Torsion–rotation global analysis and database for the CH 318OH isotopomer of methanol

Abstract

Fourier-transform far-infrared spectra of CH 3 18OH 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 ( ν t = 0, 1, and 2) of the CH 3 18OH 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 ν 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.