The Absorption Spectrum of Diacetylene in the Near Ultraviolet. II

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Abstract
The absorption spectrum of diacetylene has been reinvestigated with an instrument of higher dispersion. The bands in the region λλ2970–2650A are sharp and narrow, and very closely spaced. Two progressions with a frequency difference ∼690 cm—1 have been found. Those below λ2650A are very diffuse, but with a comparatively simpler gross structure. Ten progressions all with a frequency difference ∼2100 cm—1 have been found. Through a brief and qualitative discussion of the normal vibrations and symmetry properties of the molecule, the frequency differences ∼2100 cm—1 and ∼1900 cm—1 are respectively ascribed as the totally symmetrical v′c≡c(s) and unsymmetrical v′c≡c(a) longitudinal frequencies in the excited state. The frequency ∼635 cm—1 is assigned as one of the fundamental frequencies in the normal state, since bands with this frequency difference were relatively intensified at higher temperatures.

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