Effective potentials predissociation

Effective potential curves and wave functions for the closed (segment A) and open (segment B) channels, and the off-diagonal coupling function and golden rule integrand (segment C) for the (J=0) predissociation H2(l,0)-Ar H2(0,0)+Ar. 

The problem lies in the assumption required to derive the selection rule that the u=l and u=0 surfaces are the same shape and are merely displaced vertically as we have illustrated in Fig. 2. For HF HF on the contrary, the intermolecular potential is highly anisotropic and rotational excitation of the fragments results in an effective potential which is shallow and may actually cross other surfaces. This has been demonstrated in calculations of Halberstadt et al.. The surfaces taken from their work are shown in Fig. 4. The curve crossing yields relaxation times orders of magnitude more efficient than those calculated by our selection rule. It is a challenge to the theorists to model the predissociation process, consistent with experiment, that allows both HF molecules to rotate on fragmentation. Clearly anisotropic effects will play an important role in understanding vibrational predissociation in other systems as well-for example, in the electronically excited state of OH Ar by Lester et al.. ... 

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 simulations demonstrated, that after the pump excitation of the iodine molecules into their B state three elementary dynamical processes determine the further reaction course (i) the predissociation of the iodine molecules caused by the coupling of the electronic B state to the repulsive ajo states, (ii) the electronic transitions from these states to the A, A, and X states due to the caging effect, and (iii) the vibrational relaxation in all electronic states involved in the reaction. Additionally, an energy shift of the potential curves due to the influence of the crystalline DDR cage could be observed. 

Rates for nonradiative spin-forbidden transitions depend on the electronic spin-orbit interaction matrix element as well as on the overlap between the vibrational wave functions of the molecule. Close to intersections between potential energy surfaces of different space or spin symmetries, the overlap requirement is mostly fulfilled, and the intersystem crossing is effective. Interaction with vibrationally unbound states may lead to predissociation. 

Zhao and Rice extended the above-sketched Gray-Rice theory to include the effects of intramolecular energy transfer, using analytical approximations for various quantities [15]. Because this extension is in the same spirit as in the case of unimolecular predissociation, the Zhao—Rice approximation presented here is still called the MRRKM theory. Zhao and Rice employed a model double-well potential similar to that used by Gray and Rice, but parameterized to have greater flexibility. Specifically, the three terms in the potential of Eq. (201) are taken to have the following form ... 

This kind of resonance structure in the predissociation of HNO has also been seen in experiment [266], however, at values of J which differ considerably from those obtained in the dynamics calculations. A quantitative description of these mixing effects requires very accurate PES s, because the level structure — in the case of HNO the level structure of two different electronic states — has to be precisely reproduced. The two calculated potentials for HNO do not meet this requirement for example the vertical energy separation is wrong by about 0.1 eV. 

Effect of Diatom Stretching Dependence. The features of the poten-tial energy surface most central to a discussion of its effect on the predissociation process are not the individual radial strength functions V j((R), but rather the vibrational matrix elements (integrated over the diatom bond length) of the full potential... 

SFCCCC Calculations of Ar-Ho Atom-Vibrating Rotor vdW Complex. A more complete description of the rotational predissociation dynamics in vdW molecule should In principle also include the effect of diatom (H2) bond stretching. Currently only one potential surface, the 803(6,8) potential of Carl and LeRoy( ), contains detailed Information about Its dependence on the length of the diatom bond. The 803(6,8) Ar-H2 potential ( ) Is expanded in the form... 

Thus, the observed trend in lifetimes — (C2H )2 C2H HCl <excited mode, the amount of linear and angular momentum which must be incorporated into fragment motion, and the overall number of product channels available. This inferred mechanism is subject to further tests. These include measurements of product velocity and rotational distributions. Real time measurements of either the population in the initially pumped level or the appearance of product fragments would be of great significance. 

Predissociation effects may be treated in either the diabatic (crossing potential curves) or adiabatic (noncrossing curves) representation. Criteria for choosing the more convenient representation are discussed in Section 3.3.4. When the adiabatic representation is appropriate, predissociative interactions between states of the same symmetry result from the nuclear kinetic energy operator. The matrix elements of this operator cannot be factored in the same way as Eq. (7.5.14) because the electronic element... 

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