New Spectral Characterization of Dimethyl Ether Isotopologues CH3OCH3 and 13CH3OCH3 in the THz Region

9 pags., 2 figs., 3 tabs.The torsional Raman spectra of two astrophysically detected isotopologues of dimethyl ether (DME, 12CH3O12CH3 and 13CH3O12CH3) have been recorded at room temperature and cooled in a supersonic jet and interpreted with the help of highly correlated ab initio calculations. DME displays excited torsional and vibrational levels at low energy that can be populated at the temperatures of the star-forming regions, obliging to extend the analysis of the rotational spectrum over the ground state. Its spectrum in the THz region is rather complex due to the coupling of the torsional overtones 2ν11 and 2ν15 with the COC-bending mode and the presence of many hot bands. The torsional overtones are set here at 2ν11=385.2 cm−1 and 2ν15=482.0 cm−1 for 12CH3O12CH3 and 2ν11=385.0 cm−1 and 2ν15=481.1 cm−1 for 13CH3O12CH3. The new assignment of 2ν11 is downshifted around ∼10cm−1 with respect to the literature. All the other (hot) bands have been reassigned consistently. In addition, the infrared-forbidden torsional fundamental band ν11 is observed here at 197.8cm−1. The new spectral characterization in the THz region reported here provides improved values of the Hamiltonian parameters to be used in the analysis of the rotational spectra of DME isotopologues for further astrophysical detections.This research is supported by the Spanish Ministerio de Economía y Competitividad (MINECO) under Grants FIS2014-53448-C2-2-P, FIS2016-76418-P and FIS2017- 84391-C2, and is partially financed by the Spanish Junta de Andalucía and the European Regional Development Fund (ERDF) under Grant SOMM17/6105/UGR. The authors also acknowledge the European COST Actions CM1401 “Our Astrochemical History” and CM1405 “MOLIM” and CTI (CSIC) and CESGA for computing facilities.Peer reviewe