First reported high-resolution far-infrared spectral study of the CCO-bending mode of ethyl alcohol (CH3CH2OH), using synchrotron radiation

Abstract

In this work, the high-resolution (0.0002 cm⁻¹) far-infrared (FIR) Fourier transform spectrum corresponding to the CCO-bending band, centered around 420 cm-1, has been recorded using the Synchrotron radiation-assisted Fourier transform spectrometer at the Canadian Light Sources under various physical conditions. The spectrum used in this work was recorded at a lower temperature of −60 degrees C and demonstrates a high signal-to-noise (S/N) ratio. This made it possible to identify weak transition lines. The spectrum exhibits a typical parallel band structure, characterized by a well-defined Q-branch at approximately 420 cm-1, with P- and R-branches on either side. The complete spectrum in the range of 50–1200 cm-1 was covered in various runs under varied physical conditions, as discussed in detail in a later section. The spectra have been arranged in Loomis-Wood type arrangements to facilitate assignments of various sub-branches for (Kσ) states. In the spectrum, assignments have been carried out for K = 0 to 9, with J values up to 35 for the trans (e0) species. Asymmetry splitting has been observed for K = 1 through 4. Strong Q-branch lines have been observed. Corresponding Q-branch lines for higher K values have supported the assignments. About 500 transitions have been identified, and the term values for the bending mode have been determined accurately. The assignments have been confirmed using combination differences and comparing them with well-known ground state energy differences. The state-dependent molecular parameters for the bending state have been obtained. An extensive atlas of approximately 9000 spectral lines has been prepared as an appendix. Apart from being of fundamental value, this work will help identify Ethyl Alcohol in interstellar space (ISM) using infrared (IR) detectors on board JWST and Spitzer in the range of 0.6–38 μm. This paper represents the first high-resolution study of any vibrational mode of Ethanol other than the torsional modes.