Frank-Condon effect

For stereoelectronic reasons (overlap of reacting orbitals), the two reacting groups, H and X, must be either antiperiplanar or synperiplanar. During an electron transition there should be the least change in the position of the atoms involved (Frank-Condon effect). Strong bases with a large steric requirement will suppress the S 2 mode of reaction. 

Fig. 11. Ranges of kinetic energies and densities of species typically present in glow discharge plasmas. A=secondary electrons accelerated through the sheath, B=ions backscattered from cathode (most likely neutralized), C=ions accelerated towards cathode, D=electrons in bulk plasma, E=hot ions and neutrals formed in dissociation reactions (Frank-Condon effect), F=ions in bulk plasma, and G=neutral atoms and molecules. After [39].

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-... 

Radiationless transitions often show a pronounced deuteration effect. This effect should be discussed. Notice that coh — /2cod, and Sh — Sd/V2 and that the deuteration effect can be estimated by using the Frank-Condon factor for a displaced oscillator by using the energy law expression. In this case, it is found that... 

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. 

In asymmetric complexes of the type [(bpy)2RuCl(pi-pyz)Ru-(NH3)4L]4+, studies (94) revealed that there is a solvent donor-number (DN)-dependent contribution to the Frank-Condon barrier of approximately 0.006 eV/DN, which completely overwhelms the dielectric-continuum-theory-derived (l/Dop-l/Ds) solvent dependence typically observed in symmetrical dimers. In this case, variations in MMCT Eop with solvent give linear correlations when plotted against solvent dependent AEm, the difference in potential between the two ruthenium(III/II) couples, as shown in Fig. 10. The microscopic origin of this solvent effect was described by Curtis, Sullivan, and Meyer (122) in their study of solvatochromism in the charge transfer transitions of mononuclear Ru(II) and Ru(III) ammine complexes. The dependence... 

The interchain hopping transport can be described by the probability Ql(x) -where x is the effective conjugation or delocalization length-of finding a comparable mean free path on another chain weighted by the Frank-Condon factor FC. The conductivity a can then be described as a function of the concentration C of polarons, multiplied by the integral over the interchain hopping probability Pp(x) [96, 97]. 

Frank-Condon transition) define the potential energy surface. The meaning of the parameters is clear - energy stabilization due to the JT effect is given by the value of Ejy (or alternatively by E c = Eji), and direction and magnitude of the distortion by the Rjy. 

For all except one of the chemical ionization studies reported so far, the reactants initiated an acid-base, even-electron chemistry. For such reactants there are several reasons to anticipate that the spectra produced by chemical ionization will differ significantly from the spectra produced by electron impact, photon impact, or field ionization. The chemical ionization is effected by the transfer of massive entities such as protons, hydride ions, or alkyl carbonium ions. Consequently the chemical ionization processes are not governed by Frank-Condon considerations, and the ions produced by the transfer of even-electron entities are, for even-electron molecules, even-electron ions. The amounts of energy which are involved in chemical ionization processes tend to be low by mass spectrometric standards, although the exact amount involved depends upon the identity of the reactant used. 

The microenvironment viscosity may also affect the excited state relaxation process. In fluid solution at ambient temperatures, solvent relaxation occurs much faster than radiative decay, and the probe emits from the solvent-relaxed excited state. However, in viscous solutions radiative decay may compete effectively with solvent relaxation, resulting in a broad emission band containing contributions from both the Franck-Condon and relaxed states. Temperature is also important, since a solution will become more viscous as the temperature is decreased. At very low temperatures, the fluorophore becomes immobilised in a viscous glass, and emission arises from a state very close in energy to the Frank-Condon state. 

The term d, Rq describes the linear HT-interaction. It lemls to appearance of one-phonon transitions in an optical band. HT-interaction describes the effect of mixing of various electronic states due to phonon modulation. This mixing is fairly small. Therefore, HT-interaction, as a rule, is smaller than the linear Frank-Condon interaction. However, HT-interaction results in the temperature dependence of the integral intoisity of the whole optical band ... 

TDDFT calculations usually do not consider the effects of nuclei vibrations on the resulting spectrum. This can be accounted for via the Frank Condon approximation in which the overlap between the ground and excited vibrational eigenfunctions are calculated. This is the approach followed by Dryza et al. [108] to investigate spectra of naphtalene with a nitrogen substitution or by Zhang et al. [Ill] to describe the electronic excitation between vibrationally excited states of benzo[a]pyrene. 

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