Exploring molecular formation and growth upon ionization of van der Waals clusters using ab-initio molecular dynamics

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium (ISM)¹. The mechanism for their formation in the ISM's low-temperature environment is, as of yet, nonetheless a mystery. Understanding the growth mechanism of complex molecules such as PAHs and nitrogen-based PAHs (PAHN) is a long-standing challenge that has been drawing much attention for several decades.
Formation of the building blocks of PAHs and PAHNs upon ionization of van der Waals clusters will be presented. Results on small (up to 6 acetylene/HCN units) van der Waals clusters indicate that, since the clusters possess a large amount of extra energy after ionization, rich chemistry can occur^2,3. For example, after ionization, structures on the C₆H₆⁺ potential energy surface (PES) are accessible without barriers. Moreover, the formation of the basic building block of PAHs, namely the benzene cation, has been demonstrated using ab-initio molecular dynamics. The presence of spectator molecules has been proven to change the PES and partake a catalytic role in forming complex molecules^2,3.
1. Ehrenfreund, P. et al. , Farad. Discuss. 2006, 133 (0), 277-288.
2. Stein, T. et al., Proc Natl Acad Sci U S A 2017, 114 (21), E4125-E4133.
3. Stein* T. et al., PCCP, 22 (36), 20337, (2020).