Polarized Electronic Absorption Spectra Research Articles

Polarized electronic absorption spectra of colourless chalcocyanite, CuSO4, with a survey on crystal fields in Cu2+ minerals

Polarized electronic absorption spectra of colourless chalcocyanite, CuSO4, have been measured using microscope-spectrometric techniques. The spectra are characterized by a structured and clearly polarized band system in the near-infrared spectral range with components centred at 11,720, 10,545, 9,100, and 7,320 cm−1, which have been assigned to crystal field d–d transitions of Cu2+ cations in pseudo-tetragonally elongated CuO6 polyhedra with point symmetry Ci (\(\bar{1}\)). The polarization behaviour is interpreted based on a D2(C2″) pseudo-symmetry. Crystal field calculations were performed for the actual triclinic point symmetry by applying the Superposition Model of crystal fields, as well as in terms of a ‘classic’ pseudo-tetragonal crystal field approach yielding the parameters Dq(eq) = 910, Dt = 395, and Ds = 1,336 cm−1, corresponding to a cubically averaged Dqcub = 679 cm−1. A comparative survey on crystal fields in Cu2+ minerals shows that the low overall crystal field strength in chalcocyanite, combined with a comparatively weak pseudo-tetragonal splitting of energy levels, is responsible for its unique colourless appearance among oxygen-based Cu2+ minerals. The weak crystal field in CuSO4 can be related to the lower position of the SO42− anion compared to, e.g. the H2O molecule in the spectrochemical series of ligands.

Crystal structure, electronic absorption spectra, and crystal field superposition model analysis of Li2Co3(SeO3)4

Abstract Single crystals of the new compound Li2Co3(SeO3)4 have been synthesized under low-hydrothermal conditions. The structure was determined by direct methods from single crystal X-ray diffraction data (monoclinic, space group P21/c, a = 8.095(2) Å, b = 9.236(3) Å, c = 7.781(2) Å, β = 115.76(1)°, V = 523.9 Å3, Z = 2; R1 = 0.034 for 1613 F o > 4σ(F o) and 98 variables). Li2Co3(SeO3)4 builds a framework structure composed of one type of [4 + 2] coordinated Li atoms and each two crystallographically different CoO6 octahedra and pyramidal SeO3 groups. The polyhedra of lithium and of one type of the cobalt atoms exhibit uncommonly strong irregular distortions. Polarized electronic absorption spectra of Li2CO3(SeO3)4 from 35000 to 4000 cm−1 were obtained by microscope-spectrometric techniques. The spectra were evaluated in terms of crystal field superposition model calculations for both triclinic Co2+ sites giving the first complete set of superposition model parameters for Co2+, i.e. the intrinsic parameters [unk]2 = 7000 cm−1 and [unk]4 = 4740 cm−1, and the power-law exponents t 2 = 5.5 and t 4 = 3.1. The interelectronic repulsion parameters are Racah B = 805 cm−1 and Racah C = 3630 cm−1. As already observed for several other selenite compounds, the derived crystal field strength parameters Dq cub again indicate a rather low position of the [SeO3]2− anion within the range of oxygen-based ligands in the spectrochemical series.

Polarized electronic absorption spectra of Cr 2 SiO 4 single crystals

Polarized electronic absorption spectra, E∥a(∥X), E∥b(∥Y) and E∥c(∥Z), in the energy range 3000–5000 cm–1 were obtained for the orthorhombic thenardite-type phase Cr2SiO4, unique in its Cr2+-allocation suggesting some metal-metal bonding in Cr2+Cr2+ pairs with Cr-Cr distance 2.75 A along [001]. The spectra were scanned at 273 and 120 K on single crystal platelets ∥(100), containing optical Y and Z, and ∥(010), containing optical X and Z, with thicknesses 12.3 and 15.6 μm, respectively. Microscope-spectrometric techniques with a spatial resolution of 20 μm and 1 nm spectral resolution were used. The orientations were obtained by means of X-ray precession photographs. The xenomorphic, strongly pleochroic crystal fragments (X deeply greenish-blue, Y faint blue almost colourless, Z deeply purple almost opaque) were extracted from polycrystalline Cr2SiO4, synthesized at 35 kbar, above 1440 °C from high purity Cr2O3, Cr (10% excess) and SiO2 in chromium capsules. The Cr2SiO4-phase was identified by X-ray diffraction (XRD). Four strongly polarized bands, at about 13500 (I), 15700 (II), 18700 (III) and 19700 (IV) cm–1, in the absorption spectra of Cr2SiO4 single crystals show properties (temperature behaviour of linear and integral absorption coefficients, polarization behaviour, molar absorptivities) which are compatible with an assignment to localized spin-allowed transitions of Cr2+ in a distorted square planar coordination of point symmetry C2. The crystal field parameter of Cr2+ is estimated to be 10 Dq≃10700 cm–1. A relatively intense, sharp band at 18400 cm–1 and three other minor features can, from their small half widths, be assigned to spin-forbidden dd-transitions of Cr2+. The intensity of such bands strongly decreases on decreasing temperature. The large half widths, near 5000 cm–1 of band III are indicative of some Cr-Cr interactions, i.e. δ-δ* transitions of Cr24+, whereas the latter alone would be in conflict with the strong polarization of bands I and II parallel [100]. Therefore, it is concluded that the spectra obtained can best be interpreted assuming both dd-transitions of localized d-electrons at Cr2+ as well as δ-δ* transitions of Cr24+ pairs with metal-metal interaction. To explain this, a dynamic exchange process 2 Crloc2+⇔Cr2, cpl4+ is suggested wherein the half life times of the ground states of both exchanging species are significantly longer than those of the respective optically excited states, such that the spectra show both dd- and δ-δ*-transitions.

