Raman and infrared spectra of dimethyl ether 13C-isotopologue (CH3O13CH3) from a CCSD(T) potential energy surface

Abstract

So far, no experimental data of the infrared and Raman spectra of 13 C isotopologue of dimethyl ether are available. With the aim of providing some clues of its low-lying vibrational bands and with the hope of contributing in a next spectral analysis, a number of vibrational transition frequencies below 300 cm 1 of the infrared spectrum and around 400 cm 1 of the Raman spectrum have been predicted and their assignments were proposed. Calculations were carried out through an ab initio three dimensional potential energy surface based on a previously reported one for the most abundant dimethyl ether isotopologue (M. Villa et al., J. Phys. Chem. A 115 (2011) 13573). The potential function was vibrationally corrected and computed with a highly correlated CCSD(T) method involving the COC bending angle and the two large amplitude CH 3 internal rotation degrees of freedom. Also, the Hamiltonian parameters could represent a support for the spectral characterization of this species. Although the computed vibrational term values are expected to be very accurate, an empirical adjustment of the Hamiltonian has been performed with the purpose of anticipating some workable corrections to any possible divergence of the vibrational frequencies. Also, the symmetry breaking derived from the isotopic substitution of 13 C in the dimethyl ether was taken into account when the symmetrization procedure was applied.

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

“…The ab initio Hamiltonian was then refined in this work following three steps: (i) the adjustment of the bending fundamental close to the experimental value, (ii) the reassignment of the two torsional fundamentals and their overtones according to the new Raman spectra, and (iii) the assignment of the other observed bands and the subsequent global fit of the Hamiltonian. The main difference between the old Hamiltonians from Villa et al (2011) and Carvajal et al (2012) and the present one involves the second step. These three steps are detailed next.…”

“…Hence, the a a B , kinetic parameter was also corrected in all of the conformations. For DME and 13 C-DME, F was optimized to be 1.954 (Villa et al 2011;Carvajal et al 2012) to reproduce the experimental bending energy term values. This represents a coordinate correction lower than 2%.…”

“…The spectrum of cooled DME allowed us to assign unequivocally the torsional overtones and their first hot bands, amending some of the previous assignments. In turn, the new frequencies have been used to refine 3D quantum calculations, employing a state-of-the-art coupled-cluster theory with single and double substitutions (CCSD(T)) ab initio calculations (Villa et al 2011) and a torsion-torsion-bending Hamiltonian (Senent et al 1995b;Carvajal et al 2012). The new characterization provides improved values of the Hamiltonian parameters for the analysis of DME and 13 C-DME rotational spectra and future astrophysical detections.…”

“…Calculated with the refined Hamiltonian of this work. Calculated with the adjusted Hamiltonian ofCarvajal et al (2012).…”

Transformation Properties under the Operations of the Molecular Symmetry Groups G36 and G36(EM) of Ethane H3CCH3

“…1, with the aim of facilitating the solution of the rotation-vibration Schrödinger equation for ethane and related molecules. The MS group G 36 has been the subject of a number of studies (see, for example, [4,5]). The EMS group G 36 (EM) was studied in detail by Di Lauro and Lattanzi [6,7].…”