Microwave spectrum and structure of furfural

The microwave spectrum of furfural was investigated in the frequency range 7 GHz-21 GHz and 49 GHz-330 GHz. The ground and first torsional state of trans-furfural and ground state of cis-furfural were assigned and analyzed. A total of 1720 rotational lines with J up to 100 and Ka up to 53 were assigned to the ground state of trans-furfural, 1406 rotational lines with J up to 100 and Ka up to 48 were assigned to the first torsional state of trans-furfural and 2103 rotational lines with J up to 90 and Ka up to 48 to the ground state of cis-furfural. Accurate sets of centrifugal distortion constants for both conformations have been determined for the first time. The spectra of all 13C and 18O singly substituted isotopic species were observed in natural abundance in the 7 GHz-21 GHz range. Molecular structure co-ordinates, bond lengths and angles of the Kraitchman substitution type (rs) and pseudo-Kraitchman type (rpKr) are derived from the isotopic studies.