Electronic spectra 466 Subject

Indazoles have been subjected to certain theoretical calculations. Kamiya (70BCJ3344) has used the semiempirical Pariser-Parr-Pople method with configuration interaction for calculation of the electronic spectrum, ionization energy, tt-electron distribution and total 7T-energy of indazole (36) and isoindazole (37). The tt-densities and bond orders are collected in Figure 5 the molecular diagrams for the lowest (77,77 ) singlet and (77,77 ) triplet states have also been calculated they show that the isomerization (36) -> (37) is easier in the excited state. 

The electronic spectrum of free base porphin has been the subject of many experimental and theoretical studies. Because of the size of this molecule, obtaining meaningful ab initio calculations has been a significant challenge. Different calculations naturally give different numerical results, but they also give different... 

In Table 25 we present results of TDA and EOM-CCSD calculations for the ketene molecule. This system has an extraordinarily complex electronic spectrum, which has been the subject of a number of experimental and theoretical analyses. It also illustrates many features of excited state calculations. 

Aldehydes and ketones are important chromophoric groups, which play a central role in many different areas of chemistry. Formaldehyde is the prototype molecule for these kinds of compounds. Its electronically excited states have therefore been investigated extensively both experimentally and theoretically (see Refs. 63-65 and references cited therein). Acetone is the simplest aliphatic ketone. It is probably the best experimentally studied system of this group of important organic systems. The interpretation of its electronic spectrum has been and remains a subject of experimental interest [66-73]. In contrast to formaldehyde, acetone has been much less studied theoretically, undoubtedly due to the larger size of the molecule. To our knowledge there exist only two previous ab initio studies [74, 75]. Formaldehyde, on the other hand, is frequently used for testing new theoretical methods developed to treat excited states, because of its apparent simplicity and the numerous studies available. 

The reason for the delay is that a detailed discussion is slightly more complicated for electronic spectra than for rotations or vibrations. Some new ideas will have to be developed in order to begin to understand the electronic spectra and structures of many-electron systems. (We should recognize that the electronic spectrum of hydrogen, even in the formalism of quantum mechanics, will be relatively simple.) fiowever, as with rotational and vibrational spectroscopy, our treatment of electronic spectroscopy in this chapter is limited by necessity. Entire books are written on the subject, and we can only introduce some basic ideas here. 

Excitation spectra arise from transitions between different quantum states of the system, corresponding to different nondegenerate solutions of the Schrodinger equation. In quantum chemistry it is common practice to treat the solution of the Schrodinger equation within the Bom-Oppenheimer approximation [1] and separate the electronic and nuclear degrees of freedom. Consequently the excitation spectra are also separated into an electronic and a roto-vibrational spectrum. The former is studied mainly in optical (UV/vis) spectroscopy experiments and will constitute the main subject of this chapter the latter, which can be investigated by infrared, microwave or Raman spectroscopy measurements, provides fine-structure corrections to the electronic spectrum. 

The electronic spectrum of the blue [Cr(H20) ] solution has an absorption band with a maximum at 714 nm. The broadness of the band is expected for a d-d band for a high spin species of d configuration, subject to Jahn Teller distortion. (See Fig.A9.2). The titration can be performed electrochemically (Sec.2.5.1). 

There has been much discussion of the relative contributions of the no-bond and dative structures to the strength of the CT complex. For most CT complexes, even those exhibiting intense CT absorption bands, the dative contribution to the complex stability appears to be minor, and the interaction forces are predominantly the noncovalent ones. However, the readily observed absorption effect is an indication of the CT phenomenon. It should be noted, however, that electronic absorption shifts are possible, even likely, consequences of intermolecular interaetions of any type, and their characterization as CT bands must be based on the nature of the spectrum and the structures of the interaetants. This subject is dealt with in books on CT complexes. ... 

This technique can be applied to samples prepared for study by scanning electron microscopy (SEM). When subject to impact by electrons, atoms emit characteristic X-ray line spectra, which are almost completely independent of the physical or chemical state of the specimen (Reed, 1973). To analyse samples, they are prepared as required for SEM, that is they are mounted on an appropriate holder, sputter coated to provide an electrically conductive surface, generally using gold, and then examined under high vacuum. The electron beam is focussed to impinge upon a selected spot on the surface of the specimen and the resulting X-ray spectrum is analysed. 

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