Electronic spectra review

Initiated by the pioneering work of Burawoy [51 ], a number of experimental and theoretical studies were performed on the carbonyl group [52-55]. A complete review is beyond the scope of this paper. We will mention only some of them that we consider of particular importance for a comprehensive coverage of the electronic spectrum of formaldehyde for both the theoretical and experimental points of view. 

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]. 

Spectra of AH2 Molecules.—(i) Spectrum of H20. In the ground state of the H20 molecule all the orbitals represented in the Figure are fully occupied. These are the only low-lying orbitals of the molecule. No electronic spectrum of H20 is therefore expected until comparatively short wave-lengths are reached. In agreement, the first absorption of the molecule occurs as a continuum between 1830 and 1500 A (W ca. 1675 A Hopfield, Phys. Review, 1950, 77, 560). 

Surface electromagnetic waves or surface polaritons have recently received considerable attention. One of the results has been a number of review articles1, and thus no attempt is made here to present a comprehensive review. These review articles have been concerned with the surface waves, per se, and our interest is in the use of surface electromagnetic waves to determine the vibrational or electronic spectrum of molecules at a surface or interface. Only methods using optical excitation of surface electromagnetic waves will be considered. Such methods have been the only ones used for the studies of interest here. 

More recently, the CASSCF/CASPT2 method with spin-orbit coupling has been applied to a number of problems in actinide chemistry. Some recent examples are the electronic spectrum of U02 [38], the electronic structure of PhUUPh [62], the diactinides Ac2, Th2, Pa2, and U2 [36, 37], etc. Some of this work has recently been reviewed [63]. 

As an illustration of the current state of the art for electronic spectroscopy of transition metal ions in zeolites, refer to the recent review by Schoonheydt of Cu2+ in different zeolites [56]. Schoonheydt shows that experimental measurement of diffuse reflectance spectra (and in the case of Cu2 + EPR spectra) must be combined with theoretical calculations if a complete interpretation is to be made. The exact frequencies of the d-d transitions in the electronic spectrum of Cu2+ are independent of the zeolite structure type, the Si Al ratio, and the co-exchanged cations, but depend solely on the local coordination environment. Figure 20 shows the diffuse reflectance spectrum of dehydrated Cu-chabazite the expanded portion reveals the three d-d transitions in the region around 15000 cm l. 

NAD. The several possibilities for Zn -NAD interaction have been reviewed. However, the wide range of techniques that have been applied have failed to give conclusive evidence for direct metal-coenzyme interaction. Many studies have been inconclusive or contradictory. On the other hand there is some positive evidence for the maintenance of a four-coordinate geometry for the metal in the binary complex. Thus the shape and intensity of the electronic spectrum of Co(c)2Zn(n)2-LADH (discussed below) are consistent with the expected tetrahedral structure for the catalytic metal ion. However, there are no major changes in the spectrum of the binary complex, suggesting that the four-coordinate structure is maintained and that the coenzyme does not bind to the metal. 

The K shell has been omitted.) These authors summed up all the existing knowledge about the electronic spectrum of ethylene up to 1969 their extensive review is still highly informative. 

The spectroscopy and photochemistry of the [Co(CN)6] ion have been studied extensively and have been reviewed. Bands at 312, 260 and 202 nm in the electronic spectrum of aqueous solutions are assigned to the Tig, Tig and CT transitions respectively, and similar spectro-... 

Considerable information is available on the electronic spectrum of the ammonia molecule (see Fig. 3.3.1) and the principal findings have been reviewed by Robin In its ground state, the electronic configuration of NH3 may be expressed... 

Quantum chemical calculations on the electronic spectrum of compounds are generally carried out by separate calculations on the ground state and on each excited state. Most of the initial calculations on thiophene have been carried out by the PPP method, although calculations by CNDO and INDO have also been done. Results obtained prior to 1981 are discussed in detail in the review by Henriksson-Enflo <85HC(44/l)215>. 

Perhaps the most significant theoretical advance in LFT arose out of the Gerloch group during the late 1980s culminating in a comprehensive review published in 1997. It concerned one of the most basic properties of the electronic spectrum which hitherto had not been readily calculable namely the transition intensities. 

Stankevich IV, Nikerov MV, Bochvar DA, The structural chemistry of crystalline carbon geometry, stability and electronic spectrum, Russian Chemical Reviews, 53 640, 1984. 

The vibrational analysis of the highly structured 2600 A absorption system is of course one of the classic tales of spectroscopy, and it is told with superb clarity in two reviews. Suffice it to say that the initial analysis of Sponer, Nordheim, Sklar, and Teller, the further extensive work of Ingold and co-workers, and most recently the rotational analysis of the electronic spectrum by Callomon, Dunn, and Mills link this transition firmly with the state. The last-mentioned work now provides the most precise value of the forbidden electronic origin (the 0,0 band) of the transition. The origins are at 38,086.1 cm for C Hs vapor and 38,289 cm- for CeDg vapor. 

A book (B-71MS) and a review by Nishiwaki (74H(2)473) contain much information about the behaviour of pyrazoles under electron impact. The Nishiwaki review covers mainly the hydrogen scramblings and the skeletal rearrangements which occur. One of the first conclusions reached was that pyrazoles, due to their aromatic character, are extremely stable under electron impact (67ZOR1540). In the dissociative ionization of pyrazole itself, the molecular ion contributes about 45% to the total ion current thus, the molecular ion is the most intense ion in the spectrum. 

This review will endeavor to outline some of the advantages of Raman Spectroscopy and so stimulate interest among workers in the field of surface chemistry to utilize Raman Spectroscopy in the study of surface phenomena. Up to the present time, most of the work has been directed to adsorption on oxide surfaces such as silicas and aluminas. An examination of the spectrum of a molecule adsorbed on such a surface may reveal information as to whether the molecule is physically or chemically adsorbed and whether the adsorption site is a Lewis acid site (an electron deficient site which can accept electrons from the adsorbate molecule) or a Bronsted acid site (a site which can donate a proton to an adsorbate molecule). A specific example of a surface having both Lewis and Bronsted acid sites is provided by silica-aluminas which are used as cracking catalysts. 

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