Electronic spectra intensities

Fig. VIII-10. (a) Intensity versus energy of scattered electron (inset shows LEED pattern) for a Rh(lll) surface covered with a monolayer of ethylidyne (CCH3), the structure of chemisorbed ethylene, (b) Auger electron spectrum, (c) High-resolution electron energy loss spectrum. [Reprinted with permission from G. A. Somoijai and B. E. Bent, Prog. Colloid Polym. ScL, 70, 38 (1985) (Ref. 6). Copyright 1985, Pergamon Press.]...

In addition to total energy and gradient, HyperChem can use quantum mechanical methods to calculate several other properties. The properties include the dipole moment, total electron density, total spin density, electrostatic potential, heats of formation, orbital energy levels, vibrational normal modes and frequencies, infrared spectrum intensities, and ultraviolet-visible spectrum frequencies and intensities. The HyperChem log file includes energy, gradient, and dipole values, while HIN files store atomic charge values. 

Scaiano and Kim-Thuan (1983) searched without success for the electronic spectrum of the phenyl cation using laser techniques. Ambroz et al. (1980) photolysed solutions of three arenediazonium salts in a glass matrix of 3 M LiCl in 1 1 (v/v) water/acetone at 77 K. With 2,4,5-trimethoxybenzenediazonium hexafluorophos-phate Ambroz et al. observed two relatively weak absorption bands at 415 and 442 nm (no e-values given) and a reduction in the intensity of the 370 nm band of the diazonium ion. The absence of any ESR signals indicates that these new bands are not due to aryl radicals, but to the aryl cation in its triplet ground state. 

The electronic spectrum of S2O has been studied both in absorption and in emission and both in the ultraviolet and the visible regions. The absorption spectrum in the near UV region is extremely intense and well suited to detect S2O in gases even at very low partial pressures. Two band systems are located in the UV region at 340-250 nm and at 230-190 nm [35] while a third system in the visible region at 645-575 nm was discovered only by op-toacoustic detection [36]. The 340-250 nm system has also been observed for matrix-isolated S2O [37]. For more details see [1, 38-47]. 

It is seen from the electron spectrum that a TBSM — MA copolymer absorbs in the UV region within a wide range (190-240 nm) with a maximum at X = 205 nm while the sensitizer absorbs in both the UV (250-280 nm,X = 260 nm) and 360-420 nm region with two maxima at 380 and 415 nm. Irradiation of the copolymer results in a lower intensity maximum at k = 205 nm which indicates the occurrence of photochemical reactions. 

In ideal situations, optical spectroscopy as a function of temperature for single crystals is employed to obtain the electronic spectrum of a SCO compound. Knowledge of positions and intensities of optical transitions is desirable and sometimes essential for LIESST experiments, particularly if optical measurements are applied to obtain relaxation kinetics (see Chap. 17). In many instances, however, it has been demonstrated that measurement of optical reflectivity suffices to study photo-excitation and relaxation of LIESST states in polycrystalline SCO compounds (cf. Chap. 18). 

The stability of C60 and C70 solutions in vegetable oils has been examined also towards the action of UV light. A C60 solution in linseed oil has been irradiated in a quartz reactor with UV light from a 12 W low-pressure Hg lamp having its main emission at 254 nm under N2. In less than 1 hour irradiation, all the visible part of the electronic spectrum of C60 with bands at about 530 and 600 nm have been bleached. Simultaneously, a growth in absorption intensity as function of the irradiation time has been observed at about 410nm. 

For a 1 the scattered light spectrum is gaussian with a width determined by the electron temperature, because it is due to the incoherent sum of Thomson scattering from individual, thermally moving electrons. The intensity and spectral linewidth of scattered light therefore yield electron density and temperature. 

The question then remains as to why the relaxivity is relatively high for ions whose ground state does not have an S configuration. An inversion between the H4g and Eog states as suggested by Glebov et al. (42) appears unlikely in view of recent theoretical investigations of the absorption frequencies and intensities in the electronic spectrum of NpO (38,41). An admixture of states is more likely as Matsika et al. (38) found that the ground state of NpO is only 84% H4g (5u< )i,) and as Ismail et al. (40)... 

