Enthalpy of formation (Hfg), Entropy, Integrated heat capacity (0 K to 298.15 K) (HH), Heat Capacity (Cp)

Property	Value	Uncertainty	units	Reference	Comment
Hfg(298.15K)	583.86	22.00	kJ mol-1	Gurvich
Hfg(0K)	580.00	22.00	kJ mol-1	Gurvich
Entropy (298.15K)	238.00		J K-1 mol-1	Gurvich
Integrated Heat Capacity (0 to 298.15K)	10.30		kJ mol-1	Gurvich
Heat Capacity (298.15K)	36.26		J K-1 mol-1	Gurvich

Information can also be found for this species in the NIST Chemistry Webbook

Vibrational levels (cm^-1)

Mode Number	Symmetry	Frequency (cm-1)	Frequency Reference	Intensity (km mol-1)	Int. unc.	Intensity Reference	Comment
1	Σg	511	VEEL5

Detailed diatomic data

ωe	ωexe	ωeye	Be	αe	ZPE	reference
510.98	2.02		0.239	0.00135	255.0223	2007Iri:389

vibrational zero-point energy: 255.5 cm^-1
Calculated vibrational frequencies for Si₂^- (silcon dimer anion).

Rotational Constants (cm^-1)
See section I.F.4 to change rotational constant units

A	B	C	reference	comment
	0.23900		1979HUB/HER

Calculated rotational constants for Si₂^- (silcon dimer anion).

Product of moments of inertia
70.53402	amu Å2		1.171263E-38	gm cm2

Geometric Data

Point Group D_∞h

Internal coordinates
distances (r) in Å, angles (a) in degrees, dihedrals (d) in degrees

Description	Value	unc.	Connectivity				Reference	Comment
			Atom 1	Atom 2	Atom 3	Atom 4
rSiSi	2.246		1	2			1979HUB/HER

Cartesians

Atom	x (Å)	y (Å)	z (Å)
Si1	0.0000	0.0000	0.0000
Si2	0.0000	0.0000	2.2460

Atom - Atom Distances
Distances in Å

	Si1	Si2
Si1		2.2460
Si2	2.2460

Calculated geometries for Si₂^- (silcon dimer anion).

Bond descriptions
Examples: C-C single bond, C=C, double bond, C#C triple bond, C:C aromatic bond

Bond Type	Count
Si#Si	1

Connectivity

Atom 1	Atom 2
Si1	Si2

Electronic energy levels (cm^-1)

Energy (cm-1)	Degeneracy	reference	description
0	3	1979HUB/HER	3Σg
669	6	1991Kit/Chi:1441	1Σg
3509	2	1991Kit/Chi:1441
4783	2	1991Kit/Chi:1441
5138	1	1991Kit/Chi:1441
9000	1	Gurvich
24428.98	3	Gurvich

Ionization Energies (eV)

Ionization Energy	I.E. unc.	vertical I.E.	v.I.E. unc.	Electron Affinity	E.A. unc.	reference
7.900				2.202	0.010	webbook

Dipole, Quadrupole and Polarizability
Electric dipole moment
For a molecule with D_∞h symmetry there is no dipole.
Electric quadrupole moment
Calculated electric quadrupole moments for Si₂^- (silcon dimer anion).

References
By selecting the following links, you may be leaving NIST webspace. We have provided these links to other web sites because they may have information that would be of interest to you. No inferences should be drawn on account of other sites being referenced, or not, from this page. There may be other web sites that are more appropriate for your purpose. NIST does not necessarily endorse the views expressed, or concur with the facts presented on these sites. Further, NIST does not endorse any commercial products that may be mentioned on these sites. Please address comments about this page to cccbdb@nist.gov.

squib	reference	DOI
1979HUB/HER	Huber, K.P.; Herzberg, G., Molecular Spectra and Molecular Structure. IV. Constants of Diatomic Molecules,, Van Nostrand Reinhold Co., 1979
1991Kit/Chi:1441	TN Kitsopoulos, CJ Chick, Y Zhao, DM Neumark "Study of low-lying electronic states of Si2 and Si2- using negative ion photodetachment techniques" J. Chem. Phys. 95(3), 1441, 1991	10.1063/1.461057
2007Iri:389	KK Irikura "Experimental Vibrational Zero-Point Energies: Diatomic Molecules" J. Phys. Chem. Ref. Data 36(2), 389, 2007	10.1063/1.2436891
Gurvich	Gurvich, L.V.; Veyts, I. V.; Alcock, C. B., Thermodynamic Properties of Individual Substances, Fouth Edition, Hemisphere Pub. Co., New York, 1989	10.1351/pac198961061027
VEEL5	M.E. Jacox, Vibrational and Electronic Energy Levels of Polyatomic Transient Molecules, J. Phys. Chem.Ref. Data, Monograph 3 (1994) (updated data in NIST Chemistry Webbook - http://webbook.nist.gov/chemistry/
webbook	NIST Chemistry Webbook (http://webbook.nist.gov/chemistry)

Got a better number? Please email us at cccbdb@nist.gov