Transmittance spectrum integral

Fig. 1. The integral transient transmittance spectrum of pyrazine, calculated for a...

Fig. 2. Decomposition of the integral transient transmittance spectrum into the stimulated-Raman (a) and stimulated-emission (b) contributions.

Thus, the area under the spectrum would be a better measure of the overall efficiency of the extraction procedure than the absorbance at a single wavelength. The area was integrated by the trapezoidal area rule over the wavelength range 210-280 nm. This integration avoided the low transmittance at wavelengths below 200 nm. 

The solution of equations (4.69a,b) is complex since the absorption spectrum exhibits structure characterizing the numerous rotation and vibration-rotation lines of atmospheric molecules. The absorption coefficient or the transmission function Tr i, varies therefore considerably over small regions of frequency (or wavenumber) and in principle a line-by-line integration is required. Figure 4.22 shows, for example, the vertical transmittance through the atmosphere at the edge of the strong 15 pm CO2 bands (Edwards, 1992). 

In order to determine the spectrum transmittance H(ja)), it is necessary to calculate the integrals on the right-hand side of Eq. (2.85). According to the Euler formula ... 

Spectral hemispherical transmittance of samples is measured using a Perkin-Elmer Lambda-9 dual-beam UV-VIS-NIR spectrophotometer with an integrating-sphere attachment. Use of such a device allows the absolute transmittance to be measured as po- ASTM E903. Such spectral measurements can then be eonvolved with an appropriate standard terrestrial spectrum (as specified by ASTM G173) to compute a solar-weighted hemispherical transmittance, T2 (>.=200 nm to 2600 nm), as a meaningful single measure of optical performance. 

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