Infra-Red and Raman Spectra of Diacetylene

• Published in: Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences Mathematical and physical sciences, 1952-02, Vol.211 (1105), p.285-295
• Main Author: Jones, A. Vallance
• Format: Article
• Language: English
• Subjects: Chemical bonding; Gas spectroscopy; Infrared spectrum; Lead; Liquids; Mathematical constants; Molecules; Raman scattering; Spectral bands; Vibrational spectra
• ISSN: 1364-5021; 0080-4630; 1471-2946; 2053-9169
• DOI: 10.1098/rspa.1952.0040

The infra-red spectrum of gaseous diacetylene has been investigated in the region 5000 to 500 cm-1 with a Perkin-Elmer spectrometer using prisms of lithium fluoride, sodium chloride and potassium bromide. The Raman spectrum of gaseous diacetylene has been investigated. The perpendicular Raman bands show the expected minima at the band centres, while the parallel bands have strong central Q branches. The Raman spectrum of liquid diacetylene has also been obtained and the depolarization ratios of the lines estimated. These investigations lead to a new assignment of the vibrational spectrum which accounts for the observed overtone and combination bands. In particular, a new Raman band found at 874 cm-1 has been assigned to the C—C stretching mode v3. A normal co-ordinate treatment has been carried out using the new assignment. This leads to a value for single bond C—C stretching force constant of 7∙1 × 105 dynes cm-1. Whereas previous calculations of this force constant based on earlier vibrational assignments had led to serious inconsistencies with the observed bond length and with the constants of cyanogen, the value obtained here appears satisfactory in all respects.