Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: H3+ Between the Stars   The presence of H3+ in the interstellar medium was forecast almost four
decades ago. Almost three decades ago it was asserted that its reactions with
neutral molecular and atomic species directly lead to the production of many of
the interstellar molecules that have been discovered by radio and infrared
astronomers. With the recent detection of H3+ in interstellar space,
astronomers finally have direct confirmation of H3+ as the foundation of
ion-molecule interstellar chemistry. Although many questions remain to be
answered, it is clear that H3+is a unique tool for understanding the properties
of interstellar clouds.

15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics