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Smallwood, S. E. F. (1961) A comparison of some methods of measuring spectral intensities. Doctoral thesis, Northern Polytechnic.
Some methods of comparing the intensities of spectrum lines and of molecular bands are described using photographic plates, photomultipliers and thermopiles as the detecting devices. The design and construction of a photoelectric Eagle mounting grating spectrograph is also described, the linear spectrum and relatively high dispersion of this instrument making it attractive for such intensity measurements. measured. The performance of each of the detectors was assessed by using them, in turn, to determine the intensity ratios of the components of a particular mercury triplet. In some cases, the corresponding triplet in the cadmium spectrum was also measured. These particular triplets were selected because each component originated from a common S level, the emitted intensities should then have a constant ratio, whatever the excitation conditions.
In the case of molecular band spectra, much variability in the published intensity ratios of a given progression has been noticed. Some methods of comparing intensity of such molecular band spectra are described. An assessment of these methods was made by using them, in turn, to measure the intensity ratios of the components of two selected progressions in the nitrogen second positive band system, and of one progression in the carbon monoxide Angstrom system. These progressions had been selected as originating from a common upper level.
It is shown that the different methods of measurement give reasonably consistent results with an identical source, and that experimental error is unlikely to account for the differences found in the literature. It is concluded that variations of the operating conditions of the sources used are most probably responsible for the differences in the reported values.
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