Electronic experimental spectra

Sheves, M., Nakanishi, K., Honig, B. (1979). Through-space electrostatic effects in electronic spectra. Experimental evidence for the external point-charge model of visual pigments, J. Am. Chem. Soc., 101 7086. 

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],... 

The longest wavelength absorption transition for ethene calculated by HyperChem using PM3 is 207 nm, which compares favorably with the experimental value of 190-200 nm. After you compute an electronic spectrum with HyperChem, you can use the table below to assign computed transitions and qualitatively assess the accuracy of the computation. ... 

It is clear that an ah initio calculation of the ground state of AF Cr, based on actual experimental data on the magnetic structure, would be at the moment absolutely unfeasible. That is why most calculations are performed for a vector Q = 2ir/a (1,0,0). In this case Cr has a CsCl unit cell. The local magnetic moments at different atoms are equal in magnitude but opposite in direction. Such an approach is used, in particular, in papers [2, 3, 4], in which the electronic structure of Cr is calculated within the framework of spin density functional theory. Our paper [6] is devoted to the study of the influence of relativistic effects on the electronic structure of chromium. The results of calculations demonstrate that the relativistic effects completely change the structure of the Or electron spectrum, which leads to its anisotropy for the directions being identical in the non-relativistic approach. 

As for QgHis, available experimental facts seem to support the above conclusion. Gouterman and Wagniere have indicated that the vibronic analysis of the electronic spectrum weighs against the assumption that bond alternation occurs in CigH,8. Further, the X-ray experiments on CigHig have shown that it has a symmetry... 

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. 

The electronic spectrum reveals at least two states that should be observed, provided the experimental window is enlarged beyond the 2000-6000 A region. 

The acceptor number, AN, of a solvent is a measure of the power of the solvent to accept a pair of electrons [18], Experimental evaluation of AN involves observing the frequency changes induced by a solvent on the 31P NMR spectrum when triethylphosphine oxide, Et3P=0, is dissolved in the solvent. Donation of an electron pair from the oxygen atom of Et3P=0, as shown in Scheme 1.2, reduces the electron density around the phosphorus, causing a deshielding effect which leads to an increase in chemical shift. Hexane (AN = 0) and SbCls (AN = 100) were used as fixed points to define this scale. 

Among them, Li-i-HP can be considered a benchmark model system [29, 30] because its low number of electrons makes possible to calculate accurate PES s. Its electronic spectrum has been meassured by Polanyi and coworkers [22], and has been recently very nicely reproduced using purely adiabatic PES s [31]. In the simulation of the spectrum[31], the transition lines were artificially dressed by lorentzians which widths were fitted to better reproduce the experimental envelop. The physical origin of such widths is the decay of the quasibound states of the excited electronic states through electronic predissociation (EP) towards the ground electronic state. This EP process is the result of the non-adiabatic cou-... 

Until recently, experimental studies of AI were limited to the identification of the process and, in some cases, to the determinations of cross sections or rate constants. It was not possible to draw definite conclusions from this experimental information regarding the involved mechanisms. In recent studies of the AI systems R -H, with R = Ar(3P20), Kr(3P20), Xe(3P2 o), it was verified by electron spectroscopy that the mechanism of Fig. 34b is dominant for these systems.99-101 In all three cases the observed electron spectra extended to the rather high energies of e —1.45 eV (Ar),= 1.0 eV (Kr), and 1.2 eV (Xe) and showed structure resulting from population of different vibrational rotational states as expected for the mechanism of Fig. 34b. As an example, the AI electron spectrum for Ar(3F2.0)-H is shown in Fig. 35. 

Again, since the d orbitals have even parity, even if the molecule does not have an inversion center there is an approximate selection rule in which transitions that would be g -> g (or u -> u) in a parent group with inversion symmetry are allowed. The odd parity vibrations that dominate the single photon spectrum are forbidden, while the even parity vibrations are allowed, but have no advantage over the pure electronic transitions. Experimental two-photon spectra of the sharp-line transitions of Mn4+ in a Cs2Ge F6 host confirm both the simplicity of the spectrum and the relative prominence of the 0-0 lines [55],... 

The decay widths are in meV, citations are given in square brackets. Experimental value for ammonia is lacking because of the vibrational broadening in the Auger electron spectrum of ammonia [65], See Ref. [44] for the details of the Fano-ADC computation. 

R.W. Shaw Jr., J.S. Chen, T.D. Thomas, Auger spectrum of ammonia, J. Elec. Spec. Rel. Phen. 11 (1977) 91 J.M. White, R.R. Rye, J.E. Houston, Experimental Auger electron spectrum of ammonia, Chem. Phys. Lett. 46 (1977) 146 R. CamiUoni, G. Stefani, A. Giardini-Guidoni, The measured Auger electron spectrum of ammonia vapour, Chem. Phys. Lett. 50 (1977) 213. 

Thus 2a2 is experimentally found from the electronic spectrum, ratios of the A s are found from the Raman spectrum, and the Ak s are calculated (except for sign) by pairwise comparison of the Raman intensities. Once the Ak s are calculated, the electronic spectra are calculated by using eq. 2 or 3. 

Fig. 11.9. Experimental setup used for the betatron experiment. Permanent magnets are used simultaneously to deviate the accelerated electron beam off-axis in order to make sure that the X-ray detection is unperturbed and to provide spectral information on the electron energy distribution. CCD pictures of the X-ray beam and the electron spectrum for a gas jet electronic density of 1019 cm-3 are also shown...

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... 

The 7t 7t electronic spectrum predicted by the five-orbital model is in reasonable agreement with experiment, but the inclusion of additional AOs on sulfur does improve the agreement by lowering the Aj and Bj transitions of the second band to fit more closely the experimental value of 6.59 eV. 

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