Synchrotron radiation far infrared spectrum of the astrophysically significant Ethanol (CH3CH2OH) molecule in the gauche states in the vibrational ground state and other infrared observations

Abstract

In this communication, the analyses of synchrotron radiation far infrared (FIR) spectrum corresponding to the gauche- ($e_{1}and{o}_1$) states of Ethyl Alcohol are reported. Detailed assignments have been performed for b-type transitions for K values ranging from 5 to 32 and up to a maximum J value of 50. The assignments confirmed the earlier microwave (MW) and millimeter wave (MMW) spectroscopic results. The transition wavenumbers have been used to determine the term values for the gauche-states involved for all the K and J values for which observation has been made. About 2000 spectral lines have been assigned, including some accurately calculated lines that fall in the MW and MMW regions. Although transitions between the trans-species and gauche species are not allowed in Ethanol, many resonances and level crossings of energy levels cause forbidden transitions. One such system of level crossings between $K=10o_1$ and $12e{e}_{0}0$ has been analyzed in detail, and the interaction coefficient determined. The state mixing seems quite strong and causes forbidden transitions $(\Delta K=0,2,3)$, including transitions for $\mathrm{trans}\leftrightarrow gauche$, have been found. In addition, many new strong transitions have been assigned, which belong to the trans-species. To extend our work to higher wave numbers to facilitate observations made by the infrared detector on board the James Webb Space Telescope (JWST), the analysis of the torsional fundamental band transitions (around $220{\mathrm{cm}}^{-1}$) for $o_2\leftarrow e_0$ and $o_2\leftarrow e_1$ has been taken up. Some of the assignments are discussed here. Lastly, the lower-lying vibrational bands centered around $425{\mathrm{cm}}^{-1}$ (CCO– bending mode) and the band at around $800{\mathrm{cm}}^{-1}$ (${\mathrm{CH}}_3-$ rocking mode) have been recorded. The CCO bending band shows an unmistakable parallel character for the trans-species. The assignment work on the CCO-bending band is in progress, and the assignments for $K=0andK=1(+and-)$ are included in this report. Accurate term values for the CCO-bending mode could be obtained. The results allowed the determination of the leading rotational constants for the trans-species in the excited vibrational state of the CCO-bending state. The complete known assigned lines of about 16,000 lines for the parent isotopomer and about 650 lines for 13 ${-C}_1$ and 13−$C_2$ (see graphical abstract) substituted Ethanol isotopomers are gathered in Appendix I and II, respectively. These atlases should be a valuable tool for further energy level analysis and astronomical detection of Ethanol in interstellar space.