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The benzene-Ar ground-state S(0) intermolecular potential energy surface is evaluated using the coupled cluster singles and doubles model including connected triple corrections and the augmented correlation consistent polarized valence triple-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The surface is characterized by absolute minima of -390.1 cm(-1) where the argon atom is located on the benzene C(6) axis at distances of +/-3.536 A, and has a general shape close to the available ground-state S(0) and the first singlet S(1) and triplet T(1) excited-state surfaces. Using the potential, the intermolecular level structure of the complex is evaluated. The new intermolecular potential energy surface gives very accurate results and improves those previously available.

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]

The intermolecular potential-energy surface pertaining to the interaction between benzene and N[sub 2] is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene-N[sub 2] van der Waals complex using the coupled cluster singles and doubles including connected triples [CCSD(T)] method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. After fitting the energies to an analytic function, the intermolecular Schrödinger equation is solved to yield energies, rotational constants, and Raman-scattering coefficients for the lowest intermolecular levels of several benzene-N[sub 2] isotopomers. Experimentally, intermolecular Raman spectra of jet-cooled h[sub 6]- and d[sub 6]-benzene-N[sub 2] measured at 0.03 cm[sup -1] resolution by mass-selective, ionization-detected stimulated Raman spectroscopies are reported. Seven intermolecular bands are assigned for each isotopomer, including transitions involving intermolecular bending and stretching vibrations and internal rotation about the benzene C[sub 6] axis. These Raman data, together with measured rotational constants and binding energies obtained by other groups on benzene-N[sub 2], agree well with the theoretical results. Such agreement points to the promise of the quantum chemical methodology employed herein in future investigations of larger van der Waals complexes. [ABSTRACT FROM AUTHOR]

Discusses the results of nonlinear Raman spectroscopy on the intermolecular transitions of the perprotonated and perdeuterated isotopomers of benzene-Ar. Bands observed for each species; Performance of band-contour measurements; Comparison of the results to simulated contours.

Mass-selective, ionization-detected stimulated Raman spectroscopies have been applied to a study of low-frequency structure in the ground states of benzene dimer isotopomers. The results reveal two Raman bands below 10 cm-1, as well as structure in the range of 47 to 53 cm-1. Tentative assignments for the bands are proposed. [ABSTRACT FROM AUTHOR]

The characteristics and origin of a new type of rotational coherence effect—asymmetry transients—are considered. Asymmetry transients are of two types, which we call C-type and A-type, respectively. C-type features are spaced by time intervals equal to 1/(4C). A-type features are spaced by time intervals equal to 1/(4A). Both types of transients can provide information on rotational constants that is not available from other types of rotational coherence effects. We show that the C-type transients arise from coherences between rotational eigenstates of the form Jτ and (J+2)τ-2 (in the Jτ notation) and that the A-type ones arise from coherences between eigenstates Jτ and (J+2)τ+2. The fact that such coherences produce asymmetry transients is shown to be a consequence of the limiting behavior of asymmetric top energy levels at high values of J. Experimental results in which asymmetry transients are present are reported for jet-cooled perylene, tryptamine (D conformer), 1-naphthol–water, and fluorene–benzene. [ABSTRACT FROM AUTHOR]

We apply a method for the construction of rotational-intermolecular vibrational states to the van der Waals molecule benzene-N[sub 2]. The method, as described in Felker et al. [J. Chem. Phys. 114, 1233 (2001)] is based on the transformation of approximate rovibrational eigenfunctions from functions of coordinates referred to an Eckart body-fixed axis system to functions of coordinates referred to a more convenient body-fixed frame. This transformation allows the computation of approximate rovibrational eigenenergies, as well as other molecular properties, from one or a small set of J=0 eigenfunctions. By comparing rovibrational energies and matrix elements computed by this Eckart method with those computed variationally with a large basis, we show that the former yields excellent results for benzene-N[sub 2]. The results are particularly significant because of the presence of essentially free internal rotation in the species, a large-amplitude motion that complicates the definition of an Eckart frame. © 2001 American Institute of Physics. [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]