  Stephan's Quintet (SQ) is a system consisting of at least four interacting
galaxies which is well known for its complex dynamical and star formation
history. It possesses a rich intergalactic medium (IGM), where hydrogen clouds,
both atomic and molecular, associated with two starbursts (refered to as SQ A
and B) have been found. In order to study the extent, origin and fate of the
intergalactic molecular gas and its relation to the formation of stars outside
galaxies and Tidal Dwarf Galaxies (TDGs), we mapped with the IRAM 30m antenna
the carbon monoxide (CO) towards several regions of the IGM in SQ. In both SQ A
and B, we detected unusually large amounts of molecular gas (3.1 times 10^9
msun and 7 times 10^8 msun, respectively). In contrast, no significant CO
detection was achieved towards HII regions south of the pair NGC 7318a/b
despite their high H alpha luminosities. The molecular gas is very extended in
both SQ A and SQ B, over areas of between 15 and 25 kpc. The CO clouds seem to
have otherwise different properties and may be of a different nature. The
integrated CO line of SQ A is in particular much wider than in SQ B. Its CO
spectrum shows emission at two velocities (6000 and 6700 km s^{-1}) that are
coincident with two HI lines. The strongest emission at 6000 km s^{-1} is
however spatially offset from the HI emission and situated on a ridge
south-east of the starburst region. In SQ B the CO emission coincides with that
of tracers of star formation (halpha, 15 mu m and radio continuum). The CO peak
lies slightly offset from the HI peak towards a steep HI gradient. This is
indicating that the molecular gas is forming in-situ, possibly in a region of
compressed HI, with subsequent star formation. The star forming region at SQ B
is the object in SQ that most resembles a TDG.
