Low-lying transitions

The ORD exhibits a bisignate nonresonant feature that cannot be explained with the intensity of low lying transitions. 

The most recent study, using UHF, MP2, BLYP and B3LYP methodologies, reached somewhat different conclusions. Density functional theory calculations showed one imaginary frequency for the rhombic structure (four equivalent bonds, 157.3 pm), suggesting that it is a (very low-lying) transition structure between two parallelograms (two pairs of equivalent bonds, 149.5 and 169.5 pm, respectively)... 

Several distinct energy loss peaks appear within the MgO band gap (between 1 and 5.5eV energy loss [218]) as a function of cluster size. These loss peaks cannot be assigned to low-lying transitions in the atom or in the ion [103,208,219,220]. EEL spectra of vapor deposited Ag, which forms islands and thin films via surface diffusion at sample temperatures between T = 100 and 500 K, have shown losses at 3.8 and 3.2 eV attributed to an Ag surface plasmon and to an Ag-MgO interface plasmon, respectively [218]. In contrast, the EEL spectra shown in Fig. 1.44 and recorded at T = 45K exhibit clearly a size dependence, which reflects the change in the electronic structure of the clusters. A similar behavior has been observed in optical absorption spectra of Ag (n < 21) clusters deposited in rare gas matrices [221], which has been interpreted as a manifestation of collective excitations (Mie plasmons) of the s electrons influenced by the ellipsoidal shape of the clusters. Some similarities but also some differences in the general trend with cluster size have been observed by comparing the optical absorption data shown in [221] with these EELS data [214]. In this context, it is important to note that EELS probes... 

Both the rotational tunneling transition and the transitions to the first excited librational state can readily be observed by INS techniques [19-22, 35]. Neutrons are extremely well suited as probes for molecular rotations when the motion involves mainly H atoms. The INS studies allow observation of low-lying transitions within the ground librational state of the (tunnel splitting), which corre-... 

DFT computations showed that the intramolecular addition of the aryllithium generated from 425 occurs on the central carbon atom of the allenic moiety to yield the intermediate 427 from which lithium ethoxide is eliminated to furnish the benzofuran product 426. Both cyclization processes were found to pass through low-lying transition states, as it would be expected for fast reactions at low temperatures [123]. Further explorations on the anti selectivity in the intramolecular carbolithi-ation by DFT computations revealed additional details regarding the mechanism of this carbocyclization and led the authors to conclude that such a transformation is controlled by the appropriate molecular editing [123]. The synthesis of functionalized heterocycles can be relatively easy to achieve by intramolecular carbometallation reactions. For example, Kunz and Knochel [124] recently reported the preparation of benzothiophene scaffolds 429 by copper-catalyzed carbomagnesiation ofalkynyl thioethers 428 (Scheme 10.148). 

The luminescence and excited state electron transfer reactions of (dppe)Pt S2C2(2-pyridine(ium))(H) and (dppe)Pt S2C2(4-pyridine(ium))(H) are dependent on the protonation state of the pyridine [30-35]. The switching on of the luminescence in these compounds results from a change in the ordering of the electronic transitions in the pyridine and pyridinium substituted complexes. Unlike the quinoxaline-substituted complexes, the neutral pyridine complexes have a lowest lying d-to-d transition, which leads to rapid nonradiative decay of the ILCT excited states. However, upon protonation the ILCT becomes the low-lying transition. The pyridinium complexes are room temperature lumiphores with emission from ILCT and ILCT excited states (see Table Ic). 

---