Testing Lineshape Models: Measurements for v = 1-0 CO Broadened by He and Ar

Area of Science:

• Spectroscopy
• Molecular Physics
• Quantum Optics

Background:

• Understanding spectral line shapes is crucial for molecular physics and atmospheric science.
• Existing semi-classical models often struggle to fully capture complex molecular interactions and line broadening phenomena.

Purpose of the Study:

• To investigate the spectral profiles of P and R branch lines in carbon monoxide (CO) gas mixtures with helium (He) and argon (Ar).
• To evaluate the performance of various semi-classical models, including those accounting for speed-dependent effects, in describing the observed lineshapes.
• To analyze the impact of speed dependence on Dicke narrowing and its relation to the rotational quantum number.

Main Methods:

• Experimental measurement of spectral profiles for CO-He and CO-Ar mixtures at 301.5 K.
• Comparison of experimental data with several semi-classical models, focusing on speed-dependent translational motion and optical coherence relaxation.
• Application of a correlated speed-dependent Galatry model (Ciurylo-Szudy).

Main Results:

• Observed spectral profiles of numerous P and R branch lines in CO-He and CO-Ar mixtures.
• The correlated speed-dependent Galatry model demonstrated an apparent reduction in Dicke narrowing, reaching up to 100% in certain cases.
• This reduction showed a strong dependence on the rotational quantum number.

Conclusions:

• While models can fit experimental data, no single model is entirely satisfactory, indicating limitations in current theoretical approaches.
• The study highlights the significant role of speed-dependent effects in spectral line shapes, particularly concerning Dicke narrowing.
• Further refinement of theoretical models is needed to accurately describe molecular spectral profiles.