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Ab initio quantum–chemical computations of the absorption cross sections in HgX2 and HgXY (X,Y=Cl, Br, and I): Molecules of interest on the Earth’s atmosphere

Abstract

The electronic–structure properties of the low–lying electronic states and the absorption cross sections of mercury halides HgCl2, HgBr2, HgI2, HgBrCl, HgClI, and HgBrI have been determined within the UV–Vis spectrum range (170 nm ≤ λphoton ≤ 600 nm) by means of the complete–active–space self–consistent field/multi–state complete–active–space second–order perturbation theory/ spin–orbit restricted–active–space state–interaction (CASSCF/MS–CASPT2/SO–RASSI) quantum–chemical methodology, with the third–order Douglas–Kroll and Hess (DKH3) Hamiltonian and the atomic–natural–orbital relativistic–correlation–consistent (ANO–RCC) basis set, and a semiclassical computational strategy based on nuclear sampling for simulating the band shapes. Computed band energies show a good agreement with the available experimental data for HgX2 with errors around 0.1–0.2 eV; theoretical and experimental cross sections (σ) are within the same order of magnitude. For the mixed HgXY compounds, the present computed data allow to interpret previously proposed absorption bands estimated from the spectra of the parent molecules HgX2 and HgY2, measured in methanol solution. The analyses performed on the excited–state electronic structure and its changes around the Franck–Condon region allow to clearly rationalize the singlet–triplet mixing of the absorption bands and the heavy–atom effect of the Hg compunds. Furthermore, the present benchmark of HgX2 and HgXY absorption σ values together with the previous benchmark of the electronic–structure properties of HgBr2 [see S. P. Sitkiewicz, et al., J. Chem. Phys., 2016, 145, 244304] allow us to set up a methodological and computational protocol which shall be used for predicting the atmospheric absorption and photolysis properties of several Hg compounds present in the atmospheric cycle of Hg.

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Publication details

The article was received on 02 Oct 2018, accepted on 26 Nov 2018 and first published on 26 Nov 2018


Article type: Paper
DOI: 10.1039/C8CP06160B
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Ab initio quantum–chemical computations of the absorption cross sections in HgX2 and HgXY (X,Y=Cl, Br, and I): Molecules of interest on the Earth’s atmosphere

    S. Sitkiewicz, D. Rivero, J. M. Oliva, A. Saiz-Lopez and D. Roca-Sanjuán, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP06160B

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