Dihydrogen, ground rotational state

The even values of J correspond to antisymmetric wavefiinctions and must be combined with symmetric spin wavefunctions. The only allowed rotational states of spin paired, or antiparallel, (t4 ) dihydrogen are thus those with, J = 0, 2, 4... This defines para-hydrogen. There are 27+1 possible spin states for each acceptable J value and it follows from Eq. (6.7) that there is only one spin state for the para-hydrogen ground state, J=0. 

Fig. 6.4 The energies of the rotational states of dihydrogen in the field of Eq. (6.20), relative to the J = 0, ground state. Given as a function of the parameter a/B. A nominal value ofb = 0.2 B is used to remove the degeneracy in M.

The ions being stored in the trap for very long periods, they are usually radiatively deexdted on their ground state (electronic and vibrational). This is a great advantage of the technique. In dihydrogen, due to the very slow ortho-para conversion, both rotational states J=1 and are present in this experiment. However it is unclear if they are in the normal 3 1 ortho-para ratb or if some conversion does occur on the apparatus walls. 

---