Electronic spectra, theoretical

Heilbronner, E., Weber, J.P., Michl, J., and Zahradnik, R., The electronic spectra of acenaphthylene and fluoranthene. A comment on the classification of electronic spectra, Theoret. Chim. Acta, 6, 141, 1966. 

The electronic spectrum of the radical has been recorded long before a satisfactory theoretical explanation could be provided. It was realized early on that the system should be Jahn-Teller distorted from the perfect pentagon symmetry (D5/, point group). Recently, an extensive experimental study of the high-resolution UV spectrum was reported [76], and analyzed using Jahn-Teller formalism [73],... 

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. 

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. 

Lorentzon J, Fiilscher MP, Roos BO (1995) Theoretical study of the electronic spectrum of uracil and thymine. J Am Chem Soc 117 9265... 

Mi CO). The first metal-metal bond to be characterized (35) is the formally single Mn-Mn bond in Mi CO). This compound has often been used as the model for developing electronic structure theories (1.18.36.37). Extremely efficient photofragmentation is responsible for the structureless electronic spectrum and the lack of emission following excitation of this molecule. This spectroscopic deficiency necessitates photofragmentation studies to obtain data to verify theoretical models. Most of the photochemical experiments in the past explored the reactions of the lowest excited singlet state in the near ultraviolet. 

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 physical characteristics reported for 5 are striking, especially in their seemingly close relationship to those observed for the protein oxy-Hc. The Cu...Cu distance in 5, its diamagnetism (normal H NMR Evans susceptibility), and the electronic spectrum with 349 ran (8 = 21,000) and 551 ran (8 = 800) bands closely resemble the properties of oxy-Hc. The particularly low value (even for peroxide) of the O—O stretch of 741 cm1 (resonance Raman) in 5 also matches corresponding values seen in oxy-Hcs (—750 cm-1) this latter property has been accounted for in theoretical studies [110], which show that the unoccu-... 

The failures of the Born-Oppenheimer separation of the electronic and nuclear motions show up in the spectra of molecules as homogeneous or heterogeneous perturbations in the spectra41. See, e.g. Ref. (42) for an example, a fully ab initio study of the spectrum of the calcium dimer in a coupled manifold of electronic states. Theoretical methods needed to describe the dynamics of molecules in nonadiabatic situations are being developed now. See Ref. (43) for a review. 

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... 

A theoretical treatment of 1,2-oxathietane indicates planarity with aS-0 bond length of 1.669 A and a C-S-0 angle of 100.6°. The electronic spectrum was calculated. The character of the HOMO is largely that of the sulfur 3p orbital. A CNDO molecular orbital study of the retrocycloaddition of 1,2-oxathietane 2-oxide to sulfur dioxide and ethylene shows that strong heteroatom asymmetry lifts the stereoelectronic requirement that the thermal fragmentation occur by a suprafacial-antarafacial path. ... 

A. Borin-Carlos, M.H.M. Olsson, U. Ryde, B.O. Roos, E. Cedergren-Zeppesauer A. Merli (2000) A theoretical study of the structure and electronic spectrum of Cu-substituted alcohol dehydrogenase , J. Am. Chem. Soc. submitted. 

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. 

Negative Results on HOg. Perhaps the most interesting, puzzling, and somewhat frustrating series of negative results carried out in our laboratory (15) concerns the search for the free radical HO2. The techniques discussed above have been so very successful in the study of labile molecules that any one of them would be expected to yield trapped HO2. There are theoretical reasons (43, 49) why HO2 is expected to have an electronic spectrum in the visible or photographic infrared. Certainly such predictions that are found to be valid for all known flrst-row triatomic molecules are not expected to fail in the case of HO2. 

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