High-resolution infrared and submillimetre wave spectroscopic study of astrophysically significant methanol species (CD3OD): Intensity borrowed forbidden torsional fundamental band, hot band and overtone band transitions

Abstract

In this work, the systematic spectroscopic studies of methanol species have been continued in various frequency regions for the fully deuterated species (CD3OD). The main emphasis has been given to the high-resolution far-infrared (FIR) spectrum. The spectrum used has been recorded at room temperature (as opposed to −60 ℃ used previously) and slightly higher pressure to enhance the torsional hot and overtone band transitions. In total, about 1900 transitions have been assigned to definite quantum numbers and the assignments have been confirmed rigorously using the combination relations method. It was also possible to assign several sub-millimetre wave (SMMW) transitions in the 600 GHz region along with some forbidden torsional sub-bands. These forbidden transitions gain sufficient strength through the intensity borrowing effect from other transitions involving mixed resonant states. The assigned transitions include the torsional hot band, overtone band, and transitions in the second excited torsional states. The assigned transition wavenumbers have been used to obtain state-dependent molecular parameters. The reported transition wavenumbers in the FIR region have an estimated uncertainty of about ±0.0004cm-1 and the uncertainty of the SMMW frequencies is about ±50kHz. The complete atlas is presented in an Appendix submitted as the depository for the economy of space.