Microwave Detection of Interstellar Formaldehyde

Interstellar formaldehyde (${\mathrm{H}}_2$CO) has been detected in absorption against numerous galactic and extragalactic radio sources by means of the $1_{11}$-$1_{10}$ ground-state rotational transition at 4830 MHz. The absorbing regions often correspond in velocity with 18-cm OH features. ${\mathrm{H}}_2$CO is the first organic polyatomic molecule ever detected in the interstellar medium and its widespread distribution indicates that processes of interstellar chemical evolution may be much more complex than previously assumed.