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The electronic states of 2-chlorotoluene in the 4.0–10.8 eV photon energy range
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Resumo(s)
Absolute cross-section values of 2-chlorotoluene are reported from vacuum ultraviolet photoabsorption measurements in the photon energy range 4.0–10.8 eV (310–115 nm), together with quantum chemical calculations. The nature of the electronic states is associated with transitions from the neutral ground state to valence, mixed valence-Rydberg and Rydberg orbitals. The fine structure in the photoabsorption bands has been mainly assigned to C–H stretching (CH3), v6′(a′), C–H in-plane bending, v16′(a′)/v17′(a′), C–Cl stretching, v21′(a′) and C–C in-plane bending v23′(a′) modes. The measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of 2-chlorotoluene in the upper stratosphere, showing that solar photolysis can only be a relevant sink at altitudes above 23 km. We have also performed calculations at the TD-DFT level to obtain optimised geometries, excitation energies, oscillator strengths and potential energy curves for the lowest-lying electronic excited states. Special attention is given to state-selective vibrational excitation to obtain information on the internal conversion mechanisms governing the nuclear dynamics in the photoabsorption regions where C=C stretching, C–H in-plane bending and C–Cl/C–CH3 stretching modes have been assigned. The results show a relevant internal conversion from Rydberg to valence character and vice-versa, dictating the nuclear dynamics of 2-chlorotoluene upon photon absorption.
Descrição
PASR acknowledges support from the Brazilian agency Coordenaç˜ao
de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). ASB and
MHFB acknowledge support from the Brazilian agency Conselho
Nacional de Desenvolvimento Científico e Tecnol´ogico (CNPq). PASR,
ASB and MHFB also acknowledge Prof. Carlos de Carvalho for compu-
tational 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 sup-
ported by the project CALIPSOplus under 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 Paran´a, Curitiba, Brazil and
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).
© 2024 The Author(s). Published by Elsevier B.V.
Palavras-chave
photolysis Excitation energy Excited states Rydberg states