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Laporte selection rule intensities

The only positively identified magnetic dipole transition at room temperature so far is the 7Fo Di transition in Eu3+ at 5250 A. The abscence of centrosymmetry in crystal allows the changes in J and L upto seven units due to admixture of states (through sixth order terms) giving rise to weak electric dipole transition. The weak intensities of the intra f—f transition can be accounted for by the Laporte selection rule. [Pg.148]

Intensities of absorption bands are governed by probabilities of electronic transitions between the split 3d orbital energy levels. The probabilities are expressed by selection rules, two of which are the spin-multiplicity selection rule and the Laporte selection rule. [Pg.65]

Finally, in deriving structural information from the features of d-d spectra of TMls, it must be considered that, because of the Laporte selection rule, ion sites with octahedral symmetry can contribute to the spectra only to a very limited extent, and so can escape spectroscopic detection. However, this behavior can be turned into a tool to monitor the distribution of TMIs in sites with different structure as a function of loading, as in the case of CoAPO zeotype materials. In this case, the attainment of a plateau level of the intensity of the d-d bands due to Co ions with tetrahedral symmetry that became inserted in the framework indicated the formation of extra-framework species, containing d-d silent octahedral Co sites with increasing loading (Figure 2.16) [77]. [Pg.75]

In general, tetrahedral complexes have more intense absorptions than octahedral complexes. This is a consequence of the first (Laporte) selection rule (Section 11-3-1) transitions between d orbitals in a complex having a center of symmetry are forbidden. As a result, absorption bands for octahedral complexes are weak (small molar absorptivi-ties) that they absorb at all is the result of vibrational motions that act continually to distort molecules slightly from pure symmetry. [Pg.406]

In tetrahedral environments the splitting becomes reversed the former orbitals, now of t2 symmetry, are lifted by 2/5 A and the former eg orbitals, now of e symmetry, are shifted downwards by 3/5 A, where At=Et2-Ee=4/9 A, (see Fig. 6). Upon lowering the symmetry of the environment the residual degeneracy is removed further as shown, e.g., for a square planar field. As there is no center of inversion, the Laporte selection rule is no longer valid resulting in an increased intensity of the electronic bands. [Pg.349]

In tetrahedral complexes, the situation is different. The lack of a center of symmetry means that the Laporte selection rule does not apply. The consequence is that tetrahedral complexes often have much more intense absorption bands than octahedral complexes. ... [Pg.429]

Kotzian (1991) and Kotzian et al. (1995) reported INDO/S-CI results for transition energies and relative oscillator strengths of the 4f—>4f excitations in the [R(H20) ] (R=Pr, Nd, Tm, n=8,9) complexes. These excitations are parity-forbidden for the free ion (Laporte selection rule), but may gain intensity due to admixture of opposite-parity character in a non-centrosymmetric environment The field of the water ligands leads only to a small perturbation of the free ion energy levels (Pr 4f, Nd 4f, Tm 4f ). Due... [Pg.702]

For an atom the dipole moment operator has inversion symmetry across the nucleus therefore the absorption integral is zero if both the electron wavefunctions are of the same parity, but non-zero if they are of different parity. Thus an s s orbital transition is forbidden , but s - p orbital transition is allowed . This is the Laporte selection rule (also known as the parity selection rule), perhaps the most commonly observed consequence of which is the low intensities of d-d transitions in transition metal complexes. By itself, the parity selection rule would suggest that an i -> / transition is allowed. However, consideration of conservation of angular momentum, restricts changes to those transitions in which A1 = 1. (The possibilities of an increase or decrease in / arise because of the vector nature of momenta, which can oppose or reinforce one another). [Pg.55]

The fact that many of the observed colours are of low intensity is consistent with the colour originating from electronic "d-d transitions. If we are dealing with an isolated gas-phase ion, such transitions are forbidden by the Laporte selection rule (eq. 19.4 where / is the orbital quantum number). The pale colours observed in complexes indicate that the probability of a transition occurring is low. Table 19.2 shows relationships between the wavelength of light absorbed and observed colours. [Pg.643]

A6.22 A [CoCU] ) tetrahedral complexes have more intense d-d transition due to partial breakdown of the Laporte selection rule. [Pg.132]

Laporte and spin-multiplicity selection rules ( 3.7) and have intensities 103 to 104 times higher than those of crystal field transitions (table 3.6), their absorption edges may extend well into the visible region and overlap crystal field spin-allowed and spin-forbidden peaks. [Pg.133]

Unless (v iG)spin = ( i E)spin. then the spin component is zero and the transition is spin-forbidden. Nevertheless, spin-forbidden transitions are observed as weak features (as in Fig. 2.18) typically with 10 -10 the intensity of fully allowed transitions. This is because of the interaction between the electron spin magnetic moment and the magnetic moment due to the orbital motion of the electron (spin-orbit coupling). The La-porte selection rule, furthermore, states that only transitions between wave functions with one having gerade and the other ungerade character are allowed (hence all d-d transitions are Laporte forbidden). This arises since the spatial component can be further broken down ... [Pg.41]

From a more practical point of view, electronic transitions follow two types of selection rules because of the orbital and spin nature of the electronic wavefunction. The first, called the Laporte rule, requires that A/ = + 1 for the orbitals involved in the transition. It predicts, for instance, that electronic transitions for transition metal ions in 7 d symmetry (involving orbitals with d-p character) should be more intense than Laporte-forbid-den d-d transitions in Oh symmetry involving orbitals of the same character thus leading to A/ 0. By contrast, charge-transfer transitions are essentially Laporte-allowed since they concern orbitals involving different atoms with different characters. In the case of centrosymmetric complexes, this rule implies a change of parity u u and g -> g transitions (as, for... [Pg.129]

The possibility of transition occurring is determined by spin selection rules ( transitions between different multiplicity terms are prohibited, e.g., singlet triplet) and the Laporte rule ( transition between terms of the same parity, g g and u —> u, are prohibited ). It is important to emphasize that a prohibited transition means that the possibility of it occurring was restricted and, therefore, its intensity is reduced. [Pg.243]


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See also in sourсe #XX -- [ Pg.72 ]




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