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From: Nemesio Rodriguez  nemesio@oan.es 
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\begin{document}
\thesaurus{08(10.03.1; 13.09.3; 13.09.4; 09.13.2; 09.03.1; 09.04.1)}
%\title{}
\title{Non-equilibrium H$_2$ ortho-to-para ratio in two
molecular clouds of the Galactic Center}
%\subtitle{ }
\author{N.J.~Rodr\'{\i}guez-Fern\'andez\inst{1},
J.~Mart\'{\i}n-Pintado\inst{1},
P.~de Vicente\inst{1}, A.~Fuente\inst{1},
S.~H\"uttemeister\inst{2},  T.L.~Wilson\inst{3,4}, \and
D.~Kunze\inst{5}}

\institute{Observatorio Astron\'omico Nacional (IGN), Apartado 1143,
E-28800, Alcal\'a de Henares, Spain (nemesio, martin, vicente,
fuente$@$oan.es)
\and Astronomische Institute, Auf dem Huegel 71, D-53121 Bonn 1, Germany

(huette@astro.uni-bonn.de)
\and Max--Planck Institut f\"ur Radioastronomie, Postfach 2024, D 53010
Bonn,
\and Sub-mm Telescope Observatory, Steward Observatory, The University
of Arizona, Tucson, Az, 85728, USA \\ (twilson@as.arizona.edu)
\and MPE, Giesenbachstrasse 1, D-85748 Garching, Germany
(kunze@mpe.mpg.de)}

\date{Received date; accepted date}

\maketitle

\markboth{ N.J. Rodr\'{\i}guez-Fern\'andez et al.: Non-LTE OTPR in two
GC clouds}{ }
\begin{abstract}
We present ISO observations of the S(0), S(1), S(2), and S(3) rotational
lines
of molecular hydrogen from  two molecular clouds near
the Galactic Center (GC). We have also measured continuum dust
emission at infrared wavelengths with ISO and
the rotational radio lines J=1--0 of $^{13}$CO and C$^{18}$O
 and J=2--1 of  C$^{18}$O
with the IRAM-30m telescope.  Using the dust continuum spectra
and the CO lines we derive a total visual extinction of $\sim$ 15-20
magnitudes
toward these GC clouds.
After correcting the H$_2$ data for extinction, the gas
temperatures are $\sim$ 250~K
and the column densities of warm gas are $\sim 2\times
10^{21}$~cm$^{-2}$.
This is the first direct measure of the H$_2$ column
 densities of the warm component;
with this, we  estimate an NH$_3$ abundance in the warm gas
 of $\sim 2~10^{-7}$.
The column density of warm gas is, at least, a factor of 100 larger than

the corresponding column densities derived from the  warm dust.
The observed ortho-to-para ratio (OTPR) is  $\sim$ 1, clearly below the
local thermodynamical equilibrium (LTE) OTPR for gas at 250 K of $\sim
3$.
Low velocity shocks ($\sim$ 10 km s$^{-1}$)
are the most likely explanation for the column densities of
warm gas and dust and the non-LTE H$_2$ OTPR.

\keywords{ISM: clouds -- ISM: molecules -- ISM: dust, extinction --
  Galaxy: center -- Infrared: ISM: continuum -- Infrared: ISM:
     lines and bands}
\end{abstract}






\end{document}




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