High-precision cavity-enhanced spectroscopy for studying the H₂-Ar collisions and interactions

Area of Science:

• Molecular spectroscopy
• Quantum chemistry
• Intermolecular forces

Background:

• Molecular collision dynamics influence spectral line shapes.
• Simple systems like H2-Ar are ideal for studying these interactions.
• Accurate potential energy surfaces (PES) are crucial for theoretical modeling.

Purpose of the Study:

• To investigate the H2-Ar system using high-accuracy spectroscopy and ab initio calculations.
• To validate the PES and quantum-scattering methodology.
• To understand the factors affecting collisional shift accuracy.

Main Methods:

• Cavity-ring-down spectroscopy to record collision-perturbed spectral line shapes.
• Ab initio quantum-scattering calculations on an accurate H2-Ar PES.
• Experimental measurements under conditions minimizing velocity-changing collision effects.

Main Results:

• Theoretical line shapes match experimental spectra at the percent level.
• Collisional shift prediction shows a 20% deviation from experimental values.
• Inaccuracies in the PES were identified as the primary source of error in collisional shift prediction.

Conclusions:

• The potential energy surface is the dominant factor limiting collisional shift accuracy.
• Approximate treatment of centrifugal distortion is sufficient for percent-level accuracy in collisional spectra.
• Methodology for studying molecular interactions via spectral line shapes is validated.