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On the valence shell spectroscopy of 1,2-dichlorobenzene
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Resumo(s)
We report high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of 1,2-dichlorobenzene in the photon energy range 4.0–10.8 eV (310–115 nm). The electronic state spectroscopy of ortho-C6H4Cl2 has been investigated together with quantum chemical calculations at different levels of theory, also providing vertical excitation energies and oscillator strengths. The valence, mixed valence-Rydberg and Rydberg character of the electronic transitions is accompanied by fine structure which has been mainly assigned to in-plane breathing with C–Cl stretching, v7′a1, ring breathing and C–C stretching, v8′a1, in-plane ring breathing, v9′a1, C–Cl symmetric stretching, v10′a1, and in-plane C–Cl bending v11′a1 modes. The experimental absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of 1,2-dichlorobenzene in the Earth's atmosphere (0–50 km), showing that solar photolysis is expected to be a weak sink at altitudes lower than 20 km relative to [rad]OH radical reactions. Potential energy curves for the lowest-lying excited electronic states, as a function of the C–Cl stretching and in-plane C–Cl bending coordinates, were also obtained employing the time dependent density functional theory (TD-DFT) method. The results show the importance of the complex quasi-degenerate nature of the lowest-lying electronic states which in the intricate nuclear dynamics of the reaction coordinates, yield relevant internal conversion from Rydberg to valence character and in the asymptotic limit bond excision.
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Funding Information:
MHFB acknowledges the Brazilian agency Coordenaç˜ ao de Aperfei çoamento de Pessoal de Nível Superior (CAPES) and together with LVSD and ASB the support from the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). LVSD, ASB and MHFB also acknowledge Prof. Carlos A. M. de Carvalho for computational support at LFTC-DFis-UFPR and at LCPAD-UFPR. The authors wish to acknowledge the beam time at the ISA synchrotron, Aarhus University, Denmark. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. PLV acknowledges the Portuguese National Funding Agency (FCT) through research grant CEFITEC (UIDB/00068/2020), his visiting professor position at Federal University of Paraná, Curitiba, Brazil and the support from CAPES PrInt/UFPR. This work was also supported by Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, PD/00193/2012) and UCIBIO (UIDB/04378/2020).
Palavras-chave
1,2-dichlorobenzene Cross-sections Spectroscopy Theoretical calculations