Global analysis of [formula omitted] in the torsional ground state: Gauche-to gauche transitions and severe perturbation of highly excited torsional vibrational states and [formula omitted] and [formula omitted] forbidden transitions

Abstract

In this work, a global analysis of all possible transitions in the first three internal rotational – vibrational- rotational states in the ground vibrational state (e0,o1,ande1) of doubly deuterated asymmetric species of methanol (CHD2OH) has been performed. A total of about 15,000 spectral lines have been included in the analyses. The data included about 1200 microwave and millimeter-wave transition lines from low lying energy levels, and about 13,000 precisely obtained far infra-red (FIR) spectral lines obtained using the high-resolution Fourier transform infrared (FTIR) spectrometer at the University of Giessen and later using the Synchrotron radiation-based spectrometer at the Canadian light Sources. The estimated precision of the FIR line positions obtained is on the order of ±0.0004cm-1 . Excellent signal/noise ratio allowed quite weak features to be easily detected. The studied transitions span the axial rotational quantum numbers (K) ranging from 0 to 15 for all three symmetry species. In most cases, the sub-bands series could be followed up to a rotational quantum number (J) of about 35. The analysis yielded the basic molecular parameters and state-dependent molecular coefficients. The work has been extended to higher energy torsionally excited transitions highly perturbed by interaction with nearby states. These resulted in the identification of b-type and c-type “forbidden transitions” with ΔK=0 and +2 origination from intensity borrowing effects. For the economy of space, only the essential data have been included in the text and the rest are included in Appendices (Ia and 1b) as depository and can be had from the author on request via email.