Selected ATcT [1, 2] enthalpy of formation based on version 1.176 of the Thermochemical Network [3]

This version of ATcT results[3] was generated by additional expansion of version 1.172 to include species related to Criegee intermediates that are involved in several ongoing studies[4].

Disilicon

Formula: Si2 (g)

CAS RN: 12597-35-2

ATcT ID: 12597-35-2*0

SMILES: [Si][Si]

InChI: InChI=1S/Si2/c1-2

InChIKey: NTQGILPNLZZOJH-UHFFFAOYSA-N

Hills Formula: Si2

2D Image:

Aliases: Si2; Disilicon; Diatomic silicon; Silicon dimer

Relative Molecular Mass: 56.17100 ± 0.00060

Δ_fH°(0 K)	Δ_fH°(298.15 K)	Uncertainty	Units
587.5	591.3	± 1.6	kJ/mol

3D Image of Si2 (g)

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Top contributors to the provenance of Δ_fH° of Si2 (g)

The 20 contributors listed below account only for 86.3% of the provenance of Δ_fH° of Si2 (g).
A total of 25 contributors would be needed to account for 90% of the provenance.

Please note: The list is limited to 20 most important contributors or, if less, a number sufficient to account for 90% of the provenance. The Reference acts as a further link to the relevant references and notes for the measurement. The Measured Quantity is normaly given in the original units; in cases where we have reinterpreted the original measurement, the listed value may differ from that given by the authors. The quoted uncertainty is the a priori uncertainty used as input when constructing the initial Thermochemical Network, and corresponds either to the value proposed by the original authors or to our estimate; if an additional multiplier is given in parentheses immediately after the prior uncertainty, it corresponds to the factor by which the prior uncertainty needed to be multiplied during the ATcT analysis in order to make that particular measurement consistent with the prevailing knowledge contained in the Thermochemical Network.

Contribution (%)	TN ID	Reaction	Measured Quantity	Reference
34.7	8487.8	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 74.96 ± 0.30 kcal/mol	Feller 2008
8.7	8538.1	Si (cr,l) + 2 F2 (g) → SiF4 (g)	Δ_rH°(298.15 K) = -385.98 ± 0.19 kcal/mol	Wise 1963, Wise 1963, Wise 1962
6.9	8487.7	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 74.2 ± 0.4 (×1.682) kcal/mol	Feller 1999a, Feller 1999a
3.8	8481.2	Si (cr,l) → Si (g)	Δ_rG°(1525 K) = 231.1 ± 2.0 kJ/mol	Batdorf 1959, 3rd Law
3.5	8631.1	SiH3SiH3 (g) → 2 Si (cr,l) + 3 H2 (g)	Δ_rH°(298.15 K) = -19.1 ± 0.6 (×1.61) kcal/mol	Gunn 1961, est unc
3.4	546.1	SiF4 (g) + 2 H2O (cr,l) → Si (cr,l) + O2 (g) + 4 HF (aq, 5 H2O)	Δ_rH°(298.15 K) = 899.77 ± 1.20 kJ/mol	Paulechka 2020, Vorobev 1960, Hummel 1959, Johnson 1987, Good 1964, Good 1964, Johnson 1973
3.2	8595.1	SiH4 (g) → Si (cr,l) + 2 H2 (g)	Δ_rH°(298.15 K) = -8.3 ± 0.5 kcal/mol	Gunn 1961, Gurvich TPIS, est unc
2.4	8516.6	SiO2 (cr,l) + Si (cr,l) → 2 SiO (g)	Δ_rG°(1618 K) = 37.94 ± 0.29 kcal/mol	Ramstad 1961, 3rd Law, Gurvich TPIS
2.4	8538.3	Si (cr,l) + 2 F2 (g) → SiF4 (g)	Δ_rH°(298.15 K) = -1615.78 ± 0.46 (×3.292) kJ/mol	Johnson 1986, Johnson 1986
2.0	8508.5	SiO (g) → Si (g) + O (g)	Δ_rH°(0 K) = 189.99 ± 0.30 kcal/mol	Feller 2008
2.0	8508.10	SiO (g) → Si (g) + O (g)	Δ_rH°(0 K) = 190.23 ± 0.30 kcal/mol	Karton 2011
2.0	8492.1	Si (cr,l) + Si (g) → Si2 (g)	Δ_rG°(1800 K) = 13.9 ± 1.9 kcal/mol	Chatillon 1975, 3rd Law
1.9	8499.1	Si (cr,l) + O2 (g) → SiO2 (cr,l)	Δ_rH°(298.15 K) = -217.58 ± 0.35 (×1.164) kcal/mol	Good 1964, Good 1964, Good 1962, King 1951
1.5	8535.8	SiF4 (g) → Si (g) + 4 F (g)	Δ_rH°(0 K) = 565.92 ± 0.30 kcal/mol	Karton 2011
1.4	8481.3	Si (cr,l) → Si (g)	Δ_rH°(1932 K) = 393.1 ± 2.5 (×1.297) kJ/mol	Drowart 1960, 2nd Law, Gurvich TPIS
1.3	8487.6	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 74.17 ± 1.50 kcal/mol	Ruscic W1RO
1.2	8487.4	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 75.15 ± 1.60 kcal/mol	Ruscic G4
1.1	8508.9	SiO (g) → Si (g) + O (g)	Δ_rH°(0 K) = 190.42 ± 0.40 kcal/mol	Karton 2011
1.0	8487.3	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 76.07 ± 1.72 kcal/mol	Ruscic G3X
0.9	8580.7	SiF4 (g) → SiF (g, doublet) + 3 F (g)	Δ_rH°(0 K) = 425.42 ± 0.25 kcal/mol	Karton 2007b

