The symmetry of azodicarbonitrile

The infrared and Raman spectra of azodicarbonitrile (I) made from cyanogen azide (II) were recorded under varied conditions of phase, temperature, concentration, and pressure and strongly indicate a C_2h symmetry (trans-(I)). Cis-(I) was not shown positively either by these techniques or by microwave spectra. The fundamental vibration frequencies tentatively suggested for trans-(I) are (cm⁻¹): v₁ = 2176, v₂ = 1422, v₃ = 1002, v₄= 741, v₅ = 282 (A_g), v₆ = 108 (B_g, v₇ = 2204, v₈ = 982, v₉ = 904, v₁₀ = 596 (B_u), v₁₁ = 574, v₁₂ = 133 (A_u). Of these, v₄ and v₆ were not observed directly, but inferred from an analysis of a complex band in the infrared spectrum.