Very high-resolution Synchrotron radiation far infrared spectrum of C-13 methanol arising from the ground torsional vibrational state and evidence of avoided crossing due to ΔK = 4 interaction

Abstract

In this work, very high-resolution far-infrared (FIR) and infrared (IR) Synchrotron Radiation spectra of C-13 substituted methanol species have been recorded with very high signal-to-noise (S/N) ratio in the entire region from 40 to 5000 cm−1. High resolution allowed the recording to be done with an unprecedented resolution of about 0.0014 cm−1 which is on the order of the doppler width of the lines. The peak of the spectral lines could be obtained with an estimated accuracy of ± 5 KHz. Analysis of the spectra has been performed for quantum numbers associated with the torsional ground state. Assignments have been obtained for K- values up to about 15 and J- values of about 35 for the three symmetry species. Asymmetry splitting has been observed for low K transitions and accurate asymmetry splitting constants have been obtained. Including the available microwave (MW) and millimeter-wave (MMW) measurements, a complete set of spectral line assignments have been obtained for the ground torsional state of the vibrational state. Following J.K. Watson’s method [1] all the spectral lines have been fitted to the exact term values of the energy levels. Localized perturbation has been observed for K = 9 A and state mixing resulted in forbidden transitions through intensity borrowing. A complete atlas has been presented for all possible quantum numbers for the ground state levels and the accurate term values have been obtained for all possible states. According to our knowledge, this atlas represents the most accurate line positions for this species reported so far. In addition, the results have been applied to confirm and obtain very accurate wavenumbers for several FIR laser lines pumped by CO2 lasers. The present atlas may be useful as a secondary wavenumber standard in the FIR region and should be useful for astrophysical detection.