Jahn-Teller effect in CH2DO∕CHD2O(X̃(2)E): vibronic coupling of all vibrational modes

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Computational Chemistry

Background:

• The Jahn-Teller effect influences molecular symmetry and electronic states.
• Methoxy radicals (CH3O) exhibit Jahn-Teller activity, particularly in their degenerate electronic states.
• Isotopologues like CH2DO and CHD2O show enhanced Jahn-Teller activity due to symmetry breaking in vibrational modes.

Purpose of the Study:

• To perform ab initio calculations of spin-vibronic energy levels for CH3O, CD3O, CH2DO, and CHD2O isotopologues.
• To investigate the splitting of energy levels caused by Jahn-Teller and spin-orbit interactions.
• To validate computational methods against experimental observations.

Main Methods:

• Utilized a diabatic model for calculating spin-vibronic energy levels.
• Adiabatic potential energy surfaces (APESs) were computed using high-level ab initio methods (UCCSD(T)-F12a/cc-pVQ(T)Z-F12a).
• Vibronic parameters were determined via least-squares fitting and the Duschinsky rotation method.

Main Results:

• Calculated spin-vibronic energy splittings for the vibrational ground states of CH3O, CH2DO, CHD2O, and CD3O were 61.8, 73.5, 70.2, and 54.5 cm⁻¹, respectively.
• Demonstrated that all vibrational modes in CH2DO/CHD2O are Jahn-Teller active, leading to energy level splitting.
• Observed good agreement between calculated splittings and available experimental results.

Conclusions:

• The study successfully models the complex spin-vibronic interactions in methoxy radical isotopologues.
• The theoretical framework accurately predicts energy level splittings arising from Jahn-Teller and spin-orbit couplings.
• Computational results provide valuable insights for interpreting experimental spectroscopic data.