Inverted fine structure

The most characteristic spectral detail for AM -diazetines is the fine structure in the UV spectrum around 350 nm. This is not typical, as other cyclic azo compounds usually show unstructured broad absorptions at 360 nm (62JCS3276, 78TL2469, 75JOC1409>. The PE spectrum of the tetramethyl derivative is also unique and shows an inversion in the normal n+,Tr,n energy level for cyclic azo compounds with the tt and n + levels inverted (77JOC609). 

In tetrahedral and cubic symmetry, the crystal-field levels are inverted, giving a single orbital state lowest. For dl in an octahedral field, the 4F state also has the single orbital state lowest, so we would expect the d1 configuration in a tetrahedral or cubic field to behave in a similar fashion and fit the spin Hamiltonian given in Eq. (158) solved for S=f. For most of the examples listed in Table XV, the tetrahedral symmetry is not distorted so that D = E=0 and no fine structure is reported. The 5=f character of the spin state is revealed in these cases by the fact that Eq. (80) must be added to the spin Hamiltonian to explain the ESR results on d1 in tetrahedral and cubic fields (131). For Co2+ in Cs3CoCl5, D= —4.5 cm-1 (222) and in CdS, D > 2 cm-1 (223). 

The splitting of triplet terms of helium is unusual in two respects. First, multiplets may be inverted and, second, the splittings of the multiplet components do not obey the splitting rule of Equation (7.20). For this reason we shall discuss fine structure due to spin orbit coupling in the context of the alkaline earth atomic spectra where multiplets are usually normal and... 

Quantitative measurement shows about 11% of the monomer units to be inverted. The principal spectrum shows splitting into mm, mr, and rr triad resonances with some pentad fine structure. The polymer is nearly atactic. Assignment of inversion "defect" resonances is made easier by reference to spectrum (b), which is that of poly (vinyl fluoride) prepared by the following route (17) ... 

In Chap. 7 we have discussed how hyperfine structure can be determined by level-crossing spectroscopy. Clearly, alkali atom states can readily be studied using this technique after step-wise excitation. We will here instead choose an example illustrating fine-structure measurements. In Fig.9.17 the example of the inverted sodium 4d 05/2,3/2 given. 

The challenge to experimentalists is to devise new techniques for spin-oibit state-selective study of other classes of atoms, most notably OPP) and otiier group VIA atoms. It is interesting to note that the 0(3p) fine-structure splittings [12] are very close (but inverted) to those for Ca( P ), for which significant spin-orbit effects have already been found. 

Fine-Structure Constants. Analysis of 115 transitions in the P, Q, and R branches of the fundamental band of NH" [7], [10, p. 85] and of 52 Q- and R-branch transitions in the fundamental band of NH" [6], [10, p. 85] gave the spin-orbit coupling constants A for the lowest vibrational levels v = 0 and 1 of the inverted electronic ground state X rij. Slightly higher are the values derived in the first study of the fundamental vibration-rotation spectrum of " NH" (48 R-branch transitions) by autodetachment spectroscopy [3]. The following results were obtained ... 

More recently, Funfachilling et al. have described another new short-pitch but U-uabk ferroelectrk Sc (SBF) configuration, which requires materials with a shoil pitch (p 0.4 pm) and large qxmtaneous polarization > 60 nOcm [5738]. The proMk SBF structure, which is not yet completely clear, is modified by an electrk field to an "inverted chevron structure, whkh appears between crossed polarizers as a pattern of fine black-and-white stripes if one polarizer is set parallel to the optical axis within one stripe. Contrary to the SSFLC structure, the chevrons are arranged in the substrate plane... 

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