An ab initio and spectroscopic study of dimethyl ether: An analysis of the infrared and Raman spectra

Abstract

We have calculated the potential surface with respect to the torsional angles of the methyl groups, the torsional energy level structure, and the infrared and overtone Raman intensities by ab initio methods using extended basis sets. The conclusions that were drawn from a correlation to the observed spectra are the following, (i) The modest basis set MP2/6-31G(d, p) yields a value of 238.32 cm−1 for the v16 gearing mode in reasonable agreement with the observed value of 241.0 cm−1. Extension of the basis set to MP2/6-311G(df, p) marginally improves this value to 239.36 cm−1. A somewhat larger basis set, RHF/6-311+G(3df, 3p) was needed for a satisfactory description of the components of the polarizability and the dipole moment. (ii) The technique of full relaxation of the coordinates of the top and the frame was unable to account for the strong resonance between the 2v12 overtone gearing level and the v7 COC in-plane bending mode. (iii) The asymmetry along the diagonals of the potential surface that determines the sign and magnitude of the sine.sine gearing term was found to display complex behaviour and was positive in the region of the eclipsed-eclipsed equilibrium conformation and negative for the staggered–staggered conformation.

Ab InitioDetermination of the Roto-Torsional Energy Levels oftrans-1,3-Butadiene

“…It has to be considered that the vibrational coordinate is defined as a single internal coordinate whereas it is not absolutely independent on the lowest neglected modes (as it occurs with the wagging of the number 9 and 10 hydrogens or with the torsion of the double bonds). Previous experiences show that the relaxed model fails when the interactions are relatively large (5)(6)(7)(8)(9). In these cases, there is a mix of coordinates in the optimization of the nonplanar structures and some internal coordinates appear to relax excessively.…”

Ab initio calculations and analysis of the torsional spectra of dimethylamine and dimethylphosphine

“…23 Fully and partially optimized ab initio calculations can be applied to verify the assignment of IR and Raman spectra. This technique was first employed for a set of molecules showing the G 36 symmetry and two C 3v symmetrical rotors such as thioacetone, 25 acetone, 26 biacetyl, 27 dimethyl-ether, 28,29 dimethyl-sulphide, 30 and butenes. 31 For that purpose, two and three dimension models were used.…”

CCSD(T) Study of CD3–O–CD3 and CH3–O–CD3 Far-Infrared Spectra

“…In the present paper, we analyze two DME isotopologues containing deuterium, 12 CD 3 -16 0-12 CD 3 (DME-d 6 ) and 12 CH 3 -16 0-12 CD 3 (DME-d 3 ), of which far-infrared and microwave spectra were recorded by Groner and Durig in the 1970s. 5 ' 14 Here, we review the former spectral assignments from a different point of view, the one provided by accurate ab initio calculations.…”