The molecular gas in the central region of our Galaxy has been studied
often and extensively on several scales. However, on the scale of the
complete central region or even on the scale of a few degrees only very
few molecular transitions have been mapped; the large extent of the
Galactic center region makes such surveys very time-consuming. So far,
relatively complete maps exist in 
(e.g.
Bitran 1987/Bitran et al. 1997;
Jackson et al. 1996; Uchida et al. 1997),
(e.g. Heiligman 1987;
Bally et al. 1987,
1988),
(Jackson et al. 1996), and 
(Oka et al. 1996). There are also maps covering at least a few degrees in
the OH 1665- and 1667-MHz ground state lines (Cohen & Few
1976; Cohen & Dent 1983), in
(Whiteoak & Gardner
1979; Zylka et al. 1992), and in 
(Bally et al. 1987, 1988). It is, of course,
desirable to obtain more information on the distribution and abundance of
other important molecules as tracers of physical properties toward the
central region of the Milky Way. Since the 
or 
transition of even 13 is in many cases saturated, it is interesting to
compare the distribution of the transition of 
, which
many studies have assumed to be always optically thick, with that of
the (at least on large scales, and in most cases also on small scales)
optically thin 
() line.
In this work, we present a large scale survey of the Galactic center
region in the transition of at 109.782160 GHz
(Lovas 1992). The survey was carried out using the 1.2m
Southern Millimeter-Wave Telescope (SMWT) at the Cerro Tololo Interamerican
Observatory (CTIO) near La Serena, Chile. This telescope was built for
large scale surveys of the southern sky, especially of the Galactic
center region. The receiver of the telescope was optimized for carbon
monoxide observations at 3 mm wavelength and has a tuning range from
109 GHz to 120 GHz. In this frequency range, the telescope has a
beamsize of about 9
and hence is the appropriate instrument
for large scale surveys. The SMWT and its northern twin telescope, the
1.2m Northern Millimeter-Wave Telescope (NMWT), now at the
Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge (Mass.),
U.S.A., have been used to map the complete Galactic plane and several
other regions of interest in (Dame et
al. 1987).
The survey presented here constitutes the first major observing project
in the rare isotopomer C18O to be carried out by one of the 1.2m
Millimeter-Wave Telescopes (MWTs). It covers the range from
l=-1
05 to +36 in Galactic longitude and the range from
b=-09 to +075 in Galactic latitude. In total, 357
positions were observed. The final spectra at each position consist of
an average of 12 or more individual spectra, altogether more than
6500 spectra were taken. Preliminary presentations of the data are
given in Dahmen et al. (1993), Linhart
(1994), and Mauersberger (1994), a first glance
of the complete data is presented in Dahmen et al.
(1996). Because of the large bandwidth of the backend, the
50,5-40,4 transition of isocyanic acid (HNCO) at 109.905573 GHz
(Lovas 1992) could be observed simultaneously with the
line as long as the emission did not appear at too
negative velocities. In addition, observations were
performed to directly compare the data obtained with the
1.2m SMWT in the configuration used to other data and, thus,
check the comparability and calibration of the data presented here.
In Sect. 2 (click here), the instrumentation of the 1.2m SMWT is
outlined. In Sect. 3 (click here), the observations and data
reduction are described. In Sect. 4 (click here), the results of
the -survey are presented. These consist of the
full set of survey spectra, spatial maps of integrated intensities,
longitude-velocity plots, and latitude-velocity plots. The section also
includes a morphological description of the features mapped. In
Sect. 5 (click here), the 
) data
are presented and described in the same way as the data. In
Sect. 6 (click here), the data are shown and compared to
other measurements. Finally, in
Sect. 7 (click here), preliminary conclusions are drawn from the
morphological information presented so far. A detailed analysis and
discussion of the data will be given in a follow-up paper
(Paper II, Dahmen et al. 1997).