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Internal rotational predissociative levels of OH–Ar (A 2Σ+) have been identified lying up to 350 cm-1 above the OH A 2Σ+ (v=0, 1)+Ar dissociation limit. The predissociative level energies, lifetimes, and OH A 2Σ+ rotational product distributions have been measured. Complexes prepared in many of these predissociative levels are long lived with lifetimes ≥50 ps. A novel variation of stimulated emission pumping has enabled quantitative OH A 2Σ+ rotational distributions to be obtained following OH–Ar predissociation. The OH product distributions are highly selective. The highest energetically available channel is always populated, yet in many cases, low rotational levels are conspicuously absent. The OH–Ar predissociative levels have been assigned nearly good quantum numbers based on a rotational contour analysis of the predissociative features and/or the OH A 2Σ+ rotational product distributions. A two-step mechanism involving Coriolis coupling and the potential anisotropy has been proposed to describe the predissociation process. A comparison between the experimentally measured and theoretically calculated observables provides a guide for further refinements of the OH A 2Σ++Ar potential energy surface. [ABSTRACT FROM AUTHOR]

A model for the rovibrational energy levels of a complex formed between a rare gas atom and a spherical top molecule is developed, specifically for a tetrahedral XY4 molecule in its ground and its triply degenerate vibrational states. Under the assumption that the tetrahedral molecule remains undistorted upon complexation, a large amount of the tetrahedral symmetry is retained in the complex. Using symmetry adapted terms to represent the anisotropy of the intermolecular potential, the perturbations to the energy levels of the tetrahedral molecule caused by the intermolecular potential have been considered. Correlation diagrams showing the pattern of these internal rotor states between the free rotor and rigid molecule limits have been constructed. [ABSTRACT FROM AUTHOR]

The infrared spectrum of Ar–SiH4, a rare gas–spherical top van der Waals complex, has been recorded in the vicinity of the silane ν3 triply degenerate stretching vibration ∼2189 cm-1. A complex, dense spectrum is observed, and this is due to the observation of 12 bands with origins corresponding to transitions between different internal rotor states of the silane molecule within the complex. From the analysis of the rotational structure within each band, the average argon–silane separation is determined to be 4.043 Å in the ground vibrational state and 4.046 Å in the excited vibrational state with v3=1. Using a model developed previously and a very simple form for the intermolecular potential, these 12 bands have been assigned and an effective anisotropic intermolecular potential for the internal rotation of the silane molecule within the complex has been determined. The vibrational anisotropy responsible for lifting the threefold degeneracy of the ν3 vibration is found to be fairly small, of the order of 1 cm-1, while the rotational anisotropy is much larger, of the order of 90 cm-1. [ABSTRACT FROM AUTHOR]

Metastable levels of OH–Ar which lie significantly above the OH (A 2Σ+)+Ar dissociation limit are identified. The rates of internal rotational predissociation and the resultant OH (A 2Σ+) product rotational distributions are determined. Comparison with theoretical calculations of the predissociative states provides a sensitive test of the short-range interaction potential. [ABSTRACT FROM AUTHOR]

We use slightly modified versions of earlier ab initio potential energy surfaces for Ar+NH(a 1Δ) and Ar+NH(c 1Π) to investigate the bend–stretch levels of ArNH complexes, both within an adiabatic bender model and in full variational calculations. The positions of these levels are used to reinterpret the fluorescence excitation spectra reported previously [R. W. Randall, C.-C. Chuang, and M. I. Lester, Chem. Phys. Lett. 200, 113 (1992)]. The first 15 observed bands can be unambiguously assigned, with near-quantitative accuracy. The weak anisotropy in the lower electronic state [ArNH(a 1Δ)] complicates the rotational structure, since each band involves overlapped transitions out of several, nearly degenerate bend–stretch levels of the complex. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]