CCCBDB listing of experimental data page 2

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Property	Value	Uncertainty	units	Reference
Hfg(298.15K)	464.00		kJ mol^-1	webbook
Hfg(0K)			kJ mol^-1	webbook
Entropy (298.15K)			J K^-1 mol^-1
Integrated Heat Capacity (0 to 298.15K)			kJ mol^-1
Heat Capacity (298.15K)	73.70	1.00	J K^-1 mol^-1	webbook

Mode Number	Symmetry	Frequency			Intensity			Comment	Description
Mode Number	Symmetry	Fundamental(cm^-1)	Harmonic(cm^-1)	Reference	(km mol^-1)	unc.	Reference	Comment	Description
1	Σ_g⁺	3293		Shim
2	Σ_g⁺	2184		Shim
3	Σ_g⁺	874		Shim
4	Σ_u⁺	3329		Shim
5	Σ_u⁺	2020		Shim
6	Π_g	627		Shim
7	Π_g	482		Shim
8	Π_u	630		Shim
9	Π_u	231		Shim

Description	Value	unc.	Connectivity				Reference	Comment
Description	Value	unc.	Atom 1	Atom 2	Atom 3	Atom 4	Reference	Comment
rCH	1.058		3	5			1976Hellwege(II/7)
rCC	1.205		1	3			1976Hellwege(II/7)
rCC	1.378		1	2			1976Hellwege(II/7)

Atom	x (Å)	y (Å)	z (Å)
C1	0.0000	0.0000	0.6890
C2	0.0000	0.0000	-0.6890
C3	0.0000	0.0000	1.8940
C4	0.0000	0.0000	-1.8940
H5	0.0000	0.0000	2.9520
H6	0.0000	0.0000	-2.9520

	C1	C2	C3	C4	H5	H6
C1		1.3780	1.2050	2.5830	2.2630	3.6410
C2	1.3780		2.5830	1.2050	3.6410	2.2630
C3	1.2050	2.5830		3.7880	1.0580	4.8460
C4	2.5830	1.2050	3.7880		4.8460	1.0580
H5	2.2630	3.6410	1.0580	4.8460		5.9040
H6	3.6410	2.2630	4.8460	1.0580	5.9040

	Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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State	Config	State description	Conf description	Exp. min.	Dipole (Debye)				Reference	comment	Point Group	Components
State	Config	State description	Conf description	Exp. min.	x	y	z	total	Reference	comment	Point Group	dipole	quadrupole
1	1	¹Σ_g	D_∞h	True	0.000	0.000	0.000	0.000			D_∞h	0	1
1	2	¹A_G	C_2h	False							C_∞v	1	1

squib	reference	DOI
1976Hellwege(II/7)	Hellwege, KH and AM Hellwege (ed.). Landolt-Bornstein: Group II: Atomic and Molecular Physics Volume 7: Structure Data of Free Polyatomic Molecules. Springer-Verlag. Berlin. 1976.
1992McN/Bru:11	D McNaughton DN Bruget "The high-resolution infrared spectrum of diacetylene and dicyanoacetylene" J. Mol. Struct. 273 (1992) 11-25	10.1016/0022-2860(92)87072-4
1998Gus/Rui:163	M Gussoni, R Rui, G Zerbi "Electronic and relaxation contribution to linear molecular polarizability. An analysis of the experimental values" J. Mol. Struct. 447 (1998) 163-215	10.1016/S0022-2860(97)00292-5
Shim	Shimanouchi, T. , Tables of Molecular Vibrational Frequencies, Consolidated Volu	10.6028/NBS.NSRDS.39
webbook	NIST Chemistry Webbook (http://webbook.nist.gov/chemistry)	10.18434/T4D303

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

Bond Type	Count
C-C	1
C#C	2
H-C	2

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Experimental data for C4H2+ (diacetlyene cation)

Experimental data for C₄H₂⁺ (diacetlyene cation)