Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of enhanced rate coefficients in the H$_2^+$ + H$_2$
  $\rightarrow$ H$_3^+$ + H reaction at low collision energies   The energy dependence of the rate coefficient of the H$_2^+\ + {\rm H}_2
\rightarrow {\rm H}_3^+ + {\rm H}$ reaction has been measured in the range of
collision energies between $k_\mathrm{B}\cdot 10$ K and $k_\mathrm{B}\cdot 300$
mK. A clear deviation of the rate coefficient from the value expected on the
basis of the classical Langevin-capture behavior has been observed at collision
energies below $k_\mathrm{B}\cdot 1$ K, which is attributed to the joint
effects of the ion-quadrupole and Coriolis interactions in collisions involving
ortho-H$_2$ molecules in the $j = 1$ rotational level, which make up 75% of the
population of the neutral H$_2$ molecules in the experiments. The experimental
results are compared to very recent predictions by Dashevskaya, Litvin, Nikitin
and Troe (J. Chem. Phys., in press), with which they are in agreement.

18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom