Rotational analysis of the nu(7) band in furan (C4H4O)

We recorded and analyzed the absorption spectrum of the v(7) fundamental ba nd in furan, observed around 995 cm(-1). Fourier transform Fl spectroscopy was used at ULB to record the spectrum under room-temperature conditions, a t 0.01 cm(-1) instrumental resolution. Diode-laser (DL) spectroscopy in a s upersonic jet was used to record some portions of the hand at Lille, reveal ing the fine structure around the band center. Pure rotation (MMW) data in the upper state were also recorded at Lille. Some 5559 FT, 101 DL, and 23 M MW data were assigned in this work. We fitted, on one hand, the MMW and DL data together and, on the other hand, the MMW DL, and FT data simultaneousl y using a weighted procedure, constraining the ground state constants to th eir value determined from the microwave data in the literature. The results from these fits are provided and the constants discussed. Ab initio calcul ations are also performed to provide a force field which is used to support the very strong increase with the vibrational excitation observed in the i nertial defect determined from the experimental rotational constants. (C) 1 999 Academic Press.