Silane radical cation: a theoretical account on the Jahn-Teller effect at a triple degeneracy.

An ab initio quantum dynamics study is performed to examine the complex nuclear motion underlying the first photoelectron band of the silane molecule due to Jahn-Teller distortion via T2⊗(e+t2+t2) coupling. The problem is investigated by employing a quadratic vibronic coupling model for the Hamiltonian. All sheets of the required potential energy surface are established through extensive electronic structure calculations using the multireference configuration-interaction method. They cover at most two dimensions of the full 9D coordinate space, with the parameters defining the model Hamiltonian being determined by a least-squares fitting procedure. The results are compared with the available experimental data and discussed in relation to those obtained for the methane radical cation. The quadratic couplings of Jahn-Teller active vibrational modes are found to have a crucial role on the irregular vibronic structure, intensity of the spectral excitations, and overall width of the first photoelectron band of the title molecule. The impact of large amplitude motions on the vibronic structure and dynamics of the first photoelectron band has also been examined by varying their linear coupling parameters up to ±10%.