Vibronic origin of nonplanarity and puckered ring structure of tropylium trication (C7H7)3+
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GORINCHOY, Natalia, BALAN, Iolanta. Vibronic origin of nonplanarity and puckered ring structure of tropylium trication (C7H7)3+. In: Achievements and perspectives of modern chemistry, 9-11 octombrie 2019, Chişinău. Chisinau, Republic of Moldova: Tipografia Academiei de Ştiinţe a Moldovei, 2019, p. 74. ISBN 978-9975-62-428-2.
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Achievements and perspectives of modern chemistry 2019
Conferința "International Conference "Achievements and perspectives of modern chemistry""
Chişinău, Moldova, 9-11 octombrie 2019

Vibronic origin of nonplanarity and puckered ring structure of tropylium trication (C7H7)3+


Pag. 74-74

Gorinchoy Natalia, Balan Iolanta
 
Institute of Chemistry
 
Disponibil în IBN: 4 noiembrie 2019


Rezumat

Both the planar and pyramidal nuclear configurations of tropylium trication (C7H7)3+ are the metastable ones, and there exists a stable off-ring structure with a lower total energy [1]. In the present study, we have revealed the origin of the structural features of this molecule based on a detailed study of its electronic structure and the Jahn-Teller Effect (JTE) and the Pseudo JTE (PJTE). We start with two reference configurations, the planar structure of the D7h symmetry, and the pyramidal one of C6v symmetry. The planar D7h structure has a doubly degenerate ground electronic state 1E2' (the highest molecular orbital e1'' is occupied by two electrons). Therefore, due to the JTE, it undergoes the in-plane distortions to the structure of C2v symmetry. The crosssection of the adiabatic potential energy surfaces (APES) along the Qe2' coordinate is shown in the Figure 1, part (a). In its turn, this configuration is unstable with respect to the out-of-plane distortion of b1 symmetry due to the PJTE coupling of the ground 1A1 and the excited 1B1 electronic states (the PJTE (1A1+1B1) ob1 problem; part (b) in the Figure 1).Transformation of the pyramidal (C6v) structure into the equilibrium puckered ring structure takes place along the low-symmetry coordinate Qe1. At Qe1=0 the electronic ground state is 1A1, and there is a double-degenerate excited 1E1 state at 8.40 eV. Along the Qe1=/0 the C6v symmetry is reduced to Cs, the 1E1 doublet splits into the 1A'and 1A'' states, and one of its components (1A') has an avoided crossing with the ground 1A] state at Qe1= 2.44Å (part (c) in the Figre 1). The global minimum at Qe1=3.34 Å is a clear continuation of the split excited 1E1 term and corresponds to the equilibrium puckered ring structure. Thus, the metastability of the pyramidal configuration of tropylium trication molecule, and its equilibrium puckered ring structure are owing to the common action of the PJT coupling of the ground and excited electronic terms and the JT effect in the degenerate excited state.