Classical trajectory calculations for state-resolved Penning ionisation reactions of polycyclic aromatic hydrocarbon C₁₀H₈ in collision with He*(2³S)

ABSTRACT

The reaction dynamics of Penning ionisation of a polycyclic aromatic hydrocarbon (PAH), naphthalene C₁₀H₈, in collision with the metastable He*(2³S) atom is studied by classical trajectory calculations using an approximate interaction potential energy surface between He* and the molecule, which is constructed based on ab initio calculations for the isovalent Li + C₁₀H₈ system. The ionisation width (rate) around the molecular surface are obtained from overlap integrals of the He 1s orbital and the molecular orbital. The calculated collision energy dependences of partial Penning ionisation cross sections (CEDPICS) in the range 50–500 meV at 300 K have reproduced the experimental results semi-quantitatively. The opacity functions, which represent the reaction probability with respect to the impact parameter b, are discussed in connection with collision energy, interaction with He* and the exterior electron density of molecular orbitals. They indicate that the collisional ionisations of C₁₀H₈ can be classified into three types: π electron ionisations with negative collision energy dependences which are predominantly determined by attractive interaction with He*; σ orbitals ionisations of the hardcore type; σ orbital ionisations which reflect interaction potentials around CH bonds. The critical impact parameters b_c become larger with increasing collision energy due to the centrifugal barrier.

GRAPHICAL ABSTRACT

KEYWORDS:

• Trajectory calculation
• polycyclic aromatic hydrocarbons
• Penning ionisation
• reaction dynamics
• collision

Acknowledgements

The authors thank Professor Koichi Ohno and Professor Masakazu Yamazaki for providing their programme codes for trajectory calculations and helpful discussion. The quantum chemical calculations were performed on the computing servers in the Research Center for Computational Science, Okazaki, Japan.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Yoshihiro Yamakita http://orcid.org/0000-0002-2913-7516

Additional information

Funding

This work was financially supported by the Japan Society for the Promotion of Science under Kakenhi [grant number JP16K05645]; and the Institute for Quantum Chemical Exploration [H27Josei004] under a Research Grants-in-Aids.