Spectroscopic detection of isolated carbonic acid

Carbonic acid ( cis-trans H 2 CO 3 ) in the gas phase has been successfully produced in a supersonic jet using a pulsed discharge nozzle, and pure rotational transitions of this molecule have been observed by Fourier-transform microwave spectroscopy. Although the observed cis-trans conformer is not the global minimum structure, it is an important conformer as a starting point of its dissociation to CO 2 and H 2 O . Three deuterated isotopologues of the cis-trans conformer ( cis-trans HDCO 3 , cis-trans DHCO 3 , and cis-trans D 2 CO 3 ) have also been observed, yielding the r 0 structure of cis-trans H 2 CO 3 . The present result is accurate enough to be used in radio astronomical observations.