Non-adiabatic effects in the H₃⁺ spectrum

Area of Science:

• Quantum chemistry
• Molecular spectroscopy
• Theoretical chemistry

Background:

• Non-adiabatic coupling effects are crucial for accurate rovibrational energy level computations in molecular ions.
• Previous methods for calculating these energy shifts have limitations.

Purpose of the Study:

• To review strategies for obtaining non-adiabatic energy shifts.
• To introduce and apply a novel empirical method for calculating these shifts.
• To construct an accurate potential energy surface for D3+ and analyze its rovibrational frequencies.

Main Methods:

• Review of existing strategies for non-adiabatic energy shift calculations.
• Development and application of an empirical method using the stockholder atoms-in-molecules approach with effective vibrational reduced masses.
• Construction of a highly accurate potential energy surface for D3+, including relativistic and quantum electrodynamic terms.

Main Results:

• The non-adiabatic coupling effect is approximately 2 cm⁻¹ for H3+.
• The new empirical method provides a promising approach for calculating energy shifts.
• Accurate band origins for D3+ were obtained, improving upon existing data.

Conclusions:

• Non-adiabatic coupling must be included in high-accuracy calculations for H3+.
• The proposed method of effective vibrational reduced masses is effective for accounting for these effects.
• The study provides improved spectroscopic data for D3+.