Multiplet narrow

The quantum theory of spectral collapse presented in Chapter 4 aims at even lower gas densities where the Stark or Zeeman multiplets of atomic spectra as well as the rotational structure of all the branches of absorption or Raman spectra are well resolved. The evolution of basic ideas of line broadening and interference (spectral exchange) is reviewed. Adiabatic and non-adiabatic spectral broadening are described in the frame of binary non-Markovian theory and compared with the impact approximation. The conditions for spectral collapse and subsequent narrowing of the spectra are analysed for the simplest examples, which model typical situations in atomic and molecular spectroscopy. Special attention is paid to collapse of the isotropic Raman spectrum. Quantum theory, based on first principles, attempts to predict the. /-dependence of the widths of the rotational component as well as the envelope of the unresolved and then collapsed spectrum (Fig. 0.4). 

The combination of cross polarization (basically a pulse sequence) and MAS is sufficient to drastically reduce the linewidths of spin-Vi nuclei. Liquid-state proton NMR spectra, as we have seen, are characterized by extremely narrow lines and complex multiplets due to spin-spin coupling in addition, the normal chemical shift range is only around 10 ppm. 

Therefore, ionization events occurring at lower I.P. appear more interesting since they involve the d-type metal-centered orbitals and correspond to the dn configurations in the ligand-field splitting patterns appropriate to the molecular symmetry of M(CO)n, Thus we have one ionization band with multiplet structure, at 7.52 and 7.88 eV, from the t%g configuration of octahedral V(CO)6 (21), one narrow band at 8.42 eV from in octahedral Cr(CO)6 (22), two bands of equal intensity at 8.60... 

Dysprosium activated minerals have liuninescence in the visible part of the spectrum. The spectra of Dy + in minerals are mainly characterized by narrow fines near 480 and 575 nm, accompanied by the weaker ones near 660 and 752 nm corresponding to transitions from level F j2 to the levels of multiplets Hj and (Tarashchan 1978). Consequently, the spectra are not changed with delay time and excitation energy and all luminescence fines of Dy " are characterized by decay time. The best excitation at 350 nm is connected with 4/-4/ ffi5/2- G7 2 transition. Such liuninescence is detected in... 

However, no fingerprint such as a final state multiplet structure, as expected for fully localized 5 f electron and found in Am metal, is observed. The localization of 5 f-states is only weak (band-narrowing and widthdrawal from hybridization) in 6-Pu. This in fact is also consistent with the absence of a magnetic moment formation in 6-Pu (rather, a spin-fluctuation regime is observed ). 

The 13C NMR spectrum of acetone shown in Fig. 1.10(a) was obtained by proton decoupling. For the two nonequivalent nuclei two sharp singlets are observed. If proton decoupling is not applied, a proton-coupled 13C spectrum is obtained, and both 13C signals of acetone split into multiplets as shown in Fig. 1.10(b). A large quartet is found for the methyl carbons, which are each directly bonded to three protons with /H = f The signal of the carbonyl carbon atom, which is separated from six hydrogen atoms by two bonds, splits into a narrow septet. 

For off-resonance decoupling of 13C NMR spectra, frequency offsets of about 0.5 1 kHz are used. In order to avoid complete collapsing of multiplets by large, noise-modulated frequency bands, non-modulated decoupling fields are usually applied. The decoupling frequency offset can be adjusted until the multiplets are so narrow that no or only slight overlapping occurs. 

The structural assignment of the trithiepines 44-46 has been performed using H, 13C, heteronuclear multiple bond correlation (HMQC), heteronuclear multiple quantum correlation (HMBC), and variable-temperature NMR spectroscopic data. The 60MHz H NMR spectrum of trithiepine 44 exhibits a broad singlet at 3.05 ppm in CDC13, whereas a narrow ABCD multiplet was observed for all of the protons in a 300 MHz spectrum. The two 13C NMR signals at... 

D HMQC 33S/19F correlation spectra of SF6 have been reported. The spectra were acquired at 11.7 T, on a gas sample at high pressure24 (approximately 20 atm, T — 298 K) and on SF6 dissolved in thermotropic liquid crystals.25 At present, 33S 2D NMR does not seem to have great prospects for future development. SF6 is the only molecule in which 33S is strongly coupled to another nucleus (1/s—f — 250 Hz ca.) and shows a multiplet with very narrow line widths (1 Hz ca. in pure liquid). 

The effects of cross correlation can be exploited as a rich source of information on molecular dynamics by measuring relaxation behavior as a single line of a spin multiplet is perturbed. In addition, experiments can be designed to take advantage of the partial cancellation of relaxation effects and thus to obtain narrower lines than might otherwise occur. For example, in two-dimensional NMR it has been possible to utilize the quadratic dependence of CSA on B0 to... 

Andrew ER (1971) The narrowing of NMR spectra of solids by high-speed specimen rotation and the resolution of chemical shift and spin multiplet structures of solids. Prog NMR Spectrosc 8 1-39... 

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