The New Absorption System of Cyanogen Gas in the Near Ultraviolet. System I

Abstract

A new system of absorption bands has been found in the region λλ3020–2400 with an absorbing path of three meters and a pressure of two atmospheres. The gross structure of the system is comparatively simple. Two main progressions of bands with frequency differences 2050 cm^—1 and 895 cm^—1 have been found. The bands in these progressions can be accurately represented by a general formula: $${\mathrm{\nu =A+\omega }}_1^{\prime }{v}_1^{\prime }{\mathrm{+x}}_{11}^{\prime }{v}_1^{\text{′2}}{\mathrm{+\omega }}_2^{\prime }{v}_2^{\prime }{\mathrm{+x}}_{22}^{\prime }{v}_2^{\text{′2}}{\mathrm{+x}}_{12}^{\prime }{v}_1^{\prime }{v}_2^{\prime }$$ with A = 33,293.63, ω₁′+x₁′ = 895.75, ω₂′ = 2065.38, x₂₂′ = — 15.13 and x₁₂′ = — 8.00. The electronic excitation is mainly at the C – N bond. The structure of the molecule in the excited state, its normal frequencies and symmetry properties are also discussed. The frequency difference 2050 cm^—1 is considered as due to the totally symmetric longitudinal (C – N) vibration in the excited, state and a tentative assignment is suggested as follows: ν₁′ = 895 cm^—1, ν₂′ = 2050 cm^—1, ν₃′ = 1770 cm^—1, δ₂′(u) = 210 cm^—1. Other possible assignment has also been briefly discussed.