Renner-Teller and pseudo-Renner-Teller interactions in the electronic ground and excited states of the dicyanoacetylene radical cation: Assignment of vibronic spectrum and elucidation of nonradiative and radiative decay mechanisms

• Published in: Computational and theoretical chemistry Vol. 1155; pp. 109 - 124
• Main Authors: Ghosh, Arpita, Rajak, Karunamoy, Kanakati, Arun Kumar, Mahapatra, S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2019
• Subjects: dicyanoacetylene radical cation; Nonadiabatic quantum dynamics; Pseudo-Renner-Teller effect; Renner-Teller effect; dicyanoacetylene radical cation; Nonadiabatic quantum dynamics; Pseudo-Renner-Teller effect; Renner-Teller effect
• ISSN: 2210-271X
• DOI: 10.1016/j.comptc.2019.03.010

[Display omitted] •Vibronic coupling in the first five electronic states of symmetric linear dicyanoacetylene radical cation is studied in this paper.•Effect of both Renner-Teller and pseudo-Renner-Teller coupling of electronic states on the vibronic band structure, internal conversion dynamics and radiative decay of these five electronic states are examined at length.•The electronic potential energy surfaces and their coupling surfaces calculated with the aid of ab initio quantum chemistry methods and first principles nuclear dynamics calculations are carried out on the coupled manifold of electronic states.•The progressions in the vibronic band structure are identified, assigned and compared with the available experimental data.•The theoretical results are found to be in good accord with the experiment. Vibronic interactions in the first five energetically lowest electronic states (X̃2Πu-Ã2Σg+-B̃2Σu+-C̃2Πg-D̃2Πu) of dicyanoacetylene radical cation (C4N2·+) and their effect on the nuclear dynamics are examined in this article. The spectroscopy of C4N2·+ is a subject of outstanding complexity and addressed by the [see, the recent article, J. Chem. Phys. 139, 184304 (2013)]. The energetic ordering of electronic states and the emission mechanism of the states seem to have ambiguity. Here we have undertaken a detailed theoretical study in an attempt to resolve it. A vibronic coupling Hamiltonian of the five electronic states mentioned above is constructed in a diabatic electronic basis and with the aid of ab initio quantum chemistry calculations. Quantum nuclear dynamics studies are carried out by both time-independent and time-dependent quantum mechanical methods. The vibronic spectrum is calculated and the progressions are identified in terms of vibrational modes and compared with experimental slow photoelectron spectroscopy results. Renner-Teller (RT) coupling within the degenerate electronic states (X̃, C̃ and D̃) and the pseudo-Renner-Teller (PRT) coupling among states are examined in detail to elucidate their impact on the vibronic structure of the state and its decay mechanism to the ground (X̃) electronic state. While the dynamics of the X̃ and D̃ states is somewhat simple, the same of the Ã, B̃ and C̃ states is outstandingly complex due to strong RT and PRT interactions.