Coupled-channel study of the Rydberg-valence interaction in HBr.

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Computational Physics

Background:

• Understanding the electronic structure of molecules like hydrogen bromide (HBr) is crucial for predicting their chemical and physical properties.
• Previous studies have identified valence and Rydberg states in HBr, but a comprehensive theoretical investigation including spin-orbit interactions was needed.

Purpose of the Study:

• To perform an ab initio study of the low-lying valence and Rydberg states of HBr.
• To accurately calculate vibrational levels and spectroscopic parameters for these states.
• To provide theoretical data for previously uncharacterized Rydberg states of HBr.

Main Methods:

• Utilized the multireference single- and double-excitation configuration interaction (MRD-CI) method.
• Incorporated spin-orbit interaction into the calculations.
• Employed a coupled-channel treatment for vibrational level calculations based on diabatic potentials.

Main Results:

• Identified two minima in the first excited adiabatic potential of ¹Σ⁺ symmetry, corresponding to the observed Rydberg E¹Σ⁺ and valence V¹Σ⁺ states.
• Successfully reproduced chaotic energy separations between observed vibrational levels.
• Generated novel theoretical data for numerous Rydberg states of HBr in the 66-79 × 10³ cm^-1 excitation energy range.

Conclusions:

• The theoretical calculations show good agreement with experimental data for spectroscopic parameters.
• The study provides a foundation for future research into radiative and non-radiative processes in HBr.
• This work advances the understanding of electronic structure and excited states in HBr.