No-phonon transition

Nonsteroidal antiinflammatory drugs, interaction with lithium, 36 66 No-phonon transition, 35 324 Norbomadiene complexes with cobalt, 12 286 with copper, 12 328, 330, 331 with gold, 12 348, 349 with group VIB metals, 12 231 with group VnB metals, 12 241 with iron, 12 265 with palladium, 12 314 with platinum, 12 319 with rhodium, 12 300-302 with ruthenium, 12 278, 279 with silver, 12 340-342, 344, 346 Norbomylsiloxane, 42 226, 228 Notch receptor proteins, 46 473, 475 h (N)" oxime complexes, osmium, 37 260 h (N,0) oxime complexes, osmium, 37 260 (NPr ljiFeCfrdto),], magnetization versus temperature, 43 230... 

The latter statement can be illustrated as follows. AVhen AR = 0, the vibrational overlap will be maximal for the levels v = 0 and v = 0, since the vibrational wave functions involved have their maxima at the same value of R, viz. R . The absorption spectrum consists of one line, corresponding to the transition from v = 0 to v = 0. This transition is called the zero-vibrational or no-phonon transition, since no vibrations are involved. If, however, AR 0, the v = 0 level will have the... 

Fig. 19. Composite two-photon excitation spectrum of the 4f ->5d transition in 0.003% in CaF, at 6K. The transition is studied by monitoring the 5d— 4f, no phonon transition occurring at 313.1 nm. As noted in text this transition is normally two-photon forbidden because of parity selection rules, however, odd crystal-fields components admix parity to make the transitions partially allowed. The pure electronic transition of the state is labeled as 0 other excitations, 1 to 12, are identified as phonon or normal mode excitations of the lattice which couple to the pure transition. Selection rules for assisted transitions follow selection rules which differ from the one-photon case. After Gayen and Hamilton (1982).

The widths of the phonon replicas I (1) and /2 (1) are only 2-4 times larger than the no-phonon lines, and this implies a relatively small coupling with the electronic transitions, which has been discussed by Kleverman et al. [100] in terms of a pseudolocalized phonon in the vicinity of the acceptor atom. The positions of the no-phonon acceptor lines of Au and Pt and of the phonon replicas of Pt in silicon are given in Table 7.18. 

Each pair (A and B) is considered as a no-phonon (NP) transition and its TO phonon replica. The pairs are supposed to originate from two subsets of dots. 

The very first laser, the ruby laser, belongs to the family of the transition metal ion lasers. However, its wavelength is fixed.Its lower lasing state is the ground state, the orbital momentum of which is quenched by the crystal field. There is no direct coupling of the lattice vibrations to this ground state, i.e. no phonon sideband can occur. 

The actual volume collapse during the y—a transition indicates that the electron-phonon interaction is an important factor. Hence it is expected that some anomaly will be seen in the phonon spectra, which is associated with a possible softening in the transition arising from the electronic contribution, as is discussed for La by Pickett et al. (1980). To our knowledge, no phonon spectra of a-Ce are available to date due to the difficulties of sample preparation. Once available, the comparison of phonon spectra in the various phases of Ce metal will yield crucial insights into the nature of the phase transition. We note that phonon data for y-Ce shows evidence for a phonon softening which may be related to the y - a transformation (Stassis et al. 1979, 1982). 

The lattice strains associated with vibrations in the solid modulate the crystal field. This influences the 4f spins via the spin-orbit interaction and thereby induces electron-phonon transitions between the Ln crystal-field levels. Such transitions represent an exchange of energy between the vibrational and electronic systems of the solid. A coupling of the lattice vibrations to the spins of a Ln " " ion of this type is referred to as van Vleck mechanism (Poole, 2004). The probability Ppg for a lattice-induced transition between two crystal-field levels p q is related to that for the reverse transition by Ppg=Pgpexp[(Ep Eg)lkT], whoro , is the energy of the crystal-field level i (GiU, 1975). Here, it is assumed that there is no phonon bottleneck (Auzel and Pelle, 1997), that is, that phonons with energy Ep — Eg can be created or annihilated as needed. In thermal equilibrium, the respective transition rates are equal over the ensemble of Ln ions, and the relative population of crystal-field level i at temperature T is given by... 

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