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II.A.1. (XV.A.)

Listing of experimental data for Si2 (Silicon diatomic)

Other names
Silicon dimer; silicon dimer ; disilicon;
InChI=1/Si2/c1-2 [Si]=[Si] disilicon
State Conformation
3Σg D*H
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) enthalpy of formation 583.86 22.00 kJ mol-1 Gurvich
Hfg(0K) enthalpy of formation 580.00 22.00 kJ mol-1 Gurvich
Entropy (298.15K) entropy 238.00   J K-1 mol-1 Gurvich
Integrated Heat Capacity (0 to 298.15K) integrated heat capacity 10.30   kJ mol-1 Gurvich
Heat Capacity (298.15K) heat capacity 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) vibrations
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 (Silicon diatomic).
Rotational Constants (cm-1) rotational constants
See section I.F.4 to change rotational constant units
A B C reference comment
  0.23900   1979HUB/HER

Calculated rotational constants for Si2 (Silicon diatomic).

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

Geometric Data
picture of Silicon diatomic

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 re

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

Atom - Atom Distances bond lengths
Distances in Å
  Si1 Si2
Si1   2.2460
Si2 2.2460  

Calculated geometries for Si2 (Silicon diatomic).

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

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. reference
7.900       webbook

Electron Affinity (eV)
Electron Affinity unc. reference
2.202 0.010 webbook

Dipole, Quadrupole and Polarizability
Electric dipole moment dipole
For a molecule with D∞h symmetry there is no dipole.
Electric quadrupole moment quadrupole
Calculated electric quadrupole moments for Si2 (Silicon diatomic).

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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 -  
webbook NIST Chemistry Webbook (  

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