Franck Condon region

Figure 19. Outgoing waves on the first three electronic states of H2O following excitation of the (B Ai) (X Ai) transition. Green and red lobes have positive and negative amplitudes, respectively. The gray-fiUed contour on the B surface represents the Franck-Condon region of excitation from the ground state. Reprinted from [75] with permission from the American Association for the Advancement of Science. (See color insert.)...

The first study, by Ismail et al. [153], used the CASSCF method with a 6-31G basis set and an active space of 14 electrons in 10 orbitals to locate conical intersections and pathways connecting them to the Franck Condon region. Two such conical intersections were identified in that work, the ci2 and ci3, as defined above. In that work the barrier leading to ci2 was calculated to be 10 kcal/mol, too high to make this conical intersection relevant. But the barrier leading to ci3 was found to be much smaller, 3.6 kcal/mol, and it was concluded that ci3 is involved in the dominant decay path. Reaching this intersection requires first a conical intersection between the nn state, which is vertically the Si state, and the non state, which is vertically the S2 state. Merchan and Serrano-Andres followed up this study [140] using a method... 

A major technological innovation that opens up the possibility of novel experiments is the availability of reliable solid state (e.g., TiSapphire) lasers which provide ultra short pulses over much of the spectral range which is of chemical interest. [6] This brings about the practical possibility of exciting molecules in a time interval which is short compared to a vibrational period. The result is the creation of an electronically excited molecule where the nuclei are confined to the, typically quite localized, Franck-Condon region. Such a state is non-stationary and will evolve in time. This is unlike the more familiar continuous-wave (cw) excitation, which creates a stationary but delocalized state. The time evolution of a state prepared by ultra fast excitation can be experimentally demonstrated, [5,7,16] and Fig. 12.2 shows the prin-... 

Fig. 12.2 Left The ground (X, solid line), excited (6, dashed line) and dissociative [a1g(3II), dotted line] electronic state potentials of the iodine molecule. The arrow indicates the electronic excitation. The initial excited wave packet is located in the Franck-Condon region near to the inner classical turning point of the B state. The transition from the B to the a state is forbidden by symmetry in the isolated molecule but becomes allowed when the molecule is placed in a solvent.

Fig. 31. Schematic potential energy diagram for interaction between absorbate A and a surface M. G is the ground state of the molecular complex, M" + A is an ionic state, (M + A) is an antibonding state, M + A is a state where the adsorbate is excited and the substrate is in its ground state, M + A is a state where the substrate is excited and the adsorbate is in its ground state. Possible electronic transitions from the ground state G to the various excited states are indicated by the shaded Franck-Condon region. Electron bombardment can presumably excite any of these states. (From Ref. )...

Excitation of the coupled A2, Bi states results in the decay rate designated X3 which appears to be nearly independent of cluster size. A small increase in the value of x3 appears to occur for (S02)m clusters from the monomer (0.6 ps) to the dimer (0.9 ps), but remains constant at about 1 ps for larger cluster sizes. A likely interpretation of the observed decay process can be found in a detailed computational study [6] which reports that following the initial vertical excitation of the 1 B state, the excited state wave packet travels from the Bi state into the double wells that result from the crossing of the 1A2 and Bi states. The transition of the excited state population into the double wells of the A2 and B states is believed to lead to the decay observed in the pump-probe experiment because the potential energy well minima of both of these states are outside of Franck-Condon region for the absorption of the probe laser pulse. Therefore, ion signal is not observed once the transition has occurred. The primary discrepancy between the computational results of Ref. [6] and the... 

The vibrational population of CH is independent of photon energy for a given electronic state above the Franck-Condon region. 

FIGURE 13. The dashed curve is part of a repulsive potential curve for IC1 constructed from experimental data (201). The solid line is taken from Child and Bernstein (216). Re denotes the ground state equilibrium distance and the horizontal line is the Franck-Condon region probed in the experiment. The figure was reproduced from reference (201) with permission of Elsevier Science Publishers. 

---