Spectroscopy multiplet structure

A resonance in NMR spectroscopy is generally characterized by five parameters, the chemical shift (8), the intensity or the area of the resonance (proportional to concentration), the multiplet structure [related to the spin-spin coupling constant (J)], and two relaxation... 

During the meeting, various applications of and perspectives on the DV-Xa method were discussed in detail. Among them, the usefulness of theoretical analysis using DV-Xa calculation for X-ray and electron spectroscopy such as XPS, XES (X-ray emission spectroscopy), XANES, ELNES, and AES was presented and discussed. A new universal computational method for the many-electron-state, DV-ME (DV-multielectron) method was introduced by demonstrating its advantages and possibilities for application to the calculation of the multiplet structure of the d-d transition in various transition metal oxides. Another topic was the application of the DV-Xa method to materials science. The study of... 

Andrew, E. R. (1972). The narrowing of NMR spectra of solids by high speed specimen rotation and the resolution of chemical shift and spin multiplet structures of solids. In Progress in NMR Spectroscopy, Vol. 8, Pt. 1 (J. W. Emsley, J. Feehez, and L. H. Satcliffe, eds.). Pergamon, New York, pp. 1-39. 

The DEPT experiment [33] (Distortionless Enhancement by Polarisation Transfer) is the most widely used polarisation transfer editing experiment in carbon-13 spectroscopy, although its application is certainly not limited to the proton-carbon combination. It enables the complete determination of all carbon multiplicities, as does the refocused INEPT discussed above, but has a number of distinct advantages. One of these is that it directly produces multiplet patterns in proton-coupled carbon spectra that match those obtained from direct observation, meaning methylene carbons display the familiar 1 2 1 and methyl carbons the 1 3 3 1 intensity patterns this is the origin of the term distortionless . However, for most applications proton decoupling is applied during acquisition and multiplet structure is of no consequence, so the benefits of DEPT must lie elsewhere. 

These theorems are further discussed in [21]. They show that, in the independent electron approximation, we can think, not only of independent electrons, but also of independent vacancies, which behave like electrons and even give rise to very nearly the same multiplet structure. This simplifies X-ray spectroscopy enormously, and further emphasises the significance of closed shells. 

These elements possess well-developed multiplet structure in the soft X-ray spectra of the condensed phase, which can be compared with the spectrum of the free atom by performing ah initio Dirac-Fock calculations, the actual 4/ occupancy in the solid can be deduced. An example is shown in fig. 11.4 The first point to note is that the multiplet structure of the atom survives in the solid, because of the strong localisation of the 4/ electrons (see section 5.6), so that soft X-ray spectroscopy provides a... 

An example of such spectra is shown in Fig. 16 (n-hexane). The traces plotted for various values of co how that parallel to the coj-axis, the full multiplet structure is retained whereas in the coj direction the completely decoupled spectrum results. The undecoupled spectrum is to be considered as a projection of the spectra for various values of onto the coj-axis. This rather involved technique is less sensitive than ordinary FTNMR. It has been used mainly in C-NMR spectroscopy. A number of applications as well as the solution to problems connected with this method have been reported -307>... 

Core-level spectroscopies are the appropriate tools to study the electronic distribution around free atoms and the changes induced in this distribution on condensation or on the formation of compounds involving other elements. These spectroscopies are also very useful to track the formation of clusters which finally coalesce to form well-defined solid phases. For the R, X-ray absorption spectroscopy is very useful because of the simplicity of the final multiplet structure, as the transitions obey dipole selection rules. Generally, two types of transitions are observed one in which the 4f electron participates in the transition and another in which it remains as a spectator. In the former case, a transition of a d electron to the empty f shell is involved. This leads to the formation of the nd 4f - d 4f + ( = 3,4) multiplets which are in fact finger prints of the R atom configurations. In the same way, the transitions from p levels scan the empty sd states of the conduction band. 

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. 

The f-count determination of ICF compounds at the beginning of the rare earth series in CEELS is therefore hampered by final-state effects as in other core level spectroscopies. In comparison to XAS CEELS shows further complications as a result of more complicated final-state multiplet structure (Strasser et al. 1983b, Hillebrecht et al. 1986). However, Schneider et al. (1985) have included recently analysis of 3d CEELS of La and Ce compounds with fractional f occupation into the many-body formalism of an Anderson impurity model. The agreement of relative energy positions between calculated and measured spectra was encouraging, but in order to assess fully the consequences of initial-state mixing in the final state, multiplet splitting has to be included into the many-body formalism. 

G.A. Morris, Indirect two-dimensional J spectroscopy measurement of proton multiplet structure via carbon-13 signals, J. Magn. Resonance 44, 277 (1981). 

This multiplet structure weakens the signal for the spectra and, in the case of many resonances, complicates the spectra beyond recognition. For C solution NMR spectroscopy it is desirable to eliminate the multiplet fine structure arising from the J coupling of the carbons to the protons. Spin decoupling causes the vectors of a multiplet to be static in the rotating frame because their Larmor frequencies become... 

Two-dimensional spectroscopy should not be dismissed as merely an alternative (and quite complicated) display mode, for it has some inherent operating advantages. The first is the possibility of disentangling spectra that are complicated by extensive and multiple overlapping of spin-multiplet structure — the problem that eventually makes very large molecules intractable for NMR. — G. Bodenhausen et al. [57]... 

---