Table 7.

Experimental and computed harmonic ω and anharmonic ν fundamental wavenumbers for diacetylene (in cm⁻¹)

State	Symm.	B3LYP[a]		B2PLYP[b]		HYBRID[b]		Expt.
		ω	ν	ω	ν	ω	ν	ν
	Σg	3466	3343	3477	3352	3463	3338	3332
		2278	2238	2234	2189	2243	2197	2189
		915	901	908	890	894	872	872
	Σu	3467	3344	3478	3353	3465	3339	3334
		2111	2078	2064	2028	2064	2027	2022
	∏g	659	647	645	638	636	627	626
		529	522	507	512	485	491	483
	∏u	665	654	651	640	640	628	628
		237	237	231	232	221	222	220

The vibrational states are indicated as. DFT calculations were done in conjunction of the AVTZ basis set. Within the hybrid scheme, the harmonic wavenumbers, obtained at the AE-CCSD(T)/cc-pCVQZ level, were taken from Ref.61, and the anharmonic force-field calculated in this work at the B2PLYP/AVTZ level. The experimental values were taken from Refs.⁶¹ and⁶³.

^[a]VPT2 values, no Fermi resonances identified with Martin's test.

^[b]GVPT2 values, one weakly interaction between and states.