Absolute Oscillator Strengths

Absolute electron-impact cross sections have been measured by Chamberlain, et al.111 for excitation of the 2 P and 2 5 states of helium at a scattering angle of 5° in the energy range 50-400 eV (these conditions are far from the optical limit). Measurements of this type are extremely difficult but with care may approach an accuracy of 5 to 10%. Such determinations are useful for normalizing relative measurements. 

Total ionization oscillator strengths (see Section V) may be put on an absolute scale by normalizing to the total absorption at energies where the ionization efficiency (see Section II) is unity. For most species this is the case above 20 eV.25 102 Alternatively, absolute photoionization cross sections 122 may be used for normalization. 

A second method that exists for normalization of relative absorption curves is dependent on the Thomas-Reiche-Kuhn (TRK) sum rule (see Section II). The zeroth sum rule simply states that the total oscillator strength for photoabsorption is equal to the number of electrons in the atom or molecule. In cases where the electronic shells are well separated 

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Such determinations of the absolute oscillator strengths can be used to convert relative oscillator strengths obtained by other methods(2Z>15.>12 to absolute oscillator strengths. 

McLaren R, Clark SAC, Ishii I, Hitchcock AP (1987) Absolute oscillator strengths from -shell electron energy-loss spectra of the fluoroethenes and 1,3-perfluorobutadiene. Phys Rev A 36 1683-1701 Medlin JW, Shrrill AB, Chen JG, Barteau MA (2001) Experimental and theoretical probes of the structure of oxametalacycle intermediates derived from 1-epoxy-3-butene on Ag(110). J Phys Chem 105 3769-3775... 

The measured and calculated absolute oscillator strengths are given in the following table ... 

Taking as the only experimental parameter the CBC to CBB relation from phonon spectroscopy (53,204), the CBC, CBB and BDB concentration were calculated (Fig. 49). Subsequently the concentrations of B12 and BnC icosahedra (Fig. 50) immediately follow from the stoichiometry of the compound. The calculated BDB concentrations agree with the concentrations of B(3) vacancies determined by neutron diffraction. Compared with Fig. 26 (based on absolute oscillator strengths experimentally determined) the results in Fig. 49 and 50 (based on the quotient of oscillator strengths) show remarkable differences in the more boron-rich range only. The results in Figs. 49 and 50 are more reliable because in the quotient, systematic experimental error is largely eliminated (for details see (202)). 

Auzel et al. (1982) calculated the absolute oscillator strengths between J-manifolds of (5f ) in an aqueous hydrobromic solution and in ThBr4. The oscillator strengths... 

G. Cooper, T. Ibuki, and C. E. Brion, Absolute oscillator strengths for photoabsorption, photoionization and ionic photofragmentation of silane. I. The valence shell, Chemical Physics, vol. 140, no. 1, pp. 133—145, 1990. 

Branching ratios R have been measured for transitions from seven odd levels and absolute oscillator strengths f derived from these R values and from the radiative lifetimes T listed in Table 2/20, p. 188 [20]. They are given in Table 2/21, p. 189. 

R branching ratio f absolute oscillator strengths S most sensitive line s sensitive line. 

In Tables -A, we report oscillator strengths for some fine structure transitions in neutral fluorine, chlorine, bromine and iodine, respectively. Two sets of RQDO/-values are shown, those computed with the standard dipole length operator g(r) = r, and those where core-valence correlation has been explicitly introduced, Eq. (10). As comparative data, we have included in the tables /-values taken from critical compilations [15,18], results of length and velocity /-values by Ojha and Hibbert [17], who used large configuration expansions in the atomic structure code CIVS, and absolute transition probabilities measured through a gas-driven shock tube by Bengtson et al. converted... 

The absorption oscillator strength for CH4 was obtained24 from the forward scattering. The absolute ionization efficiency was then obtained by normalizing the quotient of the relative oscillator strength for ionization and absorption on a few absolute points obtained by a calibration procedure using a mixture of helium and neon. The ionization efficiency is unity from about 5 eV above threshold to the limit of the data at 80 eV. 

It is a usual practice to assume that the oscillator strengths of hypersensitive transitions are proportional to the Ti parameter. This assumption is reasonable for aqueous systems. In some hypersensitive transitions, Ui4) and I/<6) matrix elements are significant relative to the magnitude of U(2). Thus it is necessary to be careful when dealing with absolute values of oscillator strength alone, since symmetry may effect a significant contribution to the intensity of both hypersensitive and non-hypersensitive transitions. Caution should be... 

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