The laboratory spectrum of acetaldehyde at 1 millimeter (230-325 GHz)

The rotational spectrum of acetaldehyde (CH3CHO) in the frequency range 230-325 GHz has been measured in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Over 250 transition frequencies are presented for this molecule for both A and E symmetry species in its ground (upsilon(sub t) = 0) and first excited (upsilon(sub t) = 1) torsional state, with experimental uncertainties of +/- 50 kHz. The data were fitted with a model involving an internal rotation potential function, which typically reproduces the measured frequencies to nu(sub obs) - nu(sub calc) less than or approximately 50 kHz for both ground and upsilon(sub t) = 1 state. These newly measured rest frequencies should aid in the identification of interstellar CH3CHO and in spectral line assignments for millimeter-band scans.