Computational and experimental investigation of intermolecular states and forces in the benzene–helium van der Waals complex

Abstract

A study of the intermolecular potential-energy surface ͑IPS͒ and the intermolecular states of the perprotonated and perdeuterated benzene-He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two-to four-body atom-atom terms is obtained. This IPS, and two other Lennard-Jones atom-atom surfaces from the literature, are each employed in dynamically exact ͑within the rigid-monomer approximation͒ calculations of Jϭ0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational transitions are also calculated for each of the three surfaces. The calculated results are compared with experimental results reported herein pertaining to intermolecular Raman spectra of benzene-He. The calculated rotational constants are compared with experimental values from the literature. The fitted IPS of this work leads to calculated observables that match the experimental results very well. The IPSs from the literature are not as successful, specifically in regard to the intermolecular Raman spectra.

Infrared spectroscopic and ab-initio studies of the benzene dimer

“…The neon atoms thus effectively acts as a catalyst for the isomerization in the benzene dimer, forming selectively the low energy isomer (C 6 H 6 ) S (C 6 D 6 ) T . This mechanism, in combination with calculated energies [7,9], also predicts that the parallel displaced sandwich isomer should not survive in the molecular beam, as already helium would catalyse its destruction.…”

“…This is exactly what can happen when a benzene dimer collides with a neon atom. As an estimate for the internal energy of the benzene dimer-rare gas complex, the binding energy D 0 of a rare gas atom to the benzene monomer molecule can be taken, which is about 48 cm −1 [7] and 120 cm −1 [8] for helium and neon, respectively. A transient complex of the benzene dimer with neon thus has enough energy for the exchange of the monomer units while a complex with helium has not.…”

Infrared spectra of Rg1,2-C6H6 complexes, Rg = He, Ne, Ar

“…Their analysis yielded ground state B-values of 0.1220 and 0.0876 cm -1 for the dimer and trimer, respectively, which resulted in intermolecular distances of r 0 = 3.602 or 3.596 Å (these are for the distance between the He atom(s) and the benzene plane). A detailed ab initio potential surface for He-C 6 H 6 has been reported by Lee et al [10], together with nonlinear Raman spectra of some intermolecular vibrations…”

“…There is an extensive history of spectroscopic studies of weakly-bound rare gas (Rg)benzene clusters [1], ranging from microwave to ultraviolet wavelength regions, and including techniques such as Fourier transform microwave, laser induced fluorescence, coherent ion dip, resonant enhanced two photon ionization, and nonlinear Raman spectroscopies [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Rg -benzene dimers have simple structures with the rare gas atom localized on the C 6 symmetry axis at a distance of about r 0 = 3.4 -3.8 Å (depending on the Rg) from the plane of the benzene molecule.…”

Iterative Methods for Computing Vibrational Spectra

“…Although direct product bases are huge, they can be used by exploiting the structure of the basis to efficiently evaluate the MVPs required to use iterative methods. The Lanczos and filter diagonalisation methods are popular iterative methods for solving the time-independent Schroedinger equation [40][41][42][43][44][45][46][47]. For a molecule with as many as five atoms, they make it possible, even with a direct product basis, to solve the vibrational Schroedinger equation with a general PES.…”