A search for the 55 MHz OH line
  The OH molecule, found abundantly in the Milky Way, has four transitions at
the ground state rotational level(J = 3/2) at cm wavelengths. These are E1
transitions between the F+ and F- hyperfine levels of the Lambda doublet of the
J=3/2 state. There are also forbidden M1 transitions between the hyperfine
levels within each of the doublet states occuring at frequencies 53.171 MHz and
55.128 MHz. These are extremely weak and hence difficult to detect. However
there is a possibility that the level populations giving rise to these lines
are inverted under special conditions, in which case it may be possible to
detect them through their maser emission. We describe the observational
diagnostics for determining when the hyperfine levels are inverted, and
identify a region near W44 where these conditions are satisfied. A
high-velocity-resolution search for these hyperfine OH lines using the low
frequency feeds on four antennas of the GMRT and the new GMRT Software
Backend(GSB) was performed on this target near W44. We place a 3-sigma upper
limit of ~17.3 Jy (at 1 km/s velocity resolution) for the 55 MHz line from this
region. This corresponds to an upper limit of 3 X 10^8 for the amplification of
the Galactic synchrotron emission providing the background.
