Solvation of carbonaceous molecules by para-H2 and ortho-D2 clusters. I. Polycyclic aromatic hydrocarbons

Abstract

This work theoretically examines the progressive coating of planar polycyclic aromatic hydrocarbon (PAH) molecules ranging from benzene to circumcoronene (C54H18) by para-hydrogen and ortho-deuterium. The coarse-grained Silvera-Goldman potential has been extended to model the interactions between hydrogen molecules and individual atoms of the PAH and parametrized against quantum chemical calculations for benzene-H2. Path-integral molecular dynamics simulations at 2 K were performed for increasingly large amounts of hydrogen coating the PAH up to the first solvation shell and beyond. From the simulations, various properties were determined such as the size of the first shell and its thickness as well as the solvation energy. The degree of delocalization was notably quantified from an energy landscape perspective, by monitoring the fluctuations among inherent structures sampled by the trajectories. Our results generally demonstrate a high degree of localization owing to relatively strong interactions between hydrogen and the PAH, and qualitatively minor isotopic effects. In the limit of large hydrogen amounts, the shell size and solvation energy both follow approximate linear relations with the numbers of carbon and hydrogen in the PAH.

Adsorption of molecular hydrogen on coronene with a new potential energy surface

“…The present PIMC investigation has been also extended to (D 2 ) N -coronene clusters, for some selected values of N. Previous investigations 33 did not reveal significant qualitative differences between the isotopic variants D 2 and H 2 of these systems. Thus, distributions of minimum distances and solvation energies exhibited a similar trend for both types of clusters.…”

“…In particular, solvation energies for (ortho-D 2 ) N -coronene clusters were found more negative than those for (para-H 2 ) N -coronene for the entire range of different sizes considered in the PIMD study of Ref. 33 . The total energies calculated in our work with the PIMC method for (D 2 ) Ncoronene for N = 6, 7, 14, 16 and 38 are -197, -222.4, -379.5, -410 and -754 meV, respectively.…”

“…The present PES has been obtained under the assumption of a pseudoatom behavior for the molecular hydrogen. This is, on the other hand, the usual procedure followed in previous investigations on similar systems formed by H 2 on either molecules or surfaces 22,23,29,33,80,81 . Thus, for example, Špirko et al 29 neglected internal rotations of absorbed molecular hydrogen keeping an equilibrium orientation with a frozen H-H distance, and Nho et al assumed H 2 as spherical particles interacting via a semiempirical Silvera and Goldman potential 81 .…”

“…Most of the structural properties obtained on those calculations indicate that the relative orientation of the H 2 unit has little influence. The path integral molecular dynamics (PIMD) calculation by Calvo and Yurtsever 33 on H 2 -solvated PAH clusters employed a simplified potential energy surface (PES) in which H 2 internal degrees of freedom are neglected.…”

Isomeric Broadening of C60+ Electronic Excitation in Helium Droplets: Experiments Meet Theory

“…The PIMD methodology has been described in detail elsewhere 39,40 and will not be repeated here. A Trotter number of 128 was chosen at all temperatures with time steps of 5 fs (1 and 5 K) and 1 fs (10 K) and simulation times of 100 ps for equilibration and 500 ps for production runs.…”