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We describe variational calculations of J=0 intermolecular states in Br2–4HeN clusters. The method employed is analogous to configuration-interaction calculations in electronic-structure work and relies on the ability to express the intermolecular Hamiltonian H⁁v as a sum of one- and two-body terms. A basis set is built up from solutions to the Schrödinger equation in which only the one-body terms of H⁁v are included. These configurations are products of N=1 eigenstates. The matrix of H⁁v in a symmetry-adapted configuration basis is then computed, the two-body terms of H⁁v serving to couple different configurations. This computation involves integrals of dimension five or less. Filter diagonalization is then used to obtain energies and eigenfunctions within a selected energy range. Results on clusters having N=2–5 are reported. [ABSTRACT FROM AUTHOR]

We describe variational calculations of J=0 intermolecular states in Br2–4HeN clusters. The method employed is analogous to configuration-interaction calculations in electronic-structure work and relies on the ability to express the intermolecular Hamiltonian H⁁v as a sum of one- and two-body terms. A basis set is built up from solutions to the Schrödinger equation in which only the one-body terms of H⁁v are included. These configurations are products of N=1 eigenstates. The matrix of H⁁v in a symmetry-adapted configuration basis is then computed, the two-body terms of H⁁v serving to couple different configurations. This computation involves integrals of dimension five or less. Filter diagonalization is then used to obtain energies and eigenfunctions within a selected energy range. Results on clusters having N=2–5 are reported. [ABSTRACT FROM AUTHOR]

A study of the intermolecular potential-energy surface (IPS) 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 approximation) calculations of J=0 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. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents an approach toward the dynamically exact calculation of intermolecular states in molecule-large molecule complexes. Employment of an intermolecular Hamiltonian; Use of filter diagonalization techniques to diagonalize the Hamiltonian; Interpretation of the results of the calculation in terms of five internal rotation states.

The results of nonlinear Raman experiments on two intermolecular bands of expansion-cooled naphthalene trimer at 0.03 cm-1 resolution are reported. The polarization and intensity dependences of the observed band contours strongly indicate that the observations pertain to transitions between pendular states that result from the interaction of a strong optical field and the permanent polarizability anisotropy of the trimer. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Theoretical and experimental results pertaining to the excitation of intermolecular vibrations in the Raman and vibronic spectra of aromatic-containing, weakly bound complexes and clusters are reported. The theoretical analysis of intermolecular Raman activity is based on the assumption that the polarizability tensor of a weakly bound species is given by the sum of the polarizability tensors of its constituent monomers. The analysis shows that the van der Waals bending fundamentals in aromatic–rare gas complexes may be expected to be strongly Raman active. More generally, it predicts strong Raman activity for intermolecular vibrations that involve the libration or internal rotation of monomer moieties having appreciable permanent polarizability anisotropies. The vibronic activity of intermolecular vibrations in aromatic-rare gas complexes is analyzed under the assumption that every vibronic band gains its strength from an aromatic-localized transition. It is found that intermolecular vibrational excitations can accompany aromatic-localized vibronic excitations by the usual Franck–Condon mechanism or by a mechanism dependent on the librational amplitude of the aromatic moiety during the course of the pertinent intermolecular vibration. The latter mechanism can impart appreciable intensity to bands that are forbidden by rigid-molecule symmetry selection rules. The applicability of such rules is therefore called into question. Finally, experimental spectra of intermolecular transitions, obtained by mass-selective, ionization-detected stimulated Raman spectroscopies, are reported for benzene–X (X=Ar, –Ar2, N2, HCl, CO2, and –fluorene), fluorobenzene–Ar and –Kr, aniline–Ar, and fluorene–Ar and –Ar2. The results support the conclusions of the theoretical analyses and provide further evidence for the value of Raman methods in characterizing intermolecular vibrational level structures. [ABSTRACT FROM AUTHOR]

In application to benzene-Ar we test a procedure that makes use of conveniently calculated J=0 intermolecular eigenstates to compute molecular constants and transition intensities without requiring explicit diagonalization of the full rotational/intermolecular vibrational Hamiltonian of the species. The approach relies on the ability to calculate the orientation of an Eckart body-fixed frame for each point on a grid over which a J=0 state is represented. That ability allows one to compute vibrational matrix elements of operators referred to the Eckart axes while working with J=0 eigenstates obtained in an entirely different body-fixed frame. Generally excellent agreement is found between the Eckart results and those obtained by others via diagonalization of the full rotational/intermolecular vibrational Hamiltonian. Finally, a general prescription for the construction of an efficient rovibrational basis from J=0 solutions in a convenient body-fixed frame is presented. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Usingthe CCSD(T) model, we evaluated the intermolecular potentialenergy surfaces of the He–, Ne–, and Ar–phosgenecomplexes. We considered a representative number of intermoleculargeometries for which we calculated the corresponding interaction energieswith the augmented (He complex) and double augmented (Ne and Ar complexes)correlation-consistent polarized valence triple-ζ basis setsextended with a set of 3s3p2d1f1g midbond functions. These basis setswere selected after systematic basis set studies carried out at geometriesclose to those of the surface minima. The He–, Ne–,and Ar–phosgene surfaces were found to have absolute minimaof −72.1, −140.4, and −326.6 cm–1at distances between the rare-gas atom and the phosgene center ofmass of 3.184, 3.254, and 3.516 Å, respectively. The potentialswere further used in the evaluation of rovibrational states and therotational constants of the complexes, providing valuable resultsfor future experimental investigations. Comparing our results to thosepreviously available for other phosgene complexes, we suggest thatthe results for Cl2–phosgene should be revised. [ABSTRACT FROM AUTHOR]