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State	Conformation	minimum conformation	conformer description	state description
1	1	no	D*H	¹Σ_g
1	2	yes	C2H	¹A_G

	hartrees
Energy at 0K	-152.825784
Energy at 298.15K
HF Energy	-152.442194
Nuclear repulsion energy	75.766512

Mode Number	Symmetry	Frequency (cm^-1)	Scaled Frequency (cm^-1)	IR Intensities (km mol^-1)
1	Σ_g	3429	3304	0.00
2	Σ_g	2244	2163	0.00
3	Σ_g	872	840	0.00
4	Σ_u	3429	3304	103.80
5	Σ_u	2034	1960	0.02
6	Π_g	562	542	0.00
6	Π_g	562	542	0.00
7	Π_g	807i	777i	0.00
7	Π_g	807i	777i	0.00
8	Π_u	506	488	123.37
8	Π_u	506	488	123.37
9	Π_u	121	117	0.04
9	Π_u	121	117	0.04

Atom	x (Å)	y (Å)	z (Å)
C1	0.000	0.000	0.699
C2	0.000	0.000	-0.699
C3	0.000	0.000	1.930
C4	0.000	0.000	-1.930
H5	0.000	0.000	3.004
H6	0.000	0.000	-3.004

	C1	C2	C3	C4	H5	H6
C1		1.3989	1.2306	2.6294	2.3042	3.7031
C2	1.3989		2.6294	1.2306	3.7031	2.3042
C3	1.2306	2.6294		3.8600	1.0737	4.9336
C4	2.6294	1.2306	3.8600		4.9336	1.0737
H5	2.3042	3.7031	1.0737	4.9336		6.0073
H6	3.7031	2.3042	4.9336	1.0737	6.0073

All results from a given calculation for C₄H₂ (Diacetylene)

using model chemistry: QCISD/6-31G

States and conformations

Conformer 1 (D*H)

Conformer 2 (C2H)

	Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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	hartrees
Energy at 0K	-152.826336
Energy at 298.15K	-152.825217
HF Energy	-152.440980
Nuclear repulsion energy	75.791997

Mode Number	Symmetry	Frequency (cm^-1)	Scaled Frequency (cm^-1)	IR Intensities (km mol^-1)
1	A_g	3435	3310	0.00
2	A_g	2247	2165	0.00
3	A_g	878	846	0.00
4	A_g	750	722	0.00
5	A_g	581	559	0.00
6	A_u	587	565	113.18
7	A_u	184	177	2.43
8	B_g	602	580	0.00
9	B_u	3435	3310	101.05
10	B_u	2038	1964	0.02
11	B_u	660	636	105.80
12	B_u	208	200	6.54

Atom	x (Å)	y (Å)
C1	-0.031	0.698
C2	0.031	-0.698
C3	0.031	1.928
C4	-0.031	-1.928
H5	0.010	3.001
H6	-0.010	-3.001

	C1	C2	C3	C4	H5	H6
C1		1.3983	1.2309	2.6263	2.3028	3.6994
C2	1.3983		2.6263	1.2309	3.6994	2.3028
C3	1.2309	2.6263		3.8563	1.0732	4.9289
C4	2.6263	1.2309	3.8563		4.9289	1.0732
H5	2.3028	3.6994	1.0732	4.9289		6.0017
H6	3.6994	2.3028	4.9289	1.0732	6.0017

atom1	atom2	atom3	angle		atom1	atom2	atom3	angle
C1	C2	C4	180.000		C1	C3	H5	180.000
C2	C1	C3	180.000		C2	C4	H6	180.000

atom1	atom2	atom3	angle		atom1	atom2	atom3	angle
C1	C2	C4	174.649		C1	C3	H5	176.054
C2	C1	C3	174.649		C2	C4	H6	176.054

All results from a given calculation for C4H2 (Diacetylene)

using model chemistry: QCISD/6-31G

States and conformations

Conformer 1 (D*H)

Conformer 2 (C2H)

All results from a given calculation for C₄H₂ (Diacetylene)