C4H -- name?
| It's a heavy molecule with no orbital momentum (L = 0) and thus follows momentum coupling scheme of Hund's case b: N + S = J, J + I = F. Here both electron spin S = 1/2 and nuclear spin I = 1/2 come from H atom. The levels with N = 1 and 2 are shown in Fig. 1 as an example. |  |
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