Capturing the Elusive Water Trimer from the Stepwise Growth of Water on the Surface of the Polycyclic Aromatic Hydrocarbon Acenaphthene

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are key players in reaction chemistry. While it is postulated that they serve as a basis for ice grains, there has been no direct detection of PAHs in astronomical environments. We aim to investigate the hydration of PAHs to set a foundation for the future exploration of potential ice formation pathways. We report results from chirped pulse Fourier transform microwave spectroscopy and quantum-chemical calculations for the PAH acenaphthene and acenaphthene complexed with up to four water molecules. The acenaphthene-(HO) complex is of particular interest as the elusive cyclic water trimer was observed. It appears in a slightly distorted configuration when compared with the pure water trimer. This is explained by hydrogen-bond net cooperativity effects. Binding energies for the complexes are presented. Our results provide insight into the onset of complex aggregation that could be occurring in extraterrestrial environments as part of ice grain formation.

The Unexplored World of Cycloalkene–Water Complexes: Primary and Assisting Interactions Unraveled by Experimental and Computational Spectroscopy

“…Some alkyne complexes with water [14] and alcohols [15] have indeed been studied, together with complexes of phenol with ethylene and acetylene [16] as well as of tert-butyl alcohol with bulky alkenes. [17] However,if one excludes the molecular complexes involving aromatic systems as the p-partner in the interaction, [18][19][20][21] olefinic···HÀ Oc ontacts remain surprisingly unexplored, with ethylenewater and ethylene-methanol being, to the best of our knowledge,t he only clusters well characterized. [22,23] In Ref.…”

“…[22,23] In Ref. [22],i twas demonstrated that the p-system of the C=C bond can act as aw eak proton acceptor,t hus leading to the formation of aweak hydrogen bond (wHB), asituation that is completely different from what is observed for aromatic compounds.I ndeed, in the case of benzene,w ater resides above the center of the ring, [18,19] while for molecules possessing more than one aromatic system, such as corannulene [20] and acenaphthene, [21] water binds to the partner molecules through two equivalent OÀH···p HBs.F ew alkane and cycloalkane···H 2 Oa dducts have also been character-ized [24] but very broad and shallow energy minima were observed in the absence of other stabilizing interactions.…”

The Unexplored World of Cycloalkene–Water Complexes: Primary and Assisting Interactions Unraveled by Experimental and Computational Spectroscopy

“…Some alkyne complexes with water and alcohols have indeed been studied, together with complexes of phenol with ethylene and acetylene as well as of tert ‐butyl alcohol with bulky alkenes . However, if one excludes the molecular complexes involving aromatic systems as the π‐partner in the interaction, olefinic⋅⋅⋅H−O contacts remain surprisingly unexplored, with ethylene–water and ethylene–methanol being, to the best of our knowledge, the only clusters well characterized . In Ref.…”

“…, it was demonstrated that the π‐system of the C=C bond can act as a weak proton acceptor, thus leading to the formation of a weak hydrogen bond (wHB), a situation that is completely different from what is observed for aromatic compounds. Indeed, in the case of benzene, water resides above the center of the ring, while for molecules possessing more than one aromatic system, such as corannulene and acenaphthene, water binds to the partner molecules through two equivalent O−H⋅⋅⋅π HBs. Few alkane and cycloalkane⋅⋅⋅H 2 O adducts have also been characterized but very broad and shallow energy minima were observed in the absence of other stabilizing interactions.…”

Water Docking Bias in [4]Helicene

“…[3,4] Prototypical clusters of small PA Hs with af ew water molecules provide simplified models to determine the initial steps of ice grain formation and infer chemical reactivity from the local environment. [3][4][5] Studies performed on non-centrosymmetric substrates are,h owever, yet poorly explored. Chiral PA Hs such as helicenes are good model systems to investigate the initial steps of ice grain evolution taking place in amedium intrinsically lacking acenter of symmetry.These scenarios are rich probes for symmetry-breaking events, leading to handedness biasing in space and homochirality.…”