Module constants 

Physical constants, SI units.

Source for every value: CODATA 2022 recommended values, P. J. Mohr, D. B. Newell, B. N. Taylor, E. Tiesinga, “CODATA recommended values of the fundamental physical constants: 2022”, Rev. Mod. Phys. 97, 025002 (2025), doi:10.1103/RevModPhys.97.025002. Values marked “exact” are fixed by the 2019 SI redefinition; the rest carry their standard uncertainty in the doc comment.

Verified digit by digit on 2026-10-06 (#15) against NIST’s listing of the 2022 CODATA adjustment, https://physics.nist.gov/cuu/Constants/Table/allascii.txt (rows “elementary charge”, “Planck constant”, “speed of light in vacuum”, “Boltzmann constant”, “Avogadro constant”, “vacuum electric permittivity”, “fine-structure constant”, “electron mass”, “proton mass”, “atomic mass constant”, “Bohr radius”, “Hartree energy”, “electron mass energy equivalent”). Every stored value equals the listed one. HBAR and COULOMB_E2 are not stored values but expressions of the stored ones; the tests check them, and four stored values, against other rows of the same listing.

Constants

ATOMIC_MASS_UNIT

Atomic mass constant m_u (unified atomic mass unit), kg. CODATA 2022: 1.660 539 068 92(52)e-27.

AVOGADRO

Avogadro constant N_A, 1/mol. CODATA 2022: 6.022 140 76e23 (exact).

BOHR_RADIUS

Bohr radius a₀, m. CODATA 2022: 5.291 772 105 44(82)e-11.

BOLTZMANN

Boltzmann constant k_B, J/K. CODATA 2022: 1.380 649e-23 (exact).

COULOMB_E2

Coulomb constant e² / (4π ε₀), J m. Derived from ELEMENTARY_CHARGE (C) and VACUUM_PERMITTIVITY (F/m = C²/(J m)), so the unit is J m (about 2.307e-28 J m, i.e. 14.3996 eV Å). CODATA lists no row for this combination; its relative uncertainty is that of ε₀, 1.6e-10. This is the combination the screened-Coulomb interatomic potentials in the ion engine are written with.

ELECTRON_MASS

Electron mass m_e, kg. CODATA 2022: 9.109 383 7139(28)e-31.

ELECTRON_REST_ENERGY

Electron rest energy m_e c², J. CODATA 2022: 8.187 105 7880(26)e-14 (equivalently 0.510 998 950 69(16) MeV).

ELEMENTARY_CHARGE

Elementary charge e, C. CODATA 2022: 1.602 176 634e-19 (exact).

FINE_STRUCTURE

Fine-structure constant α, dimensionless. CODATA 2022: 7.297 352 5643(11)e-3.

HARTREE_ENERGY

Hartree energy E_h, J. CODATA 2022: 4.359 744 722 2060(48)e-18.

HBAR

Reduced Planck constant h / 2π, J s. Derived from the exact PLANCK; CODATA 2022 lists 1.054 571 817…e-34 (exact).

PLANCK

Planck constant h, J s. CODATA 2022: 6.626 070 15e-34 (exact).

PROTON_MASS

Proton mass m_p, kg. CODATA 2022: 1.672 621 925 95(52)e-27.

SPEED_OF_LIGHT

Speed of light in vacuum c, m/s. CODATA 2022: 299 792 458 (exact).

VACUUM_PERMITTIVITY

Vacuum electric permittivity ε₀, F/m. CODATA 2022: 8.854 187 8188(14)e-12.