Nuclear rearrangement dynamics

Charge density-NMR chemical shift correlation in organic ions, 11, 125 Charge distribution and charge separation in radical rearrangement reactions, 38, 111 Chemically induced dynamic nuclear spin polarization and its applications, 10, 53 Chemiluminesance of organic compounds, 18, 187 Chiral clusters in the gas phase, 39, 147... 

Formation of specific complexes in the excited states ( exciplexes )f 35 52 85) Exciplexes are complexes not present in the ground state that form due to the extensive redistribution of electron density that occurs upon excitation. Among exciplexes, there may be some whose formation does not require substantial nuclear rearrangements and thus occurs rather rapidly even at 77 K. The formation of exciplexes is accompanied by a spectral shift to longer wavelengths. It is postulated that the fluorescence from tryptophan in proteins in a variety of cases is fluorescence from tryptophan exciplexes)35 85) In studies of the effects of environmental dynamics on the spectra, the exciplexes may be considered as individual fluorophores. 

In Ref. [9] we demonstrated how one approaches the DCL for the CC absorption cross section, Eq. (31). In a first step, the overall time evolution operator exp(iHcct/k) has to be replaced by the 5-operator 5i(t, 0) which includes the difference Hamiltonian of the excited CC state and of the ground-state. Then, the vibrational Hamiltonian matrix appearing in the exponent of 5i(t, 0) is replace by an ordinary matrix the time-dependence of which follows from classical nuclear dynamics in the CC ground-state. The time-dependence of the dipole moment d follows from intra chromophore nuclear rearrangement and changes of the overall spatial orientation. At last, this translation procedure replaces the CC state matrix elements of the 5-operator by complex time-dependent functions... 

The ion pair spin multiplicity may be a valuable tool to affect the BET rates and to probe the ion pair dynamics via magnetic field effects [36], Even weak magnetic fields are known to influence relative probabilities of singlet and triplet reactions [34], Chemically induced dynamic nuclear polarization (CIDNP) is a particularly informative technique [12]. Many bond scission reactions and rearrangements in cyclic radical ions have been successfully explored using this approach. Both structural data (spin densities) and approximate kinetic informations are indirectly available from such experiments [12]. 

A model of the photochromic effect based on the concept of the pseudo JTE was suggested in [ 196- 197]. This vibronic model allows us to examine the microscopic physical origin of the nuclear rearrangement and the underlying mechanism of the photochromic effect at the electronic level. At the same time the pseudo JTE approach can be considered as a background for the dynamical (quantum-mechanical solution) of the problem of light absorption and emission including the crucial question of interpretation of the anomalous lifetimes for the excited states and shape-functions of the optical bands. 

A search for an ionic Cope rearrangement has included (608). A concerted mechanism can only interchange (608) and (609), whereas (610) may intrude if ions (radicals) are involved. In fact, (610) is the product, and the absence of chemically induced dynamic nuclear polarization (CIDNP) effects together with trapping of the intermediate carbonium ion with borohydride as anethole support an ionic mechanism. ... 

In 1969, Jemison and Morris followed the Stevens rearrangement of A, iV-dimethyl-4-nitrobenzylamine acetamide by NMR and noted a chemically induced dynamic nuclear polarization effect on benzylic protons consistent with a benzyl radical. They postulated that this Stevens-type rearrangement of a benzyl group from an ammonium center to a negatively-charged nitrogen center occurred via a homolytic dissociation... 

Yang, L., Zhang, M., Liu, Y, Liu, Z., and Chow, Y.L., Triplex promoted intersystem crossing of ion-radical pairs in the photosensitized valence isomerization of quadricyclane chemically induced dynamic nuclear polarization (CIDNP) evidence,/. Chem. Soc., Chem. Commun., 1055-1056,1995. Kajitani, M., Fujita, X, Hisamatsu, N., Hatano, H., Akiyama, X, and Sugimori, A., Photochemical reactions of several adducts of metalladithiolenes and metalladithiazoles. Dissociation and rearrangement, Coord. Chem. Rev., 135, 175-180, 1994. 

To properly describe electronic rearrangement and its dependence on both nuclear positions and velocities, it is necessary to develop a time-dependent theory of the electronic dynamics in molecular systems. A very useful approximation in this regard is the time-dependent Hartree-Fock approximation (34). Its combination with the eikonal treatment has been called the Eik/TDHF approximation, and has been implemented for ion-atom collisions.(21, 35-37) Approximations can be systematically developed from time-dependent variational principles.(38-41) These can be stated for wavefunctions and lead to differential equations for time-dependent parameters present in trial wavefunctions. 

A formulation of electronic rearrangement in quantum molecular dynamics has been based on the Liouville-von Neumann equation for the density matrix. Introducing an eikonal representation, it naturally leads to a general treatment where Hamiltonian equations for nuclear motions are coupled to the electronic density matrix equations, in a formally exact theory. Expectation values of molecular operators can be obtained from integrations over initial conditions. 

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