A comprehensive study of the ground vibrational state of the C-13 substituted methanol using high-resolution Synchrotron radiation spectra: Perturbation, forbidden, torsional fundamental overtone, excited overtones, and hot overtones transitions.

This work represents a comprehensive study of the ground vibrational state of C-13 substituted methanol using very high-resolution far-infrared (FIR) and infrared (IR) Synchrotron Radiation spectra recorded with a very high signal-to-noise (S/N) ratio in the entire region from 40to5000cm-1, at the Canadian Light sources. High resolution combined with a high S/N ratio allowed the recording to be done with an unprecedented resolution of about 0.0017cm-1. The peak of the unblended spectral lines could be obtained with an estimated accuracy of ±5kHz. The torsional vibrational states have been analyzed in the first five torsional states (n = 0,1…4). Assignments have been obtained for K- values up to about 15 and J- values of about 35 for the three symmetry species (A,E1,andE2). Assignments below 40cm-1 were obtained from the earlier spectra at a lower resolution. The assigned transition line wave numbers were directly fitted to the term values of the quantum states involved. A significant perturbation has been seen in the spectra later associated with the intensity borrowing effects, resulting in "forbidden transitions" with ΔK as high as ±7. Coriolis interactions have analyzed the perturbations observed in various states. The assignments have been confirmed using closed combination loops and the term values obtained for a given state derived from different sharing transitions. The most exciting phenomenon observed is the finding of torsional overtone transitions. These overtone transitions include the first, second, and third overtones (n=2←0,3←0,and4←0) and their hot torsional counterparts, e.g., transitions starting from excited torsional states (3←1,4←1,and4←2). These overtone transitions become possible due to the anharmonicity of the potential well due to internal rotation. The overtone transitions also include many "forbidden transitions." About 19,000 lines have been assigned and included in determining accurate term values. A detailed 6th-order Hamiltonian and the various aspects of torsion-rotation-vibration distortion effects are discussed, including the asymmetry effects. A global Hamiltonian analysis, including all the excited torsional state transitions, was seen to diverge. However, a reduced data set of about 9,000 lines with lines up to the second excited states revealed reasonable Hamiltonian parameters, which adds some confidence to the present analysis. The pure torsional energies have been obtained in more direct observations up to the 4th torsional excited states. Most of the data and some relevant parts of the spectrum have been moved to three Appendices: I, II, and III. They are being submitted as supplementary material to conserve journal space. This work represents the most complete study of the ground vibrational state of this crucial interstellar methanol species. This work should help the detection of this molecular species in the interstellar space.