Computer Science
Scientific paper
Oct 1959
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1959natur.184.1223p&link_type=abstract
Nature, Volume 184, Issue 4694, pp. 1223 (1959).
Computer Science
Scientific paper
THE quantum efficiency of photo-decomposition in rigid solvents at liquid nitrogen temperature is for many substances quite low, and it is customary to expose the photolyte directly to the concentrated beam from a mercury lamp to produce sufficient photo-product for the measurement of its absorption spectrum. When measuring the quantum efficiency, it is difficult to produce a sufficiently high intensity of monochromatic light at a series of wave-lengths and covering the whole area of the reaction cell. A further difficulty is the absorption of the irradiating light by the products of the reaction. This can produce a large inner filter error if comparatively high concentrations are photolysed to a significant degree. With thionine in E.P.A. glass the quantum efficiency is less than 0.005 and to avoid these difficulties the application of spectrofluorimetry was investigated. As an analytical technique, spectrofluorimetry is much more sensitive than absorption spectroscopy1 and allows the use of dilute solutions, so that a comparatively small proportion of the photolysing light is absorbed. A further advantage is that light from a monochromator can be focused on a small area of the reaction cell so that much higher intensities can be obtained than if the whole cell face were illuminated. After irradiation, comparison of the intensity of the red thionine fluorescence from the irradiated area with that from unirradiated areas on either side gives a direct measure of the proportion of dyestuff consumed. The spectrofluorimeter can also be used to observe the fluorescence emission and excitation spectra of fluorescent photo-products. At the concentrations used (< 10-5 M), complications due to energy transfer processes are negligible.
Parker Alexander C.
Rees W. T.
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