Spin-orbit vibronic coupling in Π4 states of linear triatomic molecules

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Theoretical Chemistry

Background:

• The Renner effect describes vibronic coupling in linear molecules.
• Spin-orbit coupling significantly influences electronic states.

Purpose of the Study:

• To analyze the Renner vibronic-coupling problem in 4Π electronic states of linear molecules.
• To rigorously include spin-orbit coupling in the analysis.

Main Methods:

• Construction of an 8x8 Hamiltonian matrix for the 4Π state in a diabatic representation.
• Taylor expansion of the Hamiltonian in the bending normal mode up to second order.
• Inclusion of spin-orbit coupling effects.

Main Results:

• Identified SO-induced vibronic-coupling terms linear in bending amplitude, alongside quadratic electrostatic Renner coupling.
• Investigated the influence of linear and quadratic Renner coupling on four Kramers-degenerate potential energy surfaces.
• Analyzed spectroscopic effects of the linear SO-vibronic-coupling mechanism.

Conclusions:

• Spin-orbit coupling introduces linear vibronic-coupling terms in 4Π states, analogous to 2Π and 3Π states.
• These couplings significantly affect the potential energy surfaces and observable vibronic spectra.
• The findings provide insights into the spectroscopy of linear molecules with 4Π electronic states.