We have observed the J=5-4 ground state transition of FeO at a frequency of 153 GHz towards a selection of galactic sources .
Towards the galactic center source SgrB2 , we see weak absorption at approximately the velocity of other features towards this source ( 62 { km s } ^ { -1 } LSR ) .
Towards other sources , the results were negative as they were also for MgOH ( 3-2 ) and FeC ( 6-5 ) .
We tentatively conclude that the absorption seen toward SgrB2 is due to FeO in the hot ( \sim 500 K ) relatively low density absorbing gas known to be present in this line of sight .
This is the first ( albeit tentative ) detection of FeO or any iron–containing molecule in the interstellar gas .
Assuming the observed absorption to be due to FeO , we estimate [ FeO ] / [ SiO ] to be of order or less than 0.002 and [ FeO ] / [ { H } _ { 2 } ] of order 3 10 ^ { -11 } .
This is compatible with our negative results in other sources .
Our results suggest that the iron liberated from grains in the shocks associated with SgrB2 remains atomic and is not processed into molecular form .