| Summary: | Dipole (e,e) spectroscopy has been used to determine absolute photo-absorption oscillator
strengths (cross-sections) for the discrete and continuum electronic transitions of CH₃F,
CH₃CI, CH₃Br, CH₃I, and BrCN. These data have been obtained at low resolution (1 eV
fwhm), spanning the visible to soft X-ray equivalent photon energy regions (4.5 to 450 eV),
and at high resolution (0.05 to 0.15 eV fwhm), in the valence and inner shell (Br 3d; I 4d;
C Is (BrCN); N Is) regions. The absolute photoabsorption oscillator strength scales were
established using either the Thomas-Reiche-Kuhn sum-rule (S(0)) or an S(-2)-based sum-rule
normalization technique.
To confirm the global accuracy of the dipole (e,e) photoabsorption oscillator strength
data, an assessment of the absolute scales of previously published dipole (e,e) photoabsorption
spectra 51 atoms and small molecules is made by deriving static dipole polarizabilities
using the S(-2) sum-rule. Alternative methods of absolute scale determination for photoabsorption
spectra using S(-2)-based normalization with dipole polarizabilities are also considered.
Various dipole oscillator strength sums S(u) (u=-l to -10) and L(u) (u= -1 to -6)
are evaluated using the previously published, and presently reported, dipole (e,e) measure-ments.
It is also shown that normal Verdet constants and values of the rotationally averaged
C₆ (A,B) dispersion coefficients can be reliably obtained either directly from the measured
oscillator strength spectra or from approximations which require only values of the dipole
sums S(u) and L(u) reported here.
Quantitative aspects of the molecular and dissociative photoionization are reported in he
valence shells of CH₃F and CH₃C1, and the valence shells and low energy inner shells (Br 3d
and I 4d) of CH₃Br, CH₃I and BrCN, have been studied using dipole (e,e-t-ion) spectroscopy.
Time-of-flight mass spectroscopy was used to determine the absolute partial oscillator str- engths for the molecular and dissociative photoionization channels of the methyl halides and
BrCN. In other work synchrotron radiation photoelectron spectroscopy measurements made
by Dr. Cooper, Dr. Chan and Dr. Tan were used to determine the absolute partial photoionization
oscillator strengths for the production of the electronic states of CH₃F+ , CH₃C1+
and CH₃Br+ . These measurements together were used to provide detailed quantitative in-formation
on the dipole-induced breakdown pathways of the methyl halides and BrCN under
the influence of VUV and soft X-ray radiation.
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