Top 10 species with enthalpies of formation correlated to the Δ_fH° of Si2 (g)

Please note: The correlation coefficients are obtained by renormalizing the off-diagonal elements of the covariance matrix by the corresponding variances.
The correlation coefficient is a number from -1 to 1, with 1 representing perfectly correlated species, -1 representing perfectly anti-correlated species, and 0 representing perfectly uncorrelated species.

Correlation Coefficent (%)	Species Name	Formula	Δ_fH°(0 K)	Δ_fH°(298.15 K)	Uncertainty	Units	Relative Molecular Mass	ATcT ID
89.9	Disilicon anion	[Si2]- (g)	375.1	379.0	± 1.7	kJ/mol	56.17155 ± 0.00060	64236-73-3*0
71.3	Silicon	Si (g)	450.34	454.68	± 0.56	kJ/mol	28.08550 ± 0.00030	7440-21-3*0
71.3	Silicon anion	Si- (g)	316.28	319.26	± 0.56	kJ/mol	28.08605 ± 0.00030	14337-02-1*0
71.3	Silicon cation	Si+ (g)	1236.86	1240.99	± 0.56	kJ/mol	28.08495 ± 0.00030	14067-07-3*0
71.3	Silicon atom dication	[Si]+2 (g)	2814.00	2816.98	± 0.56	kJ/mol	28.08440 ± 0.00030	14175-55-4*0
71.3	Silicon atom tetracation	[Si]+4 (g)	10401.10	10404.08	± 0.56	kJ/mol	28.08331 ± 0.00030	22537-24-2*0
71.3	Silicon atom trication	[Si]+3 (g)	6045.58	6048.56	± 0.56	kJ/mol	28.08385 ± 0.00030	14175-56-5*0
64.0	Disilicon cation	[Si2]+ (g)	1352.3	1355.9	± 2.4	kJ/mol	56.17045 ± 0.00060	12597-36-3*0
61.2	Disilane	SiH3SiH3 (g)	92.0	75.9	± 1.3	kJ/mol	62.21864 ± 0.00073	1590-87-0*0
60.9	Silane	SiH4 (g)	42.66	33.04	± 0.63	kJ/mol	32.11726 ± 0.00041	7803-62-5*0

Most Influential reactions involving Si2 (g)

Please note: The list, which is based on a hat (projection) matrix analysis, is limited to no more than 20 largest influences.

Influence Coefficient	TN ID	Reaction	Measured Quantity	Reference
0.728	8487.8	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 74.96 ± 0.30 kcal/mol	Feller 2008
0.590	8489.1	[Si2]- (g) → Si2 (g)	Δ_rH°(0 K) = 2.202 ± 0.010 eV	Arnold 1993, Kitsopoulos 1991
0.409	8489.2	[Si2]- (g) → Si2 (g)	Δ_rH°(0 K) = 2.199 ± 0.012 eV	Nimlos 1987
0.373	8534.4	SiC (g) + [Si2]+ (g) → [SiC]+ (g) + Si2 (g)	Δ_rH°(0 K) = 1.033 ± 0.030 eV	Ruscic W1RO
0.225	8488.6	Si2 (g) → [Si2]+ (g)	Δ_rH°(0 K) = 7.905 ± 0.040 eV	Ruscic W1RO
0.144	8487.7	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 74.2 ± 0.4 (×1.682) kcal/mol	Feller 1999a, Feller 1999a
0.139	8534.2	SiC (g) + [Si2]+ (g) → [SiC]+ (g) + Si2 (g)	Δ_rH°(0 K) = 1.001 ± 0.049 eV	Ruscic G4
0.087	8534.1	SiC (g) + [Si2]+ (g) → [SiC]+ (g) + Si2 (g)	Δ_rH°(0 K) = 1.015 ± 0.062 eV	Ruscic G3X
0.067	8488.4	Si2 (g) → [Si2]+ (g)	Δ_rH°(0 K) = 7.924 ± 0.073 eV	Ruscic G4
0.041	8488.3	Si2 (g) → [Si2]+ (g)	Δ_rH°(0 K) = 7.895 ± 0.093 eV	Ruscic G3X
0.035	8534.3	SiC (g) + [Si2]+ (g) → [SiC]+ (g) + Si2 (g)	Δ_rH°(0 K) = 1.140 ± 0.066 (×1.477) eV	Ruscic CBS-n
0.033	8534.5	SiC (g) + [Si2]+ (g) → [SiC]+ (g) + Si2 (g)	Δ_rH°(0 K) = 1.03 ± 0.10 eV	Bruna 1981, est unc
0.030	8488.5	Si2 (g) → [Si2]+ (g)	Δ_rH°(0 K) = 7.819 ± 0.099 (×1.091) eV	Ruscic CBS-n
0.029	8487.6	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 74.17 ± 1.50 kcal/mol	Ruscic W1RO
0.025	8487.4	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 75.15 ± 1.60 kcal/mol	Ruscic G4
0.022	8492.1	Si (cr,l) + Si (g) → Si2 (g)	Δ_rG°(1800 K) = 13.9 ± 1.9 kcal/mol	Chatillon 1975, 3rd Law
0.022	8487.3	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 76.07 ± 1.72 kcal/mol	Ruscic G3X
0.018	8532.2	2 SiC (cr, alpha-hex) → Si2 (g) + 2 C (graphite)	Δ_rH°(2000 K) = 165 ± 5 (×1.044) kcal/mol	Drowart 1958, 3rd Law
0.016	8488.1	Si2 (g) → [Si2]+ (g)	Δ_rH°(0 K) = 8.00 ± 0.15 eV	Winstead 1995, Winstead 1995a, est unc
0.014	8487.5	Si2 (g) → 2 Si (g)	Δ_rH°(0 K) = 73.29 ± 2.16 kcal/mol	Ruscic CBS-n

References

1		B. Ruscic, R. E. Pinzon, M. L. Morton, G. von Laszewski, S. Bittner, S. G. Nijsure, K. A. Amin, M. Minkoff, and A. F. Wagner, Introduction to Active Thermochemical Tables: Several "Key" Enthalpies of Formation Revisited. J. Phys. Chem. A 108, 9979-9997 (2004) [DOI: 10.1021/jp047912y]
2		B. Ruscic, R. E. Pinzon, G. von Laszewski, D. Kodeboyina, A. Burcat, D. Leahy, D. Montoya, and A. F. Wagner, Active Thermochemical Tables: Thermochemistry for the 21^st Century. J. Phys. Conf. Ser. 16, 561-570 (2005) [DOI: 10.1088/1742-6596/16/1/078]
3		B. Ruscic and D. H. Bross, Active Thermochemical Tables (ATcT) values based on ver. 1.176 of the Thermochemical Network (2024); available at ATcT.anl.gov
4		T. L. Nguyen et al, ongoing studies (2024)
5		B. Ruscic, Uncertainty Quantification in Thermochemistry, Benchmarking Electronic Structure Computations, and Active Thermochemical Tables. Int. J. Quantum Chem. 114, 1097-1101 (2014) [DOI: 10.1002/qua.24605]
6		B. Ruscic and D. H. Bross, Thermochemistry Computer Aided Chem. Eng. 45, 3-114 (2019) [DOI: 10.1016/B978-0-444-64087-1.00001-2]

Formula

The aggregate state is given in parentheses following the formula, such as: g - gas-phase, cr - crystal, l - liquid, etc.

Uncertainties

The listed uncertainties correspond to estimated 95% confidence limits, as customary in thermochemistry (see, for example, Ruscic [5] and Ruscic and Bross[6]).
Note that an uncertainty of ± 0.000 kJ/mol indicates that the estimated uncertainty is < ± 0.000₅ kJ/mol.

Website Functionality Credits

The reorganization of the website was developed and implemented by David H. Bross (ANL).
The find function is based on the complete Species Dictionary entries for the appropriate version of the ATcT TN.
The molecule images are rendered by Indigo-depict.
The XYZ renderings are based on Jmol: an open-source Java viewer for chemical structures in 3D. http://www.jmol.org/.

Acknowledgement

This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Contract No. DE-AC02-06CH11357.