Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theory of nuclear spin conversion in ethylene   First theoretical analysis of the nuclear spin conversion in ethylene
molecules (13^CCH4) has been performed. The conversion rate was found equal
approx. 3x10^{-4} 1/s*Torr, which is in qualitative agreement with the recently
obtained experimental value. It was shown that the ortho-para mixing in 13^CCH4
is dominated by the spin-rotation coupling. Mixing of only two pairs of
ortho-para levels were found to contribute significantly to the spin
conversion.

1
The categories of this paper are: cs
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th