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Theoretical Characterization of Dimethyl Carbonate at Low Temperatures

AuthorsBoussessi, R. ; Guizani, S.; Senent, María Luisa ; Jaidane, N.
Issue Date31-Mar-2015
PublisherAmerican Chemical Society
CitationThe journal of physical chemistry, A, Molecules, spectroscopy, kinetics, environment & general theory 119: 4057- 4064 (2015)
Abstract© 2015 American Chemical Society. Highly correlated ab initio methods (CCSD(T) and RCCSD(T)-F12) are employed for the spectroscopic characterization of the gas phase of dimethyl carbonate (DMC) at low temperatures. DMC, a relevant molecule for atmospheric and astrochemical studies, shows only two conformers, cis−cis and trans−cis, respectively, of C2v and Cs symmetries. cis−cisDMC represents the most stable form. Using RCCSD(T)-F12 theory, the two sets of equilibrium rotational constants have been computed to be Ae = 10 493.15 MHz, Be = 2399.22 MHz, and Ce = 2001.78 MHz (cis−cis) and to be Ae = 6585.16 MHz, Be = 3009.04 MHz, and Ce = 2120.36 MHz (trans−cis). Centrifugal distortions constants and anharmonic frequencies for all of the vibrational modes are provided. Fermi displacements are predicted. The minimum energy pathway for the cis−cis → trans−cis interconversion process is restricted by a barrier of ∼3500 cm−1 . DMC displays internal rotation of two methyl groups. If the nonrigidity is considered, the molecule can be classified in the G36 (cis−cis) and the G18 (trans−cis) symmetry groups. For cis−cis-DMC, both internal tops are equivalent, and the torsional motions are restricted by V3 potential energy barriers of 384.7 cm−1 . trans−cis-DMC shows two different V3 barriers of 631.53 and 382.6 cm−1 . The far-infrared spectra linked to the torsional motion of both conformers are analyzed independently using a variational procedure and a two-dimensional flexible model. In cis−cis-DMC, the ground vibrational state splits into nine components: one nondegenerate, 0.000 cm−1 (A1), four quadruply degenerate, 0.012 cm−1 (G), and four doubly degenerate 0.024 cm−1 (E1 and E3). The methyl torsional fundamentals are obtained to lie at 140.274 cm−1 (ν15) and 132.564 cm−1 (ν30).
Description8 pags.; 3 figs.; 5 tabs.
Publisher version (URL)http://dx.doi.org/10.1021/acs.jpca.5b01836
Identifiersdoi: 10.1021/acs.jpca.5b01836
issn: 1520-5215
Appears in Collections:(CFMAC-IEM) Artículos
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