NIST Physical Measurement Laboratory Handbook of Basic Atomic Spectroscopic Data

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Atomic Data for Helium (He)

Atomic Number = 2

Atomic Weight = 4.002602

Reference E95

Isotope  Mass     Abundance  Spin Mag Moment
3He 3.01603 0.000138% 1/2 -2.12762 4He 4.00260 99.999862% 0

The spectroscopic data below are for the isotope 4He.

He I  Ground State 1s2  1S0
      Ionization energy  198310.669 cm-1 (24.587387 eV)   Ref. M02
He II Ground State 1s  2S1/2
      Ionization energy  438908.8789 cm-1 (54.417760 eV)   Ref. MK00b