Franck-Condon effects

Francium, binary carbide not reported, 11 210 Franck-Condon effect, 16 69 energy, 21 180, 188, 189 envelopes, 16 80, 89, 90 hot bands, 16 90 factors, 32 47 principle, 21 179, 181 vibronic replica, 35 370 frd redon, 38 412, 414 Freeze quench EPR spectroscopy (FQ-EPR), CODH/ACS, 47 318 Fremy s salt, 33 106 Friedel-Crafts reaction, 17 194 cyclophosphazene, 21 65, 66 Frontier molecular orbitals, heteronuclear gold cluster compounds, 39 378-381 Frozen solutions, MOssbauer spectra in studies of, 15 101-103... 

Based on the expression for, a large increase in the useful NLO coefficient for a fixed wavelength is predicted in the case where the absorbance of the NLO dye lies between the fundamental and second harmonic. Residual absorption at the second harmonic is the limiting factor in the practical application of this technique, and has been addressed through the synthesis of new dyes. Improvement of lOx in reducing this absorbance has been achieved, and another factor of 5-lOx is estimated to be required before practical devices can be fabricated. Franck-Condon effects (vibronic structure) appear to be responsible for this residual absorption because small, rigid chromophores are often correlated with the lowest amounts of absorption. Chromophores based loosely on... 

Keywords. Neutralization-reionization mass spectrometry, Ion chemistry, Collisional electron transfer, Franck-Condon effects, Reactive intermediates... 

Less is known about Franck-Condon effects on collisional electron detachment from anions. For example, the C-N bond in CH2N02 (1.401 A) is 4.5% longer than the same bond in the CH2N02 anion (1.340 A), and vertical neutralization results in 25-30 kj mol-1 vibrational excitation in the radical, as calculated at several levels of theory [18]. Alkoxy radicals and anions also show different C-0 bond lengths, e.g., 1.317 A and 1.371 A in the 1-pentoxy anion and radical, respectively [1], although the Franck-Condon energies associated with... 

The +NR+ spectrum of 8 showed a small survivor ion, but differed substantially from the spectra of other C2H5NO isomers, e.g., 6, 7, AT-methylamino(hy-droxy)carbene (9), and N-methylformamide (10). The low intensity of survivor ions in the NR mass spectra of enol imines is due to Franck-Condon effects in collisional reionization that result in vibrational excitation of the resulting cation radical followed by dissociation. Franck-Condon effects were studied for collisional ionization of acetimidic acid, CH3C(OH)=NH, which was one of the neutral dissociation products of 1 -hydroxy- 1-methylamino-l-ethyl radical, a hydrogen atom adduct to AT-methylacetamide [37]. The cation-radical dissociates extensively upon reionization, and the dissociation is driven by a 74 kj mol-1 Franck-Condon energy acquired by vertical ionization. 

The interpretation of Hop et al. [51] is consistent with ab initio calculations that predict a very shallow potential energy minimum for neutral ylid 33 that was bound by only 17 kj mol1 against dissociation to CH2 and HCl and, moreover, vertical electron transfer to 33+ was predicted to result in 84 kj mol 1 excess vibrational energy in the neutral ylid due to Franck-Condon effects [140]. 

Here /is the ionization potential of the quenching molecule and = [c/(Q) + (/(I )] /2 is the distance of closest approach of the collision pair, where the d values are taken as Lennard-Jones collision diameters deduced from viscosity measurements. Thus a plot of In (cr ) versus In aQfj j HI ) would be predicted to be linear. This model also predicts some variability for different v vibrational levels due to Franck-Condon effects, but this can be ignored in the present experiment where mainly the v = 32 level is excited by the 532-nm source. 

In a situation, when the purely electronic transition between an excited state and the ground state is allowed or not totally forbidden, a different vibrational activity, the Franck-Condon activity, can become dominant. This can lead, for example, to the occurrence of progressions. Although, the Franck-Condon effect is well known, it is appropriate to summarize briefly the background and to introduce the useful Huang-Rhys parameter. This summary is largely based on the descriptions found in the Refs. [96-100,154], in particular it is referred to Ref. [99, p. 200]. 

There are a number of ways in which the medium might be expected to influence Tji magnitudes (over and above the modest many-electron Franck-Condon effect noted above). By medium we refer to the environment of the DBA complex (Figure 1). Typically, it will be a polar solvent. Solvent molecules may, of course, constitute part of the bridge (e.g., in the case of solvent-separated ion pairs [118]), which does not necessarily consist of a complete sequence of covalent linkages between D and A [34, 60, 89, 110, 111],... 

Shape-Resonance-Induced Non-Franck-Condon Effects... 

One recent example has been the prediction and experimental confirmation of the role of shape resonances in producing non-Franck-Condon effects in vibrational branching ratios and photoelectron angular distribution. 

An important characteristic of shape resonances is that they cause non-Franck-Condon effects in vibrationally resolved photoionization spectra. These effects are a consequence of the strong R-variation of the transition moment caused by the R-dependence of the form of the continuum molecular orbital. 

Fig. 5. The corresponding overlap integrals are readily calculated from standard formulas. All these results are based on the assumption that the Raman scattering is due solely to Franck-Condon effects.

Fig. 7. Same plot as Fig. 6 except for an additional vibrational frequency change (

Fig. 9. Similar plot as Fig. 6 with the incident frequency scale extended so as to cover the absorption bands of both electronic states involved in the coupling. The large difference in overtone intensity between the two electronic band regions is due to a Franck-Condon effect, namely, co = 2co = f. The coupling is stronger and the states are closer ( q = 10)...

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