Publication of Paper : The Journal of Physical Chemistry
Publié le : 2019-11-25 17:03:16


Publication of Paper : Journal of Physical Chemistry

DFT Study of Photochemical Properties and Radiative Forcing Efficiency Features of the Stereoisomers cis- and trans-CHCl-CH−CF3

Olivier Holtomo,*,†,‡
Ousmanou Motapon,‡
Mama Nsangou§

†Department of Physics, Faculty of Science, University of Bamenda, P.O. Box 39, Bambili, Cameroon
‡Department of Physics, Faculty of Science, University of Maroua, P.O. Box 814, Maroua, Cameroon
§Department of Physics, Higher Teachers Training College, University of Maroua, P.O. Box 46, Maroua, Cameroon

The accurate assessment of radiative forcing efficiency (RFE) of a greenhouse gas is based on the precise knowledge of its structure and infrared absorption spectrum. The present work investigates the UV−vis absorption
spectra and IR absorption spectra that are used for the determination of RFE of the short-lived compounds, cis- and trans-CHClCHCF3 (CTFP). These investigations were carried out with six different density functional theory
(DFT) methods B3LYP, CAM-B3LYP, M06, M06-2X, TPSS0, and ωB97X-D associated to the basis set 6-31G(3df). Therefrom, the relative populations of the two states cis and trans for temperatures over the range 220−370 K at 1
atm and along the atmospheric altitude were assessed. It turns out that trans-CTFP is the abundant component between the two states. This review reveals that B3LYP and M06 reproduce well the experimental results of UV−vis
spectra of trans-CTFP. As for cis-CTFP, EOM-CCSD is not well fitted by DFT methods. The cis- to trans-CTFP isomerization leads to the red shift for DFT methods and to the blue shift in regard to EOMCCSD and experimental results. The IR absorption spectra are well fitted by B3LYP over the range 500−1600 cm−1 and TPSS0
over 1300−2000 cm−1 for both stereoisomers. Moreover, the root-mean-square errors (RMSEs) of frequencies from
experimental data are lower for B3LYP and TPSS0 for both systems. The computed IR absorption band strengths over 500−2000 cm−1 for cis- and over 600−1800 cm−1 for trans-CTFP are consistent with the experiment. The relevant descriptor RFEs of the climate effect were calculated using a narrow band model for a constant vertical profile and then corrected with a lifetime factor for different computational methods. The computed values correlate well with the experimental results for both stereoisomers except M06-2X and TPSS0. It is worth noting that, for both systems, the intense radiative forcing spectra are located at frequencies ranging in 1000−1200 cm−1. The lower forcings of trans-CTFP lying in the atmospheric window region
800−1000 cm−1 are greater than those of cis-CTFP. Therefore, RFE(trans-CTFP) = 1.127 RFE(cis-CTFP).

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