Frank-Condon region

Femtosecond photochemistry (267 nm) of gas-phase M(C0)6, M = Cr, Mo, W, Fe(CO)5, and Ni(CO)4, has established multiple processes in the first 1000 fs after excitation. For example, Fe(CO)5 undergoes five consecutive processes. The first four of which occur within 3300 fs and represent a continuous pathway from the Frank-Condon region down to the lowest singlet state of Fe(CO)4. The fifth stage corresponds to loss of a second carbonyl group. A review of this work appeared in 2001. In the case of Fe(CO)5, CASSCF/MR-CCI calculations have been carried out on the excited states. ... 

Figure 5 shows a plot of the magnitude of the overlap for / = 0, K0/ (f)> sl. versus time. The magnitude of the overlap decreases as the wavepacket spreads out. There is no recurrence. The steeper the inverted potential (i.e., the higher coj), the faster the wavepacket spreads out and the faster the overlap decreases. Because the inverted harmonic potential surface can model only a small area around the Frank-Condon region, this model can only be applied to short time dynamics. 

The absorption and fluorescence spectra of a neat film made of RdB-den-drimer are shown in Fig. 2. The absorption spectrum in visible-wavelength region was similar to that obtained from a solution of RdB with a concentration less than 0.1 mmol/1. Interpretation of the fluorescence in terms of the Frank-Condon mechanism indicated that the core RdB chromophore behaved with a site-isolation effect and had little interaction with the neighboring chro-... 

First, we present the dynamics of the initial wavepacket a. Initially the system stands at the equilibrium position of the electronic ground X. The temporal evolution of the wavepacket Pe generated in the electronic excited state is shown in the left-hand column of Fig. 5.9. Apparently, tp originates in the Frank-Condon (FC) region, which is located at the steep inner wall of the electronically excited A state. The repulsive force of the potential l 0 the drives e(t) downhill toward the saddle point and then up the potential ridge, where Pe(t) bifurcates into two asymptotic valleys, with Ye = 0.495 in channel f. The excitation achieved using this simple quadratically chirped pulse is not naturally bond-selective because of the symmetry of the system. The role played by our quadratically chirped pulse is similar to that of the ordinary photodissociation process, except that it can cause near-complete excitation (see Table 5.1 for the efficiency). This is not very exciting, however, because we would like to break the bond selectively. 

The minimal active space needed to describe the electronic structure of the NDI moiety includes the five occupied and five unoccupied 7t-orbitals of the naphthalene core and four lone pair orbitals of the carbonyl groups. The 57t[4n]57t active space contains 14 electrons and electronic transitions arise from seven states. Only two of the seven states, 1 1 B2u and 1 B3U, show transitions in the region of interest between 320 and 420 nm. Other transitions have no effect on the bands in this region and hence were not considered. The main features in the experimental absorbance spectrum were reproduced using the most intense Frank-Condon transitions (Fig. 15). The calculated spectrum (dashed lines) showed a red shift of 9 nm relative to the experiment, which may be due to the representation of each transition by only two charges, and also due to the neglect of other transitions. 

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