Electric dipole-allowed

The 4f — 4f65d1 transitions are electric dipole allowed, the intensity matrix elements being roughly the same in the D w and Ci geometries. 

The well-known tetrahedral [Co(NCS)4]2 ion has continued to attract attention from analytical chemists, physical chemists, and spectroscopists. The inelastic electron tunneling (IET) spectrum of (Me4N)2[Co(NCS)4] was compared with IR and Raman spectra of the same complex.359 The vibrational bands due to the Me4N+ were prominent in all three spectra, but Coligand stretches were absent from the IET spectra. The lowest 4 42 4T2 electronic transition was strong in the IET spectrum but absent from the IR spectrum. The electric dipole allowed 4A2 4TX electronic transition was observed in both the IET and IR spectra and no fine structure was observed. Complex formation equilibria between Co11 and SCN- were studied calorimetri-... 

At resonance with an electric dipole allowed transition, the Stokes resonance Raman scattering, I(tt/2), associated with a single totally symmetric mode and its overtones is proportional to... 

Some results are given in Figure 1 for [MnC ]", and related ones have been obtained for [ReS ]", [MoS ]2" and [WS ]2" (J -7), for each of which the lowest electric-dipole-allowed transition (1t2 Uj) is clearly vibronically structured (a situation which is brought about by the fact that ouj > r). The best fit 6 value derived for each ion (0.05-0.09 %) indicates that, in the T2 state, the change undergone is rather larger than that typical of a one-electron reduction of the ion e.g. 0.03 A for [MnO (8). 

The average energy flux in the evanescent wave is given by the real part of the Poynting vector S = (c/47t)ExH. However, the probability of absorption of energy per unit time from the evanescent wave by an electric dipole-allowed transition of moment pa in a fluorophore is proportional to lnfl - El2. Note that Re S and pa E 2 are not proportional to each other they have a different dependence on 0. 

We see that the electric dipole allowed transitions are, in general, much more intense than the magnetic dipole allowed transitions. In fact, the magnetic dipole contribution to an optical transition of a center dominated by an electric dipole character is usually completely masked by the much more intense J electric dipole transitions. 

After X-ray irradiation of thermally annealed NaCl crystals, a small percentage of divalent europium ions are converted into trivalent europium ions (Aguilar et al, 1982). This is shown by the appearance of weak and narrow absorption lines at around 460 nm and 520 nm, related to the Fq D2 and Fq Di transitions of Eu + ions, respectively. For our purposes, this example allows us to compare the different band features between (RE) + and (RE) + ions Eu + ions show broad and intense optical bands (electric dipole allowed transitions), while Eu + ions present narrow and weak optical lines (forced electric dipole transitions). 

These spectral differences can be understood through ligand field theory.(6) For two coordinate Cu(I) with an approximately linear geometry, the electric dipole allowed Is —> Ap transition is predicted to split Into Is —> Ap and Is —> Ap components. 

Thus the problem of deciding whether a certain transition is electric dipole allowed, and what the polarization is. reduces to that of deciding whicW. if... 

Our task here is to determine whether any of the three Cartesian components is nonzero. Since, in DAh the z vector transforms according to the AZu representation and a and y jointly according to the representation, we need to know whether either of the direct products, Blg x AZu x BZu or BiK x Eu x BZu contains the Aljt representation. It is a simple matter to show that the first one is equal to AlK while the second is equal to Eg. Thus, the <5— S transition is electric-dipole allowed with z polarization and forbidden for radiation with its electric vector in the xy plane. 

Thus, the Alg — Blu and both of the Alg Biu transitions are electric dipole allowed. In all cases (see Fig. 7.2) the transitions are in-plane polarized, the first one occurring by absorption of radiation with its electric vector vibrating along the y or short axis of the molecule, the other two having x or long-axis polarization. 

The definitive resonance Raman spectra obtained by Clark and Franks for [(C4H,)4N] 2Re2Cl8 and [(C4H,)4N]2Re2Br8 were particularly informative (49). The observation of resonance enhancement in the Raman spectrum recorded with excitation frequencies in the range of the lowest electronic absorption near 14,000 cm 1 not only provided useful vibrational data, but also confirmed that this electronic absorption was electric dipole allowed in accord with the S- 5 assignment. Normal Raman spectra were obtained with excitation energies differing substantially from the absorption maximum near... 

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