Key spectroscopic features of pyrazine lowest-lying 1B1u and 1B2u states

Dalagnol, L. V. S.; Bandeira, E.; Jones, N. C.; Hoffmann, S. V.; Bettega, M. H. F.; Limão-Vieira, P.

http://hdl.handle.net/10362/187127

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We report new spectral assignments from a high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of pyrazine (C4H4N2) lowest-lying valence excitations 1B1u1←X∼Ag1 and 1B2u1←X∼Ag1 in the photon energy range 3.7–6.2 eV (330–200 nm). The electronic state spectroscopy of C4H4N2 has been investigated together with quantum chemical calculations at the time-dependant density functional theory (TD-DFT) providing vertical excitation energies and oscillator strengths. The vibronic excitation in the 1B1u and 1B2u states is accompanied by fine structure assigned to C–H stretching, v1′ag, C–C stretching, v2′ag, C–H bending, v3′ag, ring breathing, v4′ag, and ring deformation v5′ag modes. Harmonic frequencies for pyrazine neutral electronic ground- and first excited-states have been obtained at the B3LYP/aug-cc-pVTZ level of theory. Absolute photoabsorption cross-section values are also reported from 3.7 up to 10.8 eV (310–113 nm) and compared with previous data in the literature.

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Funding Information: LVSD, EB and MHFB acknowledge the support from the Brazilian agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). LVSD, EB and MHFB also acknowledge Prof. Carlos A. M. de Carvalho for computational support at LFTC-DFis-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 (UID/00068) and his visiting professor position at Federal University of Paraná, Curitiba, Brazil.