Pseudo Jahn-Teller Origin of Instability of Planar Configuration in C2H4 Radical Anion: JT Vibronic Coupling

The structural and electronic characteristics of both C2H4 and C2H4− compounds wereidentified as planar molecule with D2h point group that studied theoretically using Hartree –Fock(HF)/Def2-TZVPP method. Following this work, the Time Dependent-DFT (TD-DFT) andNatural Bond Orbital analysis (NBO) were performed by Gaussian 09 program suites [1].Optimized structure C2H4 is a structure with 1A1g ground state, in contrary C2H4− optimized with 2B2g,has two imaginary frequencies (distortion modes, i.e., Qb2g and Qb3u) which each of distortionmodes creates C2h (Trans-bent) and C2v (Cis-bent) structures, respectively. It is found that theC2H4− D2h symmetry is broken and the distortion was carried out by the pseudo Jahn-Teller effect(PJTE). Based on calculation results, C2H4− transformed from unstable planar configuration withD2h symmetry to a C2h symmetry stable geometry. The vibronic coupling interaction betweenground (2B2g) and excited (2A1g) states by [(B2g+A1g) ⊗ b2g] is the reason the breaking symmetry.The donor-acceptor (bond, anti-bond) NBO analysis interactions showed that the stabilization energies E(2) associated with electron delocalization. The occupancy of the orbitals, the bonding order, theoff-diagonal element of the matrix F (i, j), deviation of the orbital C= C, and hybrid (spn)parameters are compared for D2h and C2h geometries. Finally, the canonical molecular orbitals(CMO) analysis is used to determine the characteristics, components and contribution of HOMOand LUMO orbitals in wave functions [2].

کلیدواژه ها:

Symmetry Breaking ، Imaginary Frequencies ، Trans-Bent Configuration ، Pseudo Jahn-Teller Effect ، JT Vibronic Coupling and Natural Bond Orbital