Selection rules modification

Cordonnier M, Uy D, Dickson R M, Kew K E, Zhang Y and Oka T 2000 Selection rules for nuclear spin modifications in ion-neutral reactions involving Hg" J. Chem. Phys. 113 3181-93... 

The above results indicate that the selection rules are relaxed when the geometry modifications taking place upon photoexcitation are considered. Although the transition dipole moment between the ground state and the lowest excited state remains small, the luminescence is no longer entirely quenched by the interchain interac-... 

It is natural to wonder whether changes need to be made to the selection rules worked out by Hellwege (1948). It would be strange if the powerful group-theoretical arguments he developed required modification just because some of the atoms in the crystal were not perfectly isotropic. The resolution of the paradox lies in the actual transition that was chosen to be studied. We concealed the fact that the D4 crystal field must mix a small amount of, say, D4,Mj = +3> into... 

In these oxides, the 6s and 5d and, to a lesser extent, the 4f electrons of the rare earth atom are mainly responsible for electrical transport and structural properties, whereas the localized 4f electrons govern the magnetic properties. X-ray absorption spectroscopy (XAS) offers the important advantage of simultaneously probing the 4f and the ds conduction states in these oxides. In XAS, the dipole selection rules are strictly obeyed and this facilitates the identification of the spectral features. Generally, the 3d—>4f (Mjv-v) or 4d—>4f (Niv-v) absorption transitions are studied. In these absorption processes the excited 4f electron participates directly in the transition. The resulting multiplet structure is observed to provide a finger-print of the 4f population of the rare earth atom. The modification in the valence band electron distribution introduced by the delocalization of a 4f electron is probed by the transition of a 2p (Ln-m) electron in the vacant sd conduction states. In this case the 4f electron does not participate direct in the transition. 

Because most of the molecules of interest in biophysics have very low symmetry, their vibrational modes cannot be described accurately as being either symmetric or antisymmetric, and the peaks in a Raman or resonance Raman spectrum cannot be assigned on the basis of simple selection rules. However, normal-mode analysis often can be used to identify the vibrational modes that are coupled most strongly to excitation of a chromophore. Isotopic labeling, chemical modifications of the chromophore, or site-directed mutagenesis can be used to shift a particular vibration to higher or lower frequency. 

The directional properties of the local field electromagnetic enhancement have been used to deduce the orientation of small molecules adsorbed on Ag colloids and electrodes. Moskovits and Suh and Creighton "" used these properties to deduce surface selection rules, which essentially are the modifications of band intensities due to the normal and tangential enhancement components of the local field of a molecule near a metal surface. Here the... 

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