Continuum absorption

Spectra of a spent bauxite-based desulfurization catalyst pellet ( 7 x 13 mm, examined in air) are shown in Fig. 9. The outside of the pellet was black and the single-beam spectrum S showed some of the continuum absorption found with chars. The compensated spectrum S/So, however, showed appreciable spectral structure. The broad band near 750 cm is probably due to the bauxite, and the absorptions near 3000, 1320 and 1000 cm-- - to a mixture of hydrocarbons and thio species formed during the reaction. The feature near 1640 cm l is probably caused by an olefinnic species. 

Wiscombe and Welch, 1986). Cloud absorption is related to droplet size in a complex way (Stephens and Tsay, 1990) so that errors in droplet size measurements can alter the model-predicted absorption by a cloud. The treatment of absorption due to water vapor is another possibility. As discussed by Crisp (1997), the treatment of water vapor in models is simplified and may not properly reflect, for example, continuum absorptions between major bands in the near-IR. Model calculations suggest that the presence of a thin, saturated layer of water vapor above the clouds, for example, leads to increased absorption by 2-6% (Davies et al., 1984 Podgorny et al., 1998). However, the Crisp calculations indicate that this cannot account for all of the observed excess absorption. 

The property of a molecule which gives the most information about the electronic continuum states is the differential oscillator strength in the continuum absorption region, which is defined by... 

As a rule, an excited diatomic molecule can be deactivated only through luminescence or dissociation, in the absence of collisions. Dissociative states show up in the absorption spectra as continuum absorptions, devoid of the sharp spectral lines characteristic of transitions between associative states. 

Although the oscillator strengths are dimensionless, their derivatives with respect to E are not, and units become a significant problem in continuum absorption. In cgs (electrostatic) units, equation (II.8) reads21... 

In our sensor, the interfering gas is water vapor. Water vapor does not have strong absorption bands in the 4.27 ym region, but it does have a relatively strong continuum absorption and a few scattered lines. The variations in water vapor in the open... 

Despite the many theoretical predictions of inelastic resonances (mainly observed in calculations with reduced dimensionality Manz 1989, for example) we do not know of an unambiguous experimental observation of resonances in atom-molecule or molecule-molecule gas-phase collisions. In contrast to full atom-molecule collisions pronounced resonance-like structures are actually rather common features in bound-continuum absorption spectra (Robin 1974, 1975, 1985 Okabe 1978 Fano and Rao 1986). In fact, all sharp structures in UV absorption spectra can be considered as resonances and therefore photodissociation provides ideal opportunities to investigate resonance phenomena, such as the lifetime, the decay mechanism, and the final state distributions of the fragments, on a very detailed basis. 

Region of absorption, A. Continuum absorption Wavelength of maximum Absorption absorption, coefficient, A. atm.-1 cm.-1 Remark... 

In the lower mesosphere and upper stratosphere, the continuum absorption of water vapor occurs in the domain of the O2 Schumann Runge bands. The photolysis frequency at zero optical depth varies from 4.0 to 6.5 x 10-6s-1 depending on the level of solar activity. 

One method which leads to a simple treatment of the penetration of radiation in the Schumann Runge bands and the photolysis rate of O2 involves establishing an equivalent cross section of O2 in the interval 5Ai and then applying the methods for continuum absorption. Thus, for each interval over which the quantum yield is assumed to be unity and the ozone transmission Trjo3 is not varying significantly with wavelength, the O2 photolysis frequency... 

Frederick, J.E., and J.E. Mentall, Solar irradiance in the stratosphere Implication for the Herzberg continuum absorption of O2. Geophys Res Lett 9, 461, 1982. 

For a pure autoionising resonance embedded in a single continuum, absorption by the underlying continuum is cancelled out at one energy close to the resonance energy, and the resulting transparency is referred to as a transmission window. 

In the XANES data analysis the first step is to remove the continuum absorption background due to transitions from levels of lower binding energy. This procedure is generally called pre-edge background subtraction. The relative absorption aCEj/a is usually plotted, where is the smooth atomic absorption above threshold determined by the usual EXAFS analysis. Fig. 2 shows two typical XANES spectra where the XANES are normalized to the atomic absorption. 

X-ray absorption of lanthanide 2p core levels probes the unoccupied atomic-like 5d states. Hence the occurrence of such intense absorption lines at the Lu,n thresholds. By comparison, the spectral shapes of the L and Lj lines are found to be nearly identical. The L amplitudes (normalized to the continuum absorption), however, systematically turn out to be up to 50% larger in R2O3 and RF3 (Feldhaus 1982, Wong et af 1984, Okusawa et af 1978) and to be about 5% smaller in the metals (Materlik et al. 1983a) than the corresponding L,n amplitudes. The slightly different Ljj, Li,i transition matrix elements cannot account for the observed strong discrepancies. Most likely the L, /L,n amplitude ratio reproduces different final-state... 

It is useful to treat the atomic absorption below the ionization (discrete line spectrum) and the continuum absorption above the ionization threshold separately. The arctan expression in eq. (1), experimentally confirmed through the K spectra, is a good approximation for the continuum absorption. The atomic absorption lines may be interpreted through optical multiplets using the Z + 1 approximation. The validity of this approximation has been successfully demonstrated in numerous cases of K and L spectra, first by Parrat (1939) in the K absorption of gaseous Ar. Here the optically determined wp Rydberg series ( > 4) of K (Z = 19 Z + 1 ) nicely fits the atomic absorption lines of 2s - 4p (K) X-ray excitation of Ar ( Z ). The Z -I-1 potential accounts for the creation of the deep core hole. The inflection point of the arctan shaped continuum absorption is located at the series limit, i.e. the first ionization potential. 

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