Rotational Analysis of the ν6 Band in Furan (C4H4O)

Abstract

Abstract We recorded and analyzed the absorption spectrum of the ν 7 fundamental band in furan, observed around 995 cm −1 . Fourier transform (FT) spectroscopy was used at ULB to record the spectrum under room-temperature conditions, at 0.01 cm −1 instrumental resolution. Diode–laser (DL) spectroscopy in a supersonic jet was used to record some portions of the band at Lille, revealing 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 MMW 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 simultaneously using a weighted procedure, constraining the ground state constants to their value determined from the microwave data in the literature. The results from these fits are provided and the constants discussed. Ab initio calculations are also performed to provide a force field which is used to support the very strong increase with the vibrational excitation observed in the inertial defect determined from the experimental rotational constants.