Table 3. Observed and calculated Raman vibrational frequencies (cm⁻¹) and mode assignments for crystalline di­acet­y­lene.

Assignment†	Mode	Exp. (90 K)	p-DFT (90 K)	Lit. (liquid ∼250 K)‡
ν4	CH asymmetric stretch	3281.4	3284.9	–
ν1	CH symmetric stretch	3273.1	3262.1	3293
ν2	CC triple-bond stretch	2173.9, 2178.9	2190.2, 2196.7	2172
ν3	CC single-bond stretch	873.5	883.4	877
ν8§	CCH bending	663.4	705.2	–
ν6	CCH bending	650.9	661.4	647
ν7	CCC bending	484.3	495.6	484
	Lattice vibration	96.0	124.5
	Lattice vibration	88.2 (sh)	118.2
	Lattice vibration	67.7	82.3, 98.2

^†Jones (1952 ▸) and Owen et al. (1987 ▸).

^‡Jones (1952 ▸).

^§Jolly et al. (2010 ▸).