Polarized electronic absorption spectra of 3d3-configurated tetravalent manganese in octahedral fields of Mn(SeO3)2

Polarized optical absorption spectra of Mn(IV) in octahedral crystal fields of Mn(SeO3)2 have been studied by means of microscope-spectrometry in the range 40000-4000 cm−1 and at temperatures between 113 K and 293 K. Intense charge-transfer absorptions (linear absorption coefficient α ≫ 30000 cm−1) completely mask the d-d transitions in the UV and VIS region above ≈23000 cm−1. The optical electronegativity χopt of Mn(IV) in Mn(SeO3)2 is estimated to be 2.7. In accordance with the d3 configuration of tetravalent manganese three d-d bands observed at ambient temperatures at 13250, 14137 (α≈50 cm−1) and ≈18500 cm−1 (α≈500–800 cm−1) are assigned to the spin forbidden 4A2g→2Eg and 4A2g→2T1g transitions as well as to the first spin allowed 4A2g→4T2g transition, respectively. These assignments allow the calculation of the following ligand field parameters: Dq ≈ 1850 cm−1, B55 = 869 cm−1 (β55 = 0.82), and C = 2346 cm−1 (293 K).

Polarized electronic absorption spectra and Ni-Mg partitioning in olivines (Mg1-xNix)2[SiO4

Polarized electronic absorption spectra and Ni-Mg partitioning in olivines (Mg1-xNix)2[SiO4

Luminescence and absorption spectra ofM2UO2Cl4·xH2O

Polarized luminescence and electronic absorption spectra have been recorded at temperatures down to 4 K for M 2UO2Cl4·xH2O (M=K, Rb, NH4). The most important difference between these luminescence spectra and that of Cs2UO2Cl4 arises from the contribution of vibrations of water molecules to the vibronic intensity. In the electronic absorption spectra the wavenumbers of these vibrations may be used to locate and identify electronic origins. Ten electronic origins have been identified at similar wavenumbers to those reported by Denning et al. for Cs2UO2Cl4. New ground state vibrational assignments for M 2UO2Cl4·xH2O are made from 85 K infrared and 120 K Raman data.

Polarized electronic absorption spectra for dimolybdenum(II) tetraacetate

Polarized spectra with rich vibrational detail are reported for two faces of single crystals of Mo/sub 2/(O/sub 2/CCH/sub 3/)/sub 4/ at temperatures down to 5 K. Evidence, which includes the orientation in space of transition moments for individual vibrational lines, hot bands, and Franck-Condon factors, is presented that the 23,000-cm/sup -1/ band is the electric-dipole-allowed /sup 1/A/sub 2u/ reverse arrow /sup 1/A/sub 1g/ or delta* reverse arrow delta with an origin at 21,700 cm/sup -1/. However, the intensities are sufficiently low that lines excited vibronically, although somewhat weaker, approach the intensity of the dipole-allowed progression. A second transition at 26,500 cm/sup -1/ is evident as well from the low-temperature spectra. The spectra of a number of dimeric carboxylate complexes of molybdenum(II) are compared and the possible cause of the exceptionally low intensity for an electric-dipole-allowed transition is discussed.

Polarized electronic absorption spectra for dirhodium(II) tetraacetate dihydrate

Single-crystal polarized absorption spectra are reported for the 1-bar 01 face of Rh/sub 2/(O/sub 2/CCH/sub 3/)/sub 4/2H/sub 2/O in the region of 15,500-30,000 cm/sup -1/ and at temperatures of 300 and 15 K. an absorption band with a maximum at 17,300 cm/sup -1/ possesses vibrational structure in the perpendicular to b polarization. It corresponds to molecular x,y polarization and has been assigned as Rh-Rh ..pi..*..-->..Rh-Rh sigma*. Weaker absorptions with maxima at 23,300 cm/sup -1/ in perpendicular to b and 22,200 cm/sup -1/ in double vertical bars b indicate the presence of more than one transition in this region. Possible assignments for these transitions are discussed. 3 figures.

Polarized electronic absorption spectra of crystalline charge transfer autocomplexes

The polarized visible absorption spectrum of oriented polycrystalline intramolecular charge transfer autocomplexes were observed for ten molecular compounds of the 1,4-naphthoquