VIBRATIONAL DEPENDENCE OF LINE COUPLING AND LINE MIXING IN SELF-BROADENED PARALLEL BANDS OF NH₃

Area of Science:

• Molecular Spectroscopy
• Atmospheric Physics
• Quantum Chemistry

Background:

• Ammonia (NH3) exhibits complex spectral line shapes due to various molecular interactions.
• The v2 mode excitation in NH3 leads to significant inversion splitting, influencing spectral properties.
• Line coupling and line mixing are crucial for accurate spectroscopic analysis, particularly in atmospheric applications.

Purpose of the Study:

• To investigate the influence of inversion splitting on line coupling and line mixing effects in self-broadened NH3 lines.
• To calculate and analyze line-shape parameters for parallel bands involving the excited v2 mode of NH3.
• To compare calculated spectral parameters with experimental data and existing databases like HITRAN 2012.

Main Methods:

• Theoretical calculation of line coupling and line mixing effects for self-broadened NH3 lines.
• Analysis of the v2 dependence of inversion splitting on spectral line-shape parameters.
• Calculation of self-broadened half-widths for v2 and 2v2 bands.

Main Results:

• The v2 dependence of inversion splitting plays a dominant role in line-shape parameters.
• Intra-doublet and inter-doublet couplings diminish or disappear with increasing v2 quantum numbers and associated splitting.
• Calculated half-widths show good agreement with measurements but poor agreement with HITRAN 2012 data, suggesting a need for database updates.

Conclusions:

• Inversion splitting is a key factor determining line coupling and mixing in excited NH3 bands.
• The current formalism accurately explains line mixing in the v1 band but shows discrepancies for v2 and 2v2 bands, necessitating new measurements.
• HITRAN 2012 data for NH3 requires updates, particularly concerning empirical formulas used for spectral parameter prediction.