Stereodynamical control of cold HD + D₂ collisions.

Area of Science:

• Physical Chemistry
• Quantum Dynamics
• Molecular Collisions

Background:

• Experimental studies using Stark-induced adiabatic Raman passage (SARP) probed stereodynamic control in HD(v=1, j=2) + D2 collisions.
• Previous analysis focused on specific rotational transitions in HD, potentially overlooking dominant inelastic channels.

Purpose of the Study:

• To perform full-dimensional quantum calculations of stereodynamic control in HD + D2 collisions.
• To investigate rotational quenching and excitation dynamics.
• To compare theoretical predictions with experimental results, particularly SARP experiments.

Main Methods:

• Full-dimensional quantum scattering calculations were performed using two accurate H4 potential energy surfaces.
• Analysis focused on rotational transitions in HD and D2 molecules during collisions.

Main Results:

• Rotational quenching of HD concurrent with D2 rotational excitation was found to be the dominant inelastic transition for both potential surfaces.
• This dominant channel has cross sections four times larger than elastic scattering for the same HD quenching transition.
• Resonances (l=3 for ortho-D2, l=1 and l=3 for para-D2) were observed in the cross sections.

Conclusions:

• The dominant inelastic process in HD + D2 collisions involves concurrent rotational quenching of HD and excitation of D2, a channel not fully considered in prior SARP experiment analysis.
• Theoretical calculations show excellent agreement with elastic and inelastic differential cross sections but less satisfactory agreement with SARP experiments for specific transitions.
• The findings suggest a re-evaluation of the interpretation of SARP experiments concerning the dominant inelastic pathways in these molecular collisions.