Excitonic interactions in naphthalene clusters

Abstract

Well-resolved vibronic spectra, recorded by resonance two-photon ionization, are analyzed for cold naphthalene cluster species. Spectra for isotopically pure tetramers and both pure and mixed isotopic trimer clusters provide information on resonant (excitonlike) interactions. An analysis of the spectra suggests that the tetramer geometry resembles bulk crystalline naphthalene, whereas the trimer structure minimizes direct contact interactions. Cluster geometry is similar in ground and excited states of these clusters and there is no direct evidence for rapid dynamics in the excited states, nor is there evidence of multiple geometric conformations. Analysis of the isotopically mixed trimers suggests a preference for the HDH conformation, rather than HHD. An empirical weak interaction model provides a successful descripton of the observed spectra. Excitonic splittings are approximately proportional to dipole transition strengths for the vibronically induced spectra, whereas low-intensity allowed origin transitions exhibit splittings that greatly exceed dipolar contributions. Both results indicte that the long-range intermolecular potential exceeds simple estimates. This method of analysis may be applicable to studies of larger clusters, providing new information on size-dependent structure and dynamics.

Structure of the Naphthalene Dimer from Rare Gas Tagging

“…In this spectral region, well-resolved spectra of naphthalene trimer and tetramer were obtained as long ago as 1990, making the structural assignments of those clusters reasonably secure. 4 These structures were later confirmed by Raman 26,27 spectroscopy and rotational coherence spectroscopy (for the case of the trimer). 28 By contrast, for the dimer only very broad and mostly unresolvable spectra were seen in the past and no decisive structural information can be derived from these.…”

Cooling and collisions of large gas phase molecules

“…In addition, the N 2 dimer has a rich internal vibrational spectrum, 21 with a typical mode spacing for the complex of B20 cm À1 . This suggests that the N + N + He -N 2 + He reaction is likely to proceed via effective two body processes:…”

Excitonic couplings and electronic coherence in bridged naphthalene dimers

“…Excitonic interactions depend strongly on the distance and relative orientation of the transition moments of monomer units. The geometry can be obtained from high-resolution vibronic spectra and nonlinear Raman spectroscopy (10,22,29). Extensive study of benzene has been carried out as well.…”

“…Supersonic beam techniques have made it possible to study the excited-state dynamics and obtain detailed information about geometries and intermolecular interactions in these clusters (8)(9)(10). Naphthalene is one of the most thoroughly studied chromophores in crystals and in the gas phase both theoretically and experimentally (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21).…”