  We present a clear detection of CH2 in absorption towards the molecular cloud
complexes Sagittarius B2 and W49 N using the ISO Long Wavelength Spectrometer.
These observations represent the first detection of its low excitation
rotational lines in the interstellar medium. Towards Sagittarius B2, we detect
both ortho and para transitions allowing a determination of the total CH2
column density of N(CH2)=(7.5+/-1.1)x10^14 cm^-2. We compare this with the
related molecule, CH, to determine [CH/CH2]=2.7+/-0.5. Comparison with chemical
models shows that the CH abundance along the line of sight is consistent with
diffuse cloud conditions and that the high [CH/CH2] ratio can be explained by
including the effect of grain-surface reactions.
