An Analysis of Higher Order Vibration-Torsion-Rotation Interactions and Spectra for a Molecule with an Internal Rotor

Area of Science:

• Molecular Spectroscopy
• Quantum Chemistry
• Computational Physics

Background:

• Accurate analysis of molecular spectra requires precise Hamiltonian models.
• Understanding internal rotation and its interactions is crucial for interpreting molecular behavior.

Purpose of the Study:

• To develop a new ordering scheme for analyzing vibration-torsion-rotation (VTR) interactions.
• To investigate the magnitude of Hamiltonian terms in molecules with internal rotation.
• To assess the utility of a reduced Hamiltonian for fitting spectroscopic data.

Main Methods:

• Application of the contact transformation technique to the VTR Hamiltonian.
• Development of a new magnitude-based ordering scheme for VTR interactions.
• Fitting of microwave spectral lines using a reduced torsion-rotation Hamiltonian.

Main Results:

• A new scheme for ordering VTR interactions emphasizes the significance of torsional effects.
• The developed formulas enable clear analysis of higher-order VTR interactions in molecular spectra.
• A reduced torsion-rotation Hamiltonian was successfully applied to fit 568 microwave lines of CH318OH with high accuracy (rms of 0.262 MHz).

Conclusions:

• The proposed ordering scheme provides a systematic approach to analyze complex VTR interactions.
• The reduced Hamiltonian effectively fits experimental spectroscopic data, approaching experimental uncertainties.
• This work advances the understanding and analysis of internal rotation in molecules.