Renner-Teller and spin-orbit vibronic coupling effects in linear triatomic molecules with a half-filled pi shell

Area of Science:

• Theoretical Chemistry
• Molecular Physics
• Quantum Chemistry

Background:

• Understanding electronic state interactions is crucial for molecular spectroscopy and dynamics.
• Linear triatomic molecules with half-filled pi orbitals exhibit complex vibronic and spin-orbit couplings.
• Previous studies often employed simplified spin-orbit coupling operators, potentially missing key interactions.

Purpose of the Study:

• To investigate the vibronic and spin-orbit-induced interactions among specific electronic states ((3)Sigma(-), (1)Delta, (1)Sigma(+)) in linear triatomic molecules.
• To derive and analyze a comprehensive Hamiltonian matrix incorporating microscopic spin-orbit coupling.
• To elucidate the influence of these interactions on molecular potential energy surfaces and spin-vibronic energy levels.

Main Methods:

• Development of a 6x6 Hamiltonian matrix in a diabatic spin-orbital electronic basis set.
• Inclusion of terms up to fourth order in the molecular Hamiltonian expansion for bending normal coordinates.
• Analysis of symmetry properties and comparison of microscopic vs. phenomenological spin-orbit coupling operators.

Main Results:

• Identification of nonrelativistic Renner-Teller vibronic coupling within the (1)Delta state and between (1)Sigma(+) and (1)Delta states.
• Discovery of zeroth, first, and third-order vibronic coupling terms originating from microscopic spin-orbit interactions.
• Demonstration that these higher-order spin-orbit terms are absent when using phenomenological operators.

Conclusions:

• The microscopic spin-orbit coupling operator reveals significant vibronic coupling terms not captured by simpler models.
• These spin-orbit-induced vibronic interactions play a crucial role in shaping the adiabatic potential energy surfaces.
• Accurate prediction of spin-vibronic energy levels requires the inclusion of these detailed microscopic interactions.