Predissociation tunneling

Pine A S, Lafferty W J and Howard B J 1984 Vibrational predissociation, tunneling, and rotational saturation in the HF and DF dimers J. Chem. Phys. 81 2939-50... 

B. Decay of Metastable State through Tunneling (Predissociation)... 

Needless to say, tunneling is one of the most famous quantum mechanical effects. Theory of multidimensional tunneling, however, has not yet been completed. As is well known, in chemical dynamics there are the following three kinds of problems (1) energy splitting due to tunneling in symmetric double-well potential, (2) predissociation of metastable state through... 

The theory developed for tunneling splitting can be easily extended to the decay of the metastable state through multidimensional tunneling, namely, tunneling predissociation of polyatomic molecules. In the case of predissociation, however, the instanton trajectory cannot be fixed at both ends, but one end should be free (see Fig. 17). The boundary conditions are... 

Usually tunneling through a potential barrier is considered on the basis of the stationary Schroedinger equation with the use of matching conditions. A different approach has been developed by Bardeen (34). Bardeen s method enables one to describe tunneling as a quantum transition and to use the Golden Rule in order to evaluate the probability of penetration through the barrier. A similar method has been used in Section III to describe vibrational predissociation. This section contains a short description of Bardeen s method (see refs. 39,82-84). 

Fig. 1.2. Schematic illustration of electronic (a) and vibrational (b) predissociation. In the first case, the molecule undergoes a radiationless transition (rt) from the binding to the repulsive state and subsequently decays. In the second case, the photon creates a quasi-bound state in the potential well which decays either by tunneling (tn) or by internal energy redistribution (IVR).

Fig. 12.5. Zeroth-order potentials Veff(R-,j,Sl,J) defined in (12.7) for fl = 0 and several total angular momentum quantum numbers J. The excited rotational states can decay either by tunneling (shape resonances) or by rotational predissociation ( Feshbach resonances) as indicated by the horizontal arrows. The excitation through the IR photon originates from the vibrational ground state n = 0 which is not shown in the figure.

The presentation will be working within the linear response theory [28] which has been early used in spectroscopy by Bratos et al. [29]. It will not consider (1) predissociation since theoretical works [30-35], showed that it is negligible (2) tunneling effect [36 -1] since it is dealing with weak or intermediate H-bonds where this mechanism cannot play a sensitive role and (3) rotational structure [42-44]. 

A large intermolecular isotope effect has been reported in the decomposition of metastable (CH)+ and (CD)+ ions [582]. The decomposition was seen as an electronic predissociation and tunnelling was discussed to explain the magnitude of the observed isotope effect. 

So far the effect of nonadditivity in water has been studied in the context of various structural properties, vibrationally averaged structures, O-H frequency shifts [89], zero-point energies, rotational constants, cluster predissociation dynamics and tunneling splittings [58],... 

Predissociation Dissociation occurring by tunnelling from a bound to an unbound rovihronic state. In an absorption spectrum of a molecular entity, the appearance of a diffuse band region within a series of sharp bands, is called predissociation, since irradiation with frequencies within the diffuse region leads to effective dissociation. The energy of the band is smaller than that of the dissociation continuum of the bound state. 

E.E.Nikitin, Vibrational relaxation and vibrational predissociation as dynamical tunneling processes, Uspekhi Khimii 62,3 (1993)... 

Y. Kami and E.E.Nikitin, Vibrational predissociation quasiclassical tunneling and classical diffusion. Mol. Phys. 89,1327 (1996)... 

E. Nikitin and J. Troe, Vibrational predissociation quasiclassical tunneling through classieal chaotic sea, this volume... 

Vibrational Predissociation quasiclassical tunneling through the elassical ehaotie... 

Vibrational predissociation quasiclassical tunneling through classical chaotic sea 381... 

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