The resonance Raman enhancement profiles In Figures 7 and 8 show that the maximum Intensity of the Fe-O-Fe symmetric stretch falls to correspond to a distinct absorption maximum In the electronic spectrum. This Implies that the 0x0 Fe CT transitions responsible for resonance enhancement are obscured underneath other, more Intense bands. Although strong absorption bands In the 300-400 nm region (e > 6,000 M" cm"l) are a ubiquitous feature of Fe-O-Fe clusters, the Raman results make It unlikely that they are due to 0x0 -> Fe CT. An alternative possibility Is that they represent simultaneous pair excitations of LF transitions In both of the... 

Electronic spectra (Table 1.1, Fig. 1.2) have been measnred for the orange soln-tions of (RuO ] in aqueous base from 250-600 nm. [212-215, 222], and reproduced [215, 222]. There are two at 460 and 385 nm. [212, 213, 222] or three bands in the visible-UV region, at 460, 385 and 317 nm [214, 215]. These appear to be at the same positions as those for [RuO ] but the intensities and hence the general outline of the two spectra are very different. Woodhead and Fletcher reviewed the published molar extinction coefficients and their optimum values / dm (mol" cm" ) are 1710 for the 460 nm. band, 831 for the 385 nm. band and 301 for the 317 nm. band - the latter band was not observed by some workers [214]. The distinctive electronic spectrum of ruthenate in solution is useful for distinguishing between it, [RuO ]" and RuO [212, 222]. Measurements of the electronic spectra of potassium ruthenate doped in K CrO and K SeO and of barium ruthenate doped into BaSO, BaCrO, and BaSeO (in all cases the anions of these host materials are tetrahedral) indicate that in that these environments at least the Ru is tetrahedrally coordinated. Based on this evidence it has been suggested that [RuO ] in aqueous solution is tetrahedral [RuO ] rather than franx-[Ru(0H)3(0)3] [533, 535]. Potential modulated reflectance spectroscopy (PMRS) was used to identify [RuO ] and [RuO ] " in alkaline aqueous solutions during anodic oxidation of Ru electrodeposited on platinum from [Ru3(N)Clg(H30)3] [228]. 

Alexander and Gray 70) and Caulton 71) have studied the electronic spectrum of the species [Co(CN)5] . Although direct proof is lacking, it has been affirmed that the optical and E. P. R. spectra are consistent with an essentially square p5u-amidal stereochemistry and are inconsistent with a trigonal bipyramidal structure (70). It has been claimed, however, that this species may be actually six-coordinate in water, i. e. [Co(CN)5(H20)]3- (72). The spectrum of [Co(CN)5]3. has four bands of low intensity between 10 and 32 kK, as well as two high intensity bands at higher frequence (Table 7). 

Fig. 15. Angle-integrated photoelectron energy distribution curves of uranium in the region of the giant 5 d -> 5 f resonance (90 eV < hv < 108 eV). The 5 f intensity at Ep is suppressed by more than a factor of 30 at the 5 ds/2 threshold (see the spectra for hv = 92 and 94 eV) and resonantly enhanced above threshold (see, e.g., the spectrum for hv = 99 e V). At an initial energy 2.3eV below Ep a new satellite structure is observed which is resonantly enhanced at the 5 d5/2 and 5 ds onsets. At threshold the satellite coincides with the Auger electron spectrum, which moves to apparently larger initial energies with increasing photon energy (from Ref. 67)...

The first 5-membered Meisenheimer-type adduct was obtained from 2-methoxy-3,5-dinitrothiophene (121 X = OMe, Y = Z = NOz) by reaction with methoxide ion in methanol.16,55 The sodium (or potassium) salt can be isolated as a deep purple solid whose elemental analysis is consistent with the formation of a 1 1 adduct. The IR spectrum is characterized by the presence of strong bands in the 1000-1250 cm"1 region, where geminal dialkoxy adducts23 usually exhibit strong absorption. The electronic spectrum shows intense absorption at 312 and 532 nm, which accounts for the red color of the methanol solution. 

A complex closely related to those possessing an Mo203 4+ core is [Mo20(Ntol)2(S2CNEt2)4] (tol = 4-tolyl), prepared by reducing [MoO(Ntol)(S2CNEt2)2].142 IR and 170 NMR studies have indicated an oxo-bridged structure for the dimer there is an intense absorption at 18760 cm-1 in the electronic spectrum, which does not obey the Lambert-Beer law due to a disproportionation reaction which sets up an equilibrium with MoIV and MoVI species. 

The integrated intensity of the satellite spectrum is very close to that of the trapped electron spectrum. The former spectrum decays concomitantly with the latter either with photo-bleaching with the infrared... 

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