Vibrational Predissociation Dynamics Research Articles

Weak van der waals complexes of the X … BC type: calculation of linewidths of metastable levels

We have applied a three-dimensional quantum model, very close to that of Beswick et al. (ref.1), to study the dynamics of vibrational predissociation (VP) of the He … I 2* van der Waals molecule near the dissociation limit of the I 2, subunit. The half-linewidth for vibrational predissociation Γ 2 as a function of the vibrational excitation of I 2 exhibits a maximum about v I = 57 in agreement with the experimental behaviour found by 2 Sharfin et al. (ref.2)

Weak van der Waals complexes of the x … bc type: Calculation of linewidths of metastable levels

We have applied a three-dimensional quantum model, very close to that of Beswick et al. (ref.1), to study the dynamics of vibrational predissociation (VP) of the He … I 2 ∗ van der Waals molecule near the dissociation limit of the I 2 subunit. The half-line-width for vibrational predissociation ▪as a function of the vibrational excitation of I 2 exhibits a maximum about v I = 57 in agreement with the experimental behaviour found by 2 Sharfin et al. (ref.2)

Vibrational predissociation spectra and dynamics of small molecular clusters of H2O and HF

Experimental results are presented for the vibrational predissociation spectra in the frequency range 3000–4000 cm–1 for the species (HF)n and (H2O)n, n= 2–6, using molecular-beam techniques and a tunable infrared laser. The observed spectra show a dramatic change between the dimer and larger clusters which is thought to be a result of the cyclic structure of the trimer and larger clusters. The spectra are compared with calculated harmonic force constants of available intermolecular potentials to understand how these small, gas-phase clusters relate to the liquid and solid phases of HF and H2O. Additionally, the angular distributions of the predissociation products show that little energy appears as translational motion of the fragment molecules. This conclusion is consistent with recent theoretical models of the predissociation process. An upper limit of ca. 2 µs is observed for the lifetime of the vibrationally excited clusters.

Vibrational predissociation lifetimes of the van der Waals molecule HeI2

In this paper we present a quantum mechanical study of the rates of vibrational predissociation of the T-shaped HeI2(B) van der Waals molecule. The van der Waals bond is characterized in terms of Morse type atom–atom interaction and by a Buckingham type atom–atom potential. The dynamics of vibrational predissociation is shown to be insensitive to the long-range part of the van der Waals potential and the Morse form is adequate for the description of this process. The close-coupling equations for nuclear motion are solved by standard numerical methods and the vibrational predissociation rates are related to the widths of the resulting resonances. The superlinear theoretical dependence of the vibrational predissociation rates on the excess vibrational energy of the molecular I2 bond is in good agreement with the experimental data. The relative contribution of intramolecular and of intermolecular terms to this superlinear dependence are elucidated, demonstrating the effects of the anharmonicity of the molecular bond on the intramolecular dynamics.

Vibrational predissociation of triatomic van der Waals molecules

In this paper we advance a quantum mechanical colinear model for vibrational predissociation on a single electronic potential surface of a linear triatomic van der Waals molecule X⋅⋅⋅BC, where BC is a conventional diatomic, while X represents a rare-gas atom. The zero-order states of the system are represented as products of an eigenfunction of the vibrating BC bond and a function describing the (bound or unbound) motion of X relative to the center of mass of BC bond which is frozen at its equilibrium configuration. The residual interaction representing the deviation between the interaction potential of X with the vibrating BC molecule, and the interaction of X with the frozen diatomic, induces discrete–continuum and continuum–continuum coupling. On the basis of the analysis of these coupling terms we assert that the zero-order basis provides a reasonable description of the initial and final states. We have also demonstrated that the zero-order resonance widths are small relative to their spacings and, furthermore, we have shown that continuum–continuum couplings prevail essentially only between adjacent continua. The dynamics of vibrational predissociation were reduced to the problem of the decay of a single resonance into a manifold of adjacently coupled continua. Closed analytical expressions for the rate of vibrational predissociation and for the vibrational distribution of the products were derived incorporating the effects of discrete–continuum and continuum–continuum coupling. We have explored the dependence of the rate of vibrational predissociation on the frequency of the BC molecule establishing a new energy gap law for this process. We have also investigated the dependence of the rate on the potential parameter of van der Waals bond and on the mass of the rare-gas atom. Finally, a study of the nature of the final vibrational distribution of the diatomic fragment resulting from the vibrational predissociation process was provided.