Hyperfine sublevels

Hdfer P, Grupp A, Nebenfuhr H and Mehring M 1986 Hyperfine sublevel correlation (HYSCORE) spectroscopy a 2D ESR investigation of the squaric acid radical Chem. Phys. Lett. 132 279-82... 

Advanced EPR techniques such as CW and pulsed ENDOR, electron spin-echo envelope modulation (ESEEM), and two-dimensional (2D)-hyperfine sublevel correlation spectroscopy (HYSCORE) have been successfully used to examine complexation and electron transfer between carotenoids and the surrounding media in which the carotenoid is located. 

HexOMe, methyl glycoside Hex-onic, aldohexonic acid hmba, 2-hydroxy-2-methylbutanoate2 HYSCORE, hyperfine sublevel correlation spectroscopy mod. ampl., modulation amphtude polyGalA, galacturonan Qa, quinic acid XAFS, X-ray absorption fine structure spectroscopy... 

Firstly the degeneracy between hyperfine sublevels is removed by the Zee-man effect. 

There are many other specialized methods electron-electron double resonance (ELDOR), TRIPLE, HYSCORE (hyperfine sublevel correlation spectroscopy, which is similar to 2D-EPR), electron spin-echo, and so on these methods are not discussed here. 

DPPH = 2,2-diphenyl-1-picrylhydrazyl ENDOR= electron-nuclear double resonance EPR = electron paramagnetic resonance ESE = electron spin echoes ESEEM = electron spin echo envelope modulation EFT = fast fourier transformations FWHM = fidl width at half maximum HYSCORE = hyperfine sublevel correlation nqi = nuclear quadrupole interaction TauD = taurme/aKG dioxygenase TWTA = traveling wave tube amphfier ZFS = zero field sphtting. 

Continuous wave operation of COIL is facilitated by the hyperfine structure of the atom. Iodine has a nuclear spin of, so the P /2 and Pz/2 levels are split by hyperfine interactions. Figure 8 shows the allowed transitions between the hyperfine sublevels and a high resolution emission spectrum. The F = 3 — F" = 4 transition is most intense, and this is the laser line under normal conditions. Collisional relaxation between the hyperfine sub-levels of Pz 2 maintains the population inversion, while transfer between the Fi/2 levels extracts energy stored in the F = 2 level. Hence, if it is not sufficiently rapid, hyperfine relaxation can limit power extraction. 

Other pulse sequences are in use such as the three-pulse sequence (Figure 3.16) and hyperfine sublevel correlation (HYSCORE) spectroscopy, the latter being a two-dimensional technique.P ]... 

Resolved hyperfine structure (hfs) due to the interaction of optical electrons with the magnetic moment of the Pr nucleus (1=5/2) was observed in the spectra (Fig. 3).The measured hyperfine splittings and widths of hyperfine sublevels found from the experimental line shapes are presented in Table I. 

With the commercial availability of pulsed EPR instrumentation, other pulsed methods such as electron-spin echo envelope modulation (ESEEM) or hyperfine sublevel correlation spectroscopy (HYSCORE), which are quite useful to study specific hyperfine and quadrupolar couplings, have also been applied to flavoproteins [59, 61, 62]. These studies have been reviewed recently, e.g., in [46]. 

There are also pulse EPR methods that probe the chemical or rather magnetic environment. These are pulse electron nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopy, which allow measuring hyperfine couplings from the unpaired electron spin to surrounding magnetically active nuclei ([20] in Fig. 3 this is a P nucleus). As these experiments are performed in frozen solution (e.g., in all examples of this chapter) or in solids, from the anisotropy and orientation dependence of the hyperfine coupling one can obtain valuable information on the structure up to 1 nm. 

Abstract Multi-resonance involves ENDOR, TRIPLE and ELDOR in continuous-wave (CW) and pulsed modes. ENDOR is mainly used to increase the spectral resolution of weak hyperfine couplings (hfc). TRIPLE provides a method to determine the signs of the hfc. The ELDOR method uses two microwave (MW) frequencies to obtain distances between specific spin-labeled sites in pulsed experiments, PELDOR or DEER. The electron-spin-echo (ESE) technique involves radiation with two or more MW pulses. The electron-spin-echo-envelope-modulation (ESEEM) method is particularly used to resolve weak anisotropic hfc in disordered solids. HYSCORE (Hyperfine Sublevel Correlation Spectroscopy) is the most common two-dimensional ESEEM method to measure weak hfc after Fourier transformation of the echo decay signal. The ESEEM and HYSCORE methods are not applicable to liquid samples, in which case the FID (free induction decay) method finds some use. Pulsed ESR is also used to measure magnetic relaxation in a more direct way than with CW ESR. 

Overlap of lines can make analysis difficult when several nuclei contribute in the one-dimensional (ID) two- and three-pulse ESEEM spectra. Eollowing the development in NMR, methods to simplify the analysis involving two-dimensional (2D) techniques have therefore been designed. The Hyperfine Sublevel Correlation Spectroscopy, or HYSCORE method proposed in 1986 [14] is at present the most commonly used 2D ESEEM technique. The HYSCORE experiment has been applied successfully to study single crystals, but is more often applied to orienta-tionally disordered systems. It is a four-pulse experiment (Fig. 2.23(a)) with a k pulse inserted between the second and the third k/2 pulse of the three-pulse stimulated echo sequence. This causes a mixing of the signals due to the two nuclear transitions with m.s = Vi of an 5 = Vi species. For a particular nucleus two lines appear at (v , V ) and (V ", v ) in the 2D spectrum as shown most clearly in the contour map (d) of Fig. 2.23. The lines of a nucleus with a nuclear Zeeman frequency... 

As an example, Figure 14 shows the hyper fine spectrum of the D] line of sodium obtained 18 using this technique four components are visible, which are predicted between the two hyperfine sublevels (F = 0 and 1) of the ground level 3Si/2 hyperfine sublevels (F = 0... 

More elaborate pulse sequences have been designed to selectively extract specific information about a spin system. A particularly useful experiment for structural studies of metal complexes is the two-dimensional four-pulse experiment called HYSCORE, hyperfine sublevel correlation spectroscopy. The resulting two-dimensional plot reveals the correlation between different modulation frequencies arising from the same nucleus, which greatly facilitates assignment of frequencies in complicated spin systems. ... 

In Section 15.3.3, we discussed the excitation of higher electronic states using laser light to drive optical dipole transitions. The interaction was strongly damped by spontaneous emission from the upper level indeed, the molecules were detected by means of the scattered photons. In this section, we consider some ways to manipulate the hyperfine sublevels within the ground state of the molecule. In contrast to optical transitions, the coherences between these ground-state levels are not radiatively damped. 

---