Inelastic Collisions of O₂ with He at Low Temperatures

Area of Science:

• Chemical Physics
• Molecular Collisions
• Spectroscopy

Background:

• Understanding molecular collisions is crucial for chemical kinetics and fluid dynamics.
• Low-temperature environments are relevant to astrophysics and industrial processes.
• The rotational dynamics of oxygen molecules (O2) are complex due to electron spin.

Purpose of the Study:

• To experimentally investigate rotationally inelastic collisions between O2 and He.
• To determine state-to-state rate coefficients for O2:He collisions in the 10-34 K range.
• To validate a kinetic master equation (MEQ) for describing O2 rotational populations.

Main Methods:

• Utilizing supersonic gas jets of O2 and He mixtures.
• Employing Raman spectroscopy for probing rotational populations.
• Developing and applying a kinetic master equation (MEQ) model.

Main Results:

• Experimental measurements agree with the MEQ model for temperatures between 10 and 34 K.
• State-to-state rate coefficients for O2:He inelastic collisions were calculated.
• The influence of O2 fine structure on collision dynamics was analyzed.

Conclusions:

• The kinetic master equation accurately describes O2 rotational populations in O2:He supersonic jets.
• The study provides valuable state-to-state rate coefficients for O2:He collisions.
• Low-temperature collision dynamics of O2 are significantly influenced by electron spin fine structure.