CCCBDB listing of experimental data page 2

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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	A_g	3140		webbook				CH str
2	A_g	1678		webbook				C=C str
3	A_g	1059		webbook				CH def
4	A_g	989		webbook				CH def
8	B_1u	3124		webbook				CH str
9	B_1u	1527		webbook				C=C str
10	B_1u	1028		webbook				CH def
11	B_2g	531		webbook				CH OPLA
12	B_2u	3105		webbook				CH str
13	B_2u	1244		webbook				CH def
14	B_2u	719		webbook				ring def
15	B_3g	3093		webbook				CH str
18	B_3u	576		webbook				CH OPLA

Bond Type	Count
H-C	4
C-C	2
C=C	2

Atom 1	Atom 2
C1	C2
C1	C3
C1	H5
C2	C4
C2	H6
C3	C4
C3	H7
C4	H8

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	¹A_g	D_2h	True							D_2h	0	2
1	2	¹A_1g	D_4h	False							D_4h	0	1

State	Config	State description	Conf description	Exp. min.	Quadrupole (D Å)			Reference	comment	Point Group	Components
State	Config	State description	Conf description	Exp. min.	xx	yy	zz	Reference	comment	Point Group	dipole	quadrupole
1	1	¹A_g	D_2h	True						D_2h	0	2
1	2	¹A_1g	D_4h	False						D_4h	0	1

	Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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Calc. vs exp. Bad Vib. HF vs MP2 Bad scale factors Low excited states Oddities NaCN Is not linear FAQ Help Units Choose Units Energy Bond length Rotational Constant Moment of Inertia Dipole and Quadrupole Polarizability Explanations Hartree cm-1 Debye Credits Just show me Show me a calculated geometry Summary Using older interface Limit Basis sets Method options List Recent molecules Choose a few Molecules Number of atoms By heavy atoms Diatomics InChI Deuterated Dimers Geometry Point group Point group count Bonds types Isodesmic reactions Bad point group Multiple conformers, states Vibrations Big anharmonicity Energy Enthalpy at 0 Kelvin Similar molecules Similar Isomers Cis/trans Tautomers Multiple conformers, states Ions, Dipoles, etc. List Ions Ionization changes point group Dipole Quadrupole Polarizability Proton Affinities Index of CCCBDB Feedback Error form Wants
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Experimental data for C4H4 (cyclobutadiene)

Experimental data for C₄H₄ (cyclobutadiene)