Torsion-rotation global analysis and database for the (CH3OH)-O-18 isotopomer of methanol

Fourier-transform far-infrared spectra of (CH3OH)-O-18 in the 15-470 cm(-1) region have been analyzed by means of the Ritz assignment program. The far-infrared data have been combined with the literature microwave and millimeter-wave measurements in a full global fitting of the first three torsional states (v(t) = 0, 1, and 2) of the (CH3OH)-O-18 ground vibrational state. The fitted dataset includes 550 microwave and millimeter-wave lines and more than 17 000 Fourier-transform transitions covering the quantum number ranges J <= 30, K <= 15, and v(t) <= 2. With incorporation of 79 adjustable parameters, the global fit achieved convergence with an overall weighted standard deviation of 1.072, essentially to within the assigned measurement uncertainties of +/- 50 kHz for almost all of the microwave and millimeter-wave lines and +/- 6 MHz (0.0002 cm(-1)) to +/- 15 MHz (0.0005 cm(-1)) for the Fourier-transform far-infrared measurements. Based on the global fit results, a database has been compiled containing transition frequencies, quantum numbers, lower state energies and transition strengths. This database will provide support for present and future astronomical studies, such as the on-going Orion surveys in preparation for the launch of the Herschel Space Observatory, in identifying isotopic methanol contributions to interstellar spectra. (c) 2007 Elsevier Inc. All rights reserved.