Franck-Condon structure

The two species of 202 amu are taken to be the initially formed Franck-Condon structure and the parent species giving coherent resonance motion loss of a bromine atom gives BrCH2CH2CH2, which is detected after ionization by the probe pulse as C3H5, at 41 amu. The decay of BrCH2CH2CH2 leads to cyclopropane, a product not ionized by the probe pulse, and hence not seen through mass spectrometry. 

In Figure 31, we compare the associated spectrum of the fast component in 9-methyl adenine with calculated [194] Franck-Condon structures for the 7i7t —> Dq(n 1) +e (solid line) and 7171 —> Diin 1) + e (dash-dotted line) ionizing transitions. The two separated peaks agree well with the FC calculations, strongly suggesting that the short-lived state in 9-methyl adenine is the 7i7t state. By contrast, adenine contains an additional contribution that... 

The purpose of this paper was to illustrate the use of a completely classical model to study the laser enhancement of chemical reactions via a collision induced absorption. It is found that the model is easy to apply to a wide range of collinear and three-dimensional examples. It is interesting to note that the quantum mechanical calculation is in qualitative agreement with the classical calculation in the collinear A + BC examples and that a very simple calculation (as in Fig. 3) can predict the Franck-Condon structure in the quantum mechanical reaction. A further study of three-dimensional systems is necessary to see if the low-energy structure in the reaction probability is always weak or whether this is an artifact of the particular model. Other preliminary calculations have illustrated the laser inhibition of chemical reactions with very small field strengths as well as isotopic effects in these systems. Further work is necessary to explore these interesting possibilities. 

Figure Al.6.11. Idealized UV absorption spectrum of CO2. Note the regular progression of intemiediate resolution vibrational progression. In the frequency regime this structure is interpreted as a Franck-Condon...

A qualitatively different approach to probing multiple pathways is to interrogate the reaction intermediates directly, while they are following different pathways on the PES, using femtosecond time-resolved pump-probe spectroscopy [19]. In this case, the pump laser initiates the reaction, while the probe laser measures absorption, excites fluorescence, induces ionization, or creates some other observable that selectively probes each reaction pathway. For example, the ion states produced upon photoionization of a neutral species depend on the Franck-Condon overlap between the nuclear configuration of the neutral and the various ion states available. Photoelectron spectroscopy is a sensitive probe of the structural differences between neutrals and cations. If the structure and energetics of the ion states are well determined and sufficiently diverse in... 

The Franck-Condon question is also an issue in diradical studies. It is particularly relevant in nonrigid systems, such as trimethylenemethane (TMM) and tetramethyleneethylene (TME), °° in which neutral and/or anion states can be planar or nonplanar. Thus, transitions can occur from planar anions to nonplanar neutral states, or from nonplanar anions to planar neutrals. In these cases, the energy differences between the planar and nonplanar states have generally been estimated by using quality electronic structure calculations. 

Assignment of such spectra and fitting of model potential parameters to the observed band frequencies yields the magnitudes of V3 and V6 in the two electronic states involved, either S, and S0, or D0 and S,. Franck-Condon modeling of relative band intensities then yields the relative phase of the potentials in the two electronic states. We typically fix the absolute phase of the potentials from ab initio electronic structure calculations on both the S0 and D0 states. This provides an overall consistency check as well. 

From a molecular structure point of view, for diCN-HBO, the lone pair electrons of the benzo-nitrogen atom are intrinsically involved in the Ji-electron resonance to establish the aromaticity, such that its electron donating strength, compared with those of alkyl and aryl amines, is negligibly weak. Thus, upon Franck-Condon... 

Radiative transitions may be considered as vertical transitions and may therefore be explained in terms of the Franck-Condon principle. The intensity of any vibrational fine structure associated with such transitions will, therefore, be related to the overlap between the square of the wavefunctions of the vibronic levels of the excited state and ground state. This overlap is maximised for the most probable electronic transition (the most intense band in the fluorescence spectrum). Figure... 

Vibrational fine structure is absent from the excimer emission because the Franck-Condon transition is to the unstable dissociative state where the molecule dissociates before it is able to undergo a vibrational transition. In the case of the monomer emission, all electronic transitions are from the v = 0 vibrational level of M to the quantised vibrational levels of M, resulting in the appearance of vibrational fine structure. 

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