National Institute of Standards and Technology
Computational Chemistry Comparison and Benchmark DataBase
Release 17bSeptember 2015
NIST Standard Reference Database 101
IIExperimental data
IIICalculated data
IVData comparisons
VCost comparisons
VIInput and output files
VIITutorials and Units
VIIILinks to other sites
XOlder CCCBDB versions
XIII Vibrations
XIVReaction data
XVEntropy data
XVIBibliographic data
XVIIIon data
XVIIIBad calculations
XIXIndex of properties
XXH-bond dimers

NIST policy on privacy, security, and accessibility.

Please rate our products
© 2013 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

The National Institute of Standards and Technology (NIST) is an agency of the U.S. Department of Commerce.

Please send questions, comments, corrections, additions and suggestions to

return to home page

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

Listing of experimental data for HI (Hydrogen iodide)

Other names
Hydriodic acid; Hydroiodic acid; hydrogen iodide;
State Conformation
1Σ C*V
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 26.50 0.10 kJ mol-1 CODATA
Hfg(0K) enthalpy of formation 28.68 0.10 kJ mol-1 CODATA
Entropy (298.15K) entropy 206.59   J K-1 mol-1 webbook
Integrated Heat Capacity (0 to 298.15K) integrated heat capacity 8.66   kJ mol-1 Gurvich
Heat Capacity (298.15K) heat capacity 29.16   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 Σ 2309 webbook      

vibrational zero-point energy: 1154.5 cm-1
Calculated vibrational frequencies for HI (Hydrogen iodide).
Rotational Constants (cm-1) rotational constants
See section I.F.4 to change rotational constant units
A B C reference comment
  6.42637 6.42637 webbook

Calculated rotational constants for HI (Hydrogen iodide).

Product of moments of inertia moments of inertia
2.623199amu Å2   4.355992E-40gm cm2
Geometric Data
picture of Hydrogen iodide

Point Group C∞v

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
rHI 1.609 0.000 1 2 NISTdiatomic re


Atom x (Å) y (Å) z (Å)
I1 0.0000 0.0000 0.0000
H2 0.0000 0.0000 1.6092

Atom - Atom Distances bond lengths
Distances in Å

  I1 H2
I1   1.6092
H2 1.6092  

Calculated geometries for HI (Hydrogen iodide).

Bond descriptions

Examples: C-C single bond, C=C, double bond, C#C triple bond, C:C aromatic bond
Bond Type Count
H-I 1


Atom 1 Atom 2
I1 H2
Electronic energy levels (cm-1)
Energy (cm-1) Degeneracy reference description
0 1   1Σ

Ionization Energies (eV)

Ionization Energy I.E. unc. vertical I.E. v.I.E. unc. reference
10.386 0.001     webbook
Dipole, Quadrupole and Polarizability
Electric dipole moment dipole
Dipole (Debye) Reference comment
0.448 webbook  

Calculated electric dipole moments for HI (Hydrogen iodide).
Electric quadrupole moment quadrupole
Calculated electric quadrupole moments for HI (Hydrogen iodide).
Electric dipole polarizability (Å3) polarizability
alpha unc. Reference
5.453   1997Oln/Can:59

Calculated electric dipole polarizability for HI (Hydrogen iodide).

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
squib reference DOI
1997Oln/Can:59 TN Olney, NM Cann, G Cooper, CE Brion, Absolute scale determination for photoabsorption spectra and the calculation of molecular properties using dipole sum-rules, Chem. Phys. 223 (1997) 59-98 10.1016/S0301-0104(97)00145-6
CODATA Cox, J.D.; Wagman, D.D.; Medvedev, V.A.CODATA Key Values for Thermodynamics. Hemisphere, New York, 1989  
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
NISTdiatomic NIST Diatomic Spectral Database (  
webbook NIST Chemistry Webbook (  

Got a better number? Please email us at