Polyatomic ab Initio Complex Potential Energy Surfaces: Illustration of Ultracold Collisions

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Atomic and Molecular Collisions

Background:

• Resonances are metastable states crucial in physical processes, including observed autoionization in cold collision experiments.
• Theoretical analysis of autoionization relies on complex potential energy surfaces (CPESs), but ab initio calculations for polyatomic systems are challenging and scarce.

Purpose of the Study:

• To present a novel ab initio method for calculating polyatomic complex potential energy surfaces (CPESs).
• To interpret the autoionization process observed in He(2^3S) + H2 collisions using the developed CPES.
• To generate first-principles reaction rates for He collisions with ortho- and para-H2.

Main Methods:

• Development and application of a new computational approach for ab initio polyatomic CPES calculations.
• Analysis of the calculated CPES to determine the nature of the autoionization process.
• Utilizing the CPES to compute reaction rates from first principles.

Main Results:

• Successfully computed an ab initio polyatomic CPES, making such calculations feasible.
• The CPES provided a clear interpretation of the autoionization process in He(2^3S) + H2 collisions.
• Generated reaction rates showed excellent agreement with cold collision experimental measurements.

Conclusions:

• The developed method for calculating CPESs is robust and accurate.
• This computational tool aids in designing and interpreting experiments involving resonance states.
• The findings have implications for understanding processes like nucleobase damage and interatomic Coulombic decay.