Constructing potential energy surface for carbon-chain containing systems using the radial angular network with...

Area of Science:

• Chemical Physics
• Computational Chemistry
• Molecular Spectroscopy

Background:

• Accurate potential energy surfaces are crucial for understanding molecular excitation during collisions.
• Calculating these surfaces for carbon-chain molecules, such as cyanopolyynes, has been a significant challenge.
• This difficulty has limited the availability of rate coefficients for important collisional systems involving helium.

Purpose of the Study:

• To introduce a novel computational approach, the Radial Angular Network with Gradual Expansion (RANGE), for constructing analytical potential energy surfaces.
• To apply the RANGE method to cyanopollyne-helium complexes (HC3N-He, HC5N-He, HC7N-He).
• To investigate the propensity rules governing state changes in these collisional systems.

Main Methods:

• The Radial Angular Network with Gradual Expansion (RANGE) method was developed, integrating ab initio potential construction with analytical form determination.
• The HC3N-He system was used as a benchmark to validate the RANGE method's reliability.
• The RANGE approach was applied to derive analytical potentials for HC5N-He and HC7N-He.

Main Results:

• The RANGE method successfully constructed analytical potential energy surfaces for HC3N-He, HC5N-He, and HC7N-He.
• Analysis revealed systematic trends in the potentials: increasing anisotropy with carbon chain length, correlation between local minima number and carbon atoms, and a consistent shallow minimum near the dissociation limit.
• Quantum mechanical calculations indicated a propensity for Δj = 2 transitions in the collisional excitation of HC3N, HC5N, and HC7N by He.

Conclusions:

• The RANGE method provides a reliable and efficient approach for generating accurate analytical potential energy surfaces for complex molecular systems.
• The study establishes key trends in the interaction potentials of cyanopollyne-He complexes.
• A consistent propensity rule favoring Δj = 2 transitions was identified for the collisional excitation of these molecules by helium.