Interactions between carboxylic acids and aldehydes: a rotational study of HCOOH-CH2O.

The rotational spectrum of the 1:1 complex between formic acid and formaldehyde shows that the two units are linked together through a "classical" (OH···O) and a weak (CH···O) hydrogen bond. The molecular system appears quite rigid, and no effects of the internal motions have been observed in the spectrum.