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Rotational coherence spectroscopy has been applied in a structural study of anthracene-(Ar), (n = 0-3), 9,10 dichloroanthracene-(Ar), (n = 0, l), and tetracene-Ar. Geometries consistent with the experimental results have been determined for each of the species. These geometries are compared with previous structural predictions from minimum energy calculations and vibronic frequency shift rules and are considered in the light of other known aromatic-(&), structures.

The intermolecular potential-energy surface pertaining to the interaction between benzene and N 2 is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene-N 2 van der Waals complex using the coupled cluster singles and doubles including connected triples ͓CCSD͑T͔͒ method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1 f 1g 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 2 isotopomers. Experimentally, intermolecular Raman spectra of jet-cooled h 6 -and d 6 -benzene-N 2 measured at 0.03 cm Ϫ1 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 6 axis. These Raman data, together with measured rotational constants and binding energies obtained by other groups on benzene-N 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.

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We report the results of rotational coherence spectroscopy on tolane, tolane–Ar, and tolane–N2. The results on tolane are consistent with a planar geometry for the species. They also provide information about the symmetries of excited vibronic states in the species. The results on the van der Waals complexes provide significant experimental constraints on where the small species bind to tolane. In addition, we report the observation of a rapid excited-state decay process in the complexes and discuss the possible nature of this process.