Spin multiplet

The only electronic states that can be treated are those that correspond to the highest spin multiplet of a given orbital configuration. 

The basic INEPT spectrum cannot be recorded with broad-band proton decoupling, since the components of multiplets have antiphase disposition. With an appropriate increase in delay time, the antiphase components of the multiplets appear in phase. In the refocussed INEPT experiment, a suitable refocusing delay is therefore introduced that allows the C spin multiplet components to get back into phase. The pulse sequences and the resulting spectra of podophyllotoxin (Problem 2.21) from the two experiments are given below ... 

Any set of energetically well-isolated levels can be described by an effective spin Hamiltonian operator by choosing S to match the corresponding number of levels. This can be just one isolated Kramers doublet of a high-spin multiplet if the... 

C NMR spectra. The last group of problems (311-332) are of a different type and deal with interpretation of simple NMR spin-spin multiplets. To the best of our knowledge, problems of this type are not available in other collections and they are included here because we have found that the interpretation of multiplicity in H NMR spectra is the greatest single cause of confusion in the minds of students. 

This contribution will describe the manipulation of spin multiplets as a whole, and the word selective - or soft - will be used for multiplet-selective pulses, in contrast to band-selective, which refers to a broader bandwidth which may affect several spins, and to transition selective when only one line is affected. The discussion will be based on proton spectra, but all aspects are similar for other nuclei. Soft pulses use lower amplitudes and much longer irradiation times than non-selective hard pulses. Typical durations for soft pulses are of the order of 1 to 500 ms with a peak amplitude... 

The center of mass (CM) translational energy distribution curve (P(Ef) versus Erp) derived from T0F measurements of the Br atom produced in the 193 nm photolysis of bromoacetylene has three peaks. They occur at Erj, of 75, 40, and <20 kJ/mol. The first two peaks have about the energy difference associated with the spin-multiplet splitting in Br and suggest that the following primary processes occur at 193 nm ... 

As seen in Section 1.6, this approximation holds when the spin multiplet ground state is well isolated from excited electronic states, and ZFS is negligible. If 5 = lh, the g values can easily be measured through EPR spectroscopy and the g directions can be determined by single-crystal EPR measurements. When the latter measurements are not available, sometimes the principal g directions can be guessed from the symmetry of the molecule, and an independent estimate of the pseudocontact shift can still be attempted. 

In wide-band proton decoupled spectra complete proton decoupling is achieved and all carbon resonances appear as singlets. Enhancement of the 13C signals is observed as a result of the NOE and collapse of the C-H spin multiplets. 

Next we deal with the nature of the correction Awc. The resonance signals in a spectrum may be composed of overlapping, closely spaced components. Usually this is caused by either weak spin-spin couplings (we consider here only those which are included explicitly in the assumed model of an exchanging spin system) or by almost degenerate transitions in the spin multiplets. (81) Such effects should be compensated for by the correction Awc which can be determined from measurement of an apparent line-width, wa, in a theoretical spectrum calculated for a reasonably assumed value of the natural line-width, wtheor The correction (wa — wtheor) is virtually independent of the value... 

Rapid exchange is occurring at room temperature in methylene chloride or toluene solutions of trimethyl- or triethylthallium as evidenced by the collapse of the 205T1, 203T1, — H spin-spin multiplets, seen at —60° to —100° C, upon increase in the temperature. This exchange is concentration-... 

Electron paramagnetic resonance spectroscopy, also known as electron spin resonance (ESR) spectroscopy, detects the excitation of electron spins in an applied external magnetic field.13 Conventional continuous-wave (CW) EPR is based on resonance of a fixed-frequency standing microwave to excite some of the electrons in Zeeman-split spin multiplets to undergo a transition from a lower Ms level to a higher... 

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