Global analytical ab initio ground-state potential energy surface for the C((1)D)+H2 reactive system

Area of Science:

• Chemical Physics
• Quantum Chemistry
• Theoretical Chemistry

Background:

• The C((1)D) + H2 reaction is a key system for understanding chemical dynamics.
• Accurate potential energy surfaces are crucial for simulating reaction pathways and kinetics.
• Previous surfaces lacked detailed descriptions of conical intersections and van der Waals interactions.

Purpose of the Study:

• To construct a new global ab initio potential energy surface (ZMB-a) for the 1(1)A' state of the C((1)D)+H2 system.
• To accurately represent conical intersections and van der Waals interactions in the potential energy surface.
• To investigate reaction barriers and complex formation in the C((1)D)+H2 system.

Main Methods:

• Ab initio calculations using the internally contracted multireference configuration interaction (MRCI) approach.
• Utilized the aug-cc-pVQZ basis set for high accuracy.
• Employed many-body expansions with permutationally invariant polynomials for analytical fitting.

Main Results:

• Developed the ZMB-a global potential energy surface for C((1)D)+H2.
• Identified two significant energy barriers due to conical intersections: 9.07 kcal/mol (H-CH dissociation) and 12.39 kcal/mol (collinear C((1)D) attack).
• The surface accurately reproduces van der Waals interactions, predicting linear C-HH and CH-H/HC-H van der Waals complexes.

Conclusions:

• The ZMB-a surface provides a more accurate representation of the C((1)D)+H2 reaction dynamics, especially near conical intersections.
• The higher calculated barriers suggest a significant impact on reaction rates compared to previous theoretical models.
• The inclusion of detailed van der Waals interactions offers insights into intermediate complex formation.