Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The hyperfine structure of the hydrogen molecular ion   Theoretical investigations of the hyperfine structure of the hydrogen
molecular ion (one electron and two protons) are discussed. The nuclear
spin-rotation interaction has been found to be of the same sign as in the
hydrogen molecule and the hyperfine transition frequencies can be accurately
predicted. With measurements of the hyperfine structure of the deuterium
molecular ion (or of HD+) it should be possible to obtain a value of the
deuteron quadrupole moment that could be compared with the values obtained from
the deuterium molecule and from nuclear theory.

26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex