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Transition linear-bent

The acetylene A <- X electronic transition is a bent <- linear transition that would be electronically forbidden ( - ) at the linear structure. The usual approximation is to ignore the possibility that the electronic part of the transition moment depends on nuclear configuration and to calculate the relative strengths of vibrational bands as the square of the vibrational overlap between the initial and final vibrational states (Franck-Condon factor). A slightly more accurate picture would be to express the electronic transition moment as a linear function of Q l (the fra/w-bending normal coordinate on the linear X1 state) in such a treatment, the transition moment would be zero at the linear structure and the vibrational overlap factors would be replaced by matrix elements of Qfl- Nevertheless, as long as one makes use of low vibrational levels of the A state, neglect of the nuclear coordinate dependence of the electronic excitation function is unlikely to affect the predicted dynamics or to complicate any proposed control scheme. [Pg.602]

Cossart-Magos C, Launay F, Parkin JE (1992) High resolution absorption spectrum of CO2 between 1750 and 2000 A. 1. Rotational analysis of nine perpendicular-type bands assigned to a new bent-linear electronic transition. Mol Chem Phys 75 835-856... [Pg.28]

Rh(TMP)- under these conditions, and in fact the selective activation of methane in benzene solution is a distinctive and unusual feature of this system, given that aryl C—H activation ought to be thermodynamically favored over alkyl C—H activation. The proposed linear transition state proposed in Fig. 8 is the key to this different reactivity. The corresponding trimolecular transition state for an arene would be expected to be bent, and this would be precluded by the bulky TMP... [Pg.303]

Smooth COSMO solvation model. We have recently extended our smooth COSMO solvation model with analytical gradients [71] to work with semiempirical QM and QM/MM methods within the CHARMM and MNDO programs [72, 73], The method is a considerably more stable implementation of the conventional COSMO method for geometry optimizations, transition state searches and potential energy surfaces [72], The method was applied to study dissociative phosphoryl transfer reactions [40], and native and thio-substituted transphosphorylation reactions [73] and compared with density-functional and hybrid QM/MM calculation results. The smooth COSMO method can be formulated as a linear-scaling Green s function approach [72] and was applied to ascertain the contribution of phosphate-phosphate repulsions in linear and bent-form DNA models based on the crystallographic structure of a full turn of DNA in a nucleosome core particle [74],... [Pg.384]

Pressure provokes transition of the linear (extended) conformation into the bent (V-like) one. (The V-like form is more compact and occupies a smaller volume.) It is obvious that the V-like form is favorable in respect of intramolecular electron transfer from the donor (the aniline part) to the acceptor (the pyrene part). In the utmost level of the phenomenon, the donor part transforms into the cation-radical moiety, whereas the acceptor part passes into the anion-radical moiety. Such transformation is impossible in the case of the extended conformation because of the large distance between the donor and acceptor moieties. The spectral changes observed reflect this conformational transition at elevated pressures. [Pg.282]

By writing about complexes containing triple bonds between phosphorus and transition metals, one has to take into account the triple-bond character of phosphinidene complexes which are in a nearly linear coordination mode (type C) in contrast to the usual bent coordination mode D possessing typical double-bond features. Due to the additional r-donation bonding ability of the PR moiety to the metal atom in type C and the observed bond lengths, this type of complexes has to be included into the classes of metal-phosphorus triple bond compounds. Thus, at the end of this review will appear a chapter highlighting the appropriate compounds of type C. [Pg.3]

For complex formation, simple and well established techniques are brought into action. Splitting of halogen bridged dimers or replacement of weakly bonded ligands such as THF would be successful the presence of only weakly coordinating anions could support the transition from a linear (ylene) arrangement into a bent structure to form L M CL2 compounds. [Pg.88]

Group theory has been useful in chemistry in several ways. First, it has provided simple, qualitahve explanations for the behavior of matter. For example, why can the states of electrons in any atom be classified, to a good approximation, by the four quantum numbers n, I, rrii and m Why, in their ground states, is BeH2 a linear molecule but H2O bent Why do certain transitions not appear in an absorption spectrum Lengthy computations can provide correct but uninformative answers to these questions group theory can provide perspicuous explanations of the factors that determine these answers. [Pg.1]


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Bent

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