orthoheliumn.
/ˌɔːθəʊˈhiːlɪəm/, /ˈɔːθəʊhiːlɪəm/, U.S. /ˈˌɔrθoʊˈˌhiliəm/ Physics.
The form of helium whose spectrum exhibits a fine structure of triplets owing to the spins of the two orbital electrons being parallel. Cf. parahelium n.
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the world > matter > physics > atomic physics > decomposition of light, spectrum > [noun] > multiplets in atomic spectra > helium with triplet fine structure
orthohelium1922
the world > matter > chemistry > elements and compounds > metals > noble gases > helium > [noun] > forms of
parahelium1896
orthohelium1922
1922 A. D. Udden tr. N. Bohr Theory of Spectra iii. iii. 86 Helium was at first assumed to be a mixture of two different gases, ‘orthohelium’ and ‘parhelium’, but now we know that the two spectra simply mean that the binding of the second electron can occur in two different ways.
1961 J. L. Powell & B. Crasemann Quantum Mech. xii. 458 Spectroscopically, the singlet and triplet systems are independent of one another, and have been given the names parahelium (singlets) and orthohelium (triplets). The ground state of the orthohelium system..is therefore stable with respect to optical transitions of the usual kind, and has a correspondingly long lifetime.
1974 G. Reece tr. F. Hund Hist. Quantum Theory iv. 60 Runge and Paschen were able to add series for O, S, Se and He in 1895–7. They discovered the two spectral systems of orthohelium and parahelium in the process.
1994 Physical Rev. A. 49 3234 It is quite interesting that the theoretical predictions of energy levels of parahelium in the S state are lower than the energy levels of orthohelium.
This entry has been updated (OED Third Edition, September 2004; most recently modified version published online March 2022).
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n.1922