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

Abstract

The torsional Raman spectra of two astrophysically detected isotopologues of dimethyl ether (DME, 12 CH 3 O 12 CH 3 and 13 CH 3 O 12 CH 3 ) 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 2ν 11 and 2ν 15 with the COC-bending mode and the presence of many hot bands. The torsional overtones are set here at 2ν 11 =385.2 cm −1 and 2ν 15 =482.0 cm −1 for 12 CH 3 O 12 CH 3 and 2ν 11 =385.0 cm −1 and 2ν 15 =481.1 cm −1 for 13 CH 3 O 12 CH 3 . The new assignment of 2ν 11 is downshifted around ∼10cm −1 with respect to the literature. All the other (hot) bands have been reassigned consistently. In addition, the infrared-forbidden torsional fundamental band ν 11 is observed here at 197.8cm −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.

Ab initio spectroscopic characterization of the radical CH3OCH2 at low temperatures

“…More details concerning the theory implemented in ENEDIM theory, as well as examples of previous applications, can be found in Ref. [33][34][35][36][37][38].…”

The Far-Infrared Spectrum of Methoxymethanol (CH3–O–CH2OH): A Theoretical Study

“…They were computed to be 1206.6 cm –1 (Tt), 1405.1 cm –1 (Tc), and 2074.2 cm –1 (Ct), respectively . By comparing the behaviors of hydroxylamine and methoxymethanol, we obtain the same similarities and differences as when DME (ether) and acetone (ketone) , are compared. In methoxymethanol, the stability of the secondary minima and the interconversion through low barriers are noticeable.…”

“…The V 3 barriers of MeOCH 2 OH conformers (595.7:829:807.5 cm –1 ) can be compared with those of hydroxyacetone (72:472:340:57 cm –1 ) . The rate V 3 CH 3 OCH 2 OH / V 3 CH 3 COCH 2 OH is of the order of magnitude of V 3 DME / V 3 Acetone = 990:245 cm –1 . , Methyl torsional barriers are much higher in ethers than in ketones. For comparison, we provide barriers of other molecules containing similar functional groups such as isopropyl alcohol, peroxyacetic acid, methanol, and methyl acetate computed to be ∼1170, ∼89, ∼378, and ∼413 cm –1 , respectively.…”

“…The variational model has been employed for previous studies of other organic nonrigid species such as ethylene glycol, , isopropyl alcohol, peroxyacetic acid, and hydroxyacetone, CH 3 COCH 2 OH . This last ketone shares properties with the MeOCH 2 OH ether, in the same way as acetone and DME, which show two interacting methyl groups. , In this paper, we compare the behavior of these pairs of molecules. The energy levels allow us to compute the vibrational partition functions required by the radiative transfer models used for the interpretation of astrophysical observations …”

Ab Initio Study of the Large Amplitude Motions of Various Monosubstituted Isotopologues of Methylamine (CH3-NH2)

“…The aim of the present work is the theoretical study of probably detectable methylamine isotopologues. Monosubstituted isotopologues were detected for many astrophysical molecules such as dimethyl-ether and methyl-formate as it is described in the references provided by the papers of Fernández et al (2019) and Gámez et al (2019). In a recent study of the methylamine main isotopologue, highly correlated ab initio methods were employed to simulate the far infrared spectra (Senent 2018).…”