In this work a fully symmetrized quantum mechanical description of vibrational motion in terms of complex vibrational coordinates and complex basis wavefunctions is outlined, designed for studying vibrational level mixing and intramolecular vibrational energy redistribution (IVR) around CH stretch overtone states in benzene. Symmetrized local mode (LM) formalism has been applied to the CH stretch system, while the remaining benzene vibrations (including out-of-plane modes) were treated as normal modes (NM). Using the outlined approach a model calculation of the absorption spectrum of the first overtone state CH (n=2) at ∼6000 cm−1 has been carried out.

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In this article, we present a continuation of our work on the refinement of the harmonic force constants Fi,k in benzene (in symmetrized Whiffen's coordinates) and on a growing number of higher order (anharmonic) force constants, Fi,j,k and Fi,j,k,l, that are of importance for the benzene isotopomer invariant potential energy surface. The refined set of harmonic and anharmonic force constants improves the agreement between the experimental levels and those calculated theoretically. The emphasis of the present work is on the analysis of the two notable Fermi resonances in benzene (nu8 +nnu1 <=> (n +1)nu1 + nu6, where n = 0, 1, ... m, and nu20 <=> nu8 + nu19 <=> nu1 + nu6 + nu19). For this purpose, we have further extended our fully dimensional, fully symmetrized, and nonperturbative vibrational procedure to the vibrational structure of the benzene isotopic species with D6h symmetry.

The cross section for isolated-core excitation ͑ICE͒ of barium 6p j nЈkЈ autoionizing states from 6snk Stark levels has been measured as a function of applied electric-field strength. For the most part, states that are well mixed by the applied field have nearly Lorentzian line shapes indicating predominant ICE of a single autoionizing resonance with nЈϭn and kЈϭk. Small non-Lorentzian shake-up features in the wings of the lines are examined in detail using high laser power to depletion broaden the main resonance and amplify the wings of the line shapes. While analogous shake-up features in zero-field ICE spectra are easily described theoretically, attempts to reproduce the spectra observed in a field generally fail to provide good agreement. Finally, significant differences in excitation of Ba ϩ 6p 1/2 rather than Ba ϩ 6p 3/2 cores are observed.