared to Ar as a result of increased free atom populations in the outer regions of the plasma. Spectral line widths do not correlate well with atmospheric gas. This rules out Doppler effects as a major source of broadening in the laser-induced plasma. The use of a low pressure (ca. 1 torr) to examine the influence of this variable on the shock wave or secondary plasma revealed an increased emission intensity, which confirmed the assumption that the secondary plasma was excited by the shock wave. 

If a beam of electrons falls on a free atom, the intensity of the beam scattered through an angle 0 is, at a distance r from the scattering atom,... 

I would first emphasize that the formula (1) is derived for free atoms. There are three reasons why the scattering factor may be different for atoms bound in a crystal. Firstly, there is a potential jump, usually of the order of 10 volts, at the crystal surface. This will cause a refraction of the electron beam. Secondly, the wave scattered from any atom may be scattered again by another atom. Neither of these disturbing factors will greatly affect the scattered intensity for electrons of energy above, say, 2000 volts. Thirdly, the atoms in the crystal may be deformed or ionized by the neighbouring atoms. This third cause will be discussed later. 

However, near the Earth s surface, the hydrocarbons, especially olefins and substituted aromatics, are attacked by the free atomic O, and with NO, produce more NO2. Thus, the balance of the reactions shown in the above reactions is upset so that O3 levels build up, particularly when the Sun s intensity is greatest at midday. The reactions with hydrocarbons are very complex and involve the formation of unstable intermediate free radicals that undergo a series of changes. Aldehydes are major products in these reactions. Formaldehyde and acrolein account for 50% and 5%, respectively, of the total aldehyde in urban atmospheres. Peroxyacetyl nitrate (CH3COONO2), often referred to as PAN, and its homologs, also arise in urban air, most likely from the reaction of the peroxyacyl radicals with NO2. 

It seemed at first surprising that isolated and rather intense atomic transitions should be present in the solid. In order to establish the correctness of this interpretation, it was necessary to investigate the spectra of the corresponding free atoms which, largely for technical reasons, had escaped observation until then. They were not in fact uncovered until 1974 [189, 190], when the first observations of a giant resonance in a free atom were reported independently. 

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