Quantum Dynamics of the Vibrations of Helium Bound to the Nanosurface of a Large Planar Organic Molecule: Phthalocyanine·He van der Waals Complex

Abstract

We report rigorous quantum three-dimensional calculations of highly excited intermolecular vibrational states of the van der Waals (vdW) complex phthalocyanine.He (Pc.He). The Pc molecule was treated as rigid and the intermolecular potential energy surface (IPES) was represented as a sum of atom-atom Lennard-Jones pair potentials. The IPES has four equivalent global minima on the diagonals of the square-shaped Pc, inside its five-membered rings, and four slightly shallower local minima between them, creating a distinctive corrugation pattern of the molecular nanosurface. The vdW vibrational states analyzed in this work extend to about two-thirds of the well depth of the IPES. For the assignment of the in-plane (xy) vdW vibrational excitations it was necessary to resort to two sets of quantum numbers, the Cartesian quantum numbers [nu(x), nu(y)] and the quantum numbers (v, l) of the 2D isotropic oscillator, depending on the nodal structure and the symmetry of the wave functions. The delocalization of the He atom parallel to the molecular surface is large already in the ground vdW state. It increases rapidly with the number of quanta in the in-plane vdW vibrations, with the maximum root-mean-square amplitudes Deltax and Deltay of about 7 au at the excitation energies around 40 cm(-1). The wave functions of the highly excited states tend to be delocalized over the entire nanosurface and often have a square shape, reflecting that of the substrate.

Structures, Energetics, and Dynamics of Helium Adsorbed on Isolated Fullerene Ions

“…At the other end of the spectrum that started with graphitic surfaces are helium layers physisorbed on isolated nanotubes [10], planar aromatic molecules [11], and fullerenes [12,13]. The dimensionality of their surfaces changes from 0D or 1D to 2D as the size of the system increases.…”

“…The dimensionality of their surfaces changes from 0D or 1D to 2D as the size of the system increases. The resonance frequency of a single-walled suspended nanotube has been measured to monitor phase transitions in an adsorbate of argon and xenon [10]; the coupling of helium to gas-phase anthracene, phtalocyanine, and other planar aromatic molecules has been probed by high-resolution spectroscopy (see references in [11]). …”

Gas‐Phase Electronic Structure of Phthalocyanine Ions: A Study of Symmetry and Solvation Effects

“…Spectroscopic investigations of H 2 Pc and its derivatives have been carried out in various environments, including surfaces, [ 8 ] solutions [ 9 ] or molecular matrices. [ 10 ] A range of techniques has been employed, including Raman spectroscopy, [ 9a ] UV–vis absorption spectroscopy, [ 10 , 11 ] (FT)IR spectroscopy, [ 11 , 12 ] and fluorescence spectroscopy.…”

Ab Initio Potentials for the Ground S0 and the First Electronically Excited Singlet S1 States of Benzene–Helium with Application to Tunneling Intermolecular Vibrational States

“…Furthermore, a study of the impact of the rotation of a benzene molecule on the helium density distribution in a helium droplet was conducted in ref . In a bunch of theoretical studies, the vibrational dynamics of He in ArmHe complexes, including large PAH molecules up to pentacene, was investigated. − ,− In all of these studies, the potential energy surface (PES) was obtained using simple atom–atom Lennard-Jones semiempirical potentials. − In some cases, these potentials were adjusted to reproduce experimental data, but the accuracy of the potentials should be confirmed by more reliable PESs based on ab initio calculations. It is possible that such potentials may differ significantly from ab initio potentials and inaccurately reproduce experimental results like it takes place for BzKr …”