Photodissociation ground electronic state

In addition to the previously mentioned disadvantages, all of these methods have another drawback in the large molecule photofragment velocity measurements. For example, in the studies of UV photon photodissociation of polyatomic molecules, like alkene and aromatic molecules, molecules excited by the UV photons quickly become highly vibrationally excited in the ground electronic state through fast internal conversion, and dissociation occurs in the ground electronic state. 

Fig. 6.4. Schematic illustration of the multi-dimensional reflection principle in the adiabatic limit. The left-hand side shows the vibrationally adiabatic potential curves en(R). The independent part of the bound-state wavefunction in the ground electronic state is denoted by

In order to simplify the general picture we assume that the photodissociation separates into two consecutive steps as illustrated in Figure 7.5. The light pulse promotes the molecule from the initial nuclear state J o) in the ground electronic state to the vibrational-rotational states I J ii) with energies Ei in the (binding) excited electronic state. In the second step, the i/) couple to the manifold of continuum states and eventually they dissociate. Only the binding state is assumed to be dipole-allowed h-i iQ 7 0] whereas the dissociative state is dark p = 0]. 

The remainder of this paper is organized as follows In Sect. 5.2, we present the basic theory of the present control scheme. The validity of the theoretical method and the choice of optimal pulse parameters are discussed in Sect. 5.3. In Sect. 5.4 we provide several numerical examples i) complete electronic excitation of the wavepacket from a nonequilibrium displaced position, taking LiH and NaK as examples ii) pump-dump and creation of localized target wavepackets on the ground electronic state potential, using NaK as an example, and iii) bond-selective photodissociation in the two-dimensional model of H2O. A localized wavepacket is made to jump to the excited-state potential in a desirable force-selective region so that it can be dissociated into the desirable channel. Future perspectives from the author s point of view are summarized in Sect. 5.5. 

We use a basis set ij, A I, 5, G, N, F, M) where // is taken to represent different vibrational levels of the ground electronic state Jefferts measurements involved the v = 4 to 8 levels, these being the ones with the optimum populations and photodissociation cross-sections. The matrix elements of each term in (11.79) are now readily calculated. The Fermi contact interaction is found to be diagonal in the chosen basis ... 

In a photodissociation reaction it is usual for the initial state of the molecule to be the ground vibrational state of the ground electronic state. The incident radiation is resonant with an excitation to an electronic state that is dissociative (repulsive potential energy surface) or predissociative (the optically allowed transition is to a bound-state potential energy surface that intersects a repulsive surface). In the Franck-Condon picture, the electrons respond instantaneously to the incident light, while the relatively massive nuclei respond only slowly. Hence, on absorption of a photon the nuclear wave-function retains its shape but is projected up to the dissociative electronic state. In the traditional approach to the calculation of the photodissociation... 

If the excited 5 state is dissociative, the reaction generally takes place on the upper potential energy surface and is extremely fast. This class of reactions is often referred to as photodissociation, a topic discussed in a recent book (Schinke, 1992). On the other hand, if the excited state decays first by internal conversion to the ground electronic state, the reaction rate is much slower and more readily measured. 

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