Electronic and vibrational spectra

The description of states participating in a spin-state transition as electronic isomers with discrete nuclear configurations, in particular different metal-ligand distances, requires that separate electronic and vibrational spectra of the two spin states exist. Indeed, a superposition of the individual vibrational spectra of the two states is in general observed, the relative contribution of the states being a function of temperature [41, 139, 140, 141, 142]. This observation sets a lower limit for the spin-state lifetime longer than the nuclear vibrational period, i.e.,... 

There have been numerous applications of continuum models to equilibria and reactions in solution surveys of these and extensive listings are provided by Cramer and Truhlar.16 Other studies have focused upon the effects of solvents upon solute molecular properties, such as electronic and vibrational spectra,16 dipole moments, nuclear quadrupole and spin-spin coupling constants and circular dichroism.12... 

Several cubic double nitrates of the composition K3M2(N03)9 (M=Pr, Nd, Sm) have been prepared by Carnall et al. (228), to study the electronic and vibrational spectra of the complexes. During this study, they have also investigated the structure of the Pr(IH) analogue and found that each Pr(III) ion is surrounded by twelve oxygens, from six bidentate nitrate groups, in a distorted icosahedral... 

The electronic and vibrational spectra of benzoquinones are very diagnostic. Of the two possible isomers remaining, the 2,5-substituted quinone (5) would be expected to give two different electronic transitions of equal intensity around 280 nm, and only one carbonyl stretching band. The Fourier transform infrared spectrum (CH2CI2) of the haustorial Inducer showed strong absorptions at 1698 (vC=0), 1646 (vC=0) and 1597 cm (vC=C). These spectroscopic data established the haustorial inducer as 2,6-diraethoxy-2"benzoquinone (2,6-DMBQ, 4). 

The physical and spectroscopic properties of a spin-equilibrium complex can appear to be either the average or the superposition of the properties of the separate spin states. Which occurs is dependent on the time scale of the observation relative to the relaxation time of the equilibrium. Thus the electronic and vibrational spectra always appear as a superposition of the two isomers because each spin state possesses a distinctive potential energy surface with its characteristic electronic and vibrational properties. On the other hand, the NMR spectra appear as the average of the spectra of the two spin states, for all but the slowest interconversions, because the frequency of the interconversion is high compared with the frequency differences of the chemical shifts or the inverse of the spin relaxation times of the two isomers. 

NIST also maintains a website called the NIST Chemistry WebBook (http //webbook. nist.gov), which provides access to a broad array of data compiled under the Standard Reference Data Program. This site allows a search for thermochemical data for more than 7000 organic and small inorganic compounds, reaction thermochemistry data for over 8000 reactions, IR spectra for over 16,000 compounds, mass spectra for over 15,000 compounds, UV/VIS spectra for over 1600 compounds, electronic and vibrational spectra for over 5000 compounds, spectroscopic constants of over 600 diatomic molecules, ion energetics data for over 16,000 compounds, and thermophysical properties data for 74 selected fluids. The site allows general searches by formula, name, CAS registry number, author, and stracture and also a few specialized searches by properties like molar mass and vibrational energies. 

Matrix studies see Matrix Isolation) of hydrides have been useful for determining the electronic and vibrational spectra of unstable hydride species, sometimes ones produced by photolysis. For example, HCo(CO)3 has been detected from irradiation of the tetracarbonyl. 

In a recent study of the electronic and vibrational spectra of the /x-amido-decamminedicobalt(III) ion (I), Chester and Brubaker have assigned the spectral bands on the basis of molecular orbital and normal coordinate analysis calculations (34). They concluded that the two halves of the ion (the Co(NH3)5 groups) are electronically independent of each other and assigned the electronic transitions on the basis of a simple tetragonal crystal field with axial compression. The calculations also supported the conclusion that the bonds in the Co-N-Co bridge are very similar to simple C0-NH3 bonds. 

Bazhenov AV, Fursova TN, Kolesnikov NN d al (2007) Electronic and vibrational spectra of a gel of single-wall carbon nanotubes in an ionic liquid. Bull Russ Acad Sd Phys 71 660-662... 

NMR spectroscopy is of special value in differentiating tetracycline antibiotics, since the functionality array common to each member (see (7))so dominates their appearance and physical properties that electronic and vibrational spectra within the group are similar and of little value for identification purposes [79]. Reviews of the H- and C-NMR spectroscopy of tetracycline antibiotics are available [75, 80] these include characteristic features of... 

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