The microwave spectrum of dichloroacetic acid

The microwave spectrum of dichloroacetic acid consists of many weak absorption lines, of which only a small number has been identified. From the measured frequencies only two rotational constants could be obtained. Determination of the nuclear quadrupole coupling constants of the two chlorine atoms was not possible, since no line splittings were observed.Isotopic substitution of the two chlorine and the two hydrogen atoms shows that the assigned absorption lines belong to the conformation with the hydrogen atom gauche with respect to the hydroxylic group, while the carboxylic group has the common trans geometry. Substitution of the hydrogen atom of the dichloromethyl group by deuterium decreases the inertial moment I_c by 0.2 u Ų, indicating that structure determinations can be hampered by vibrational effects to an almost incredible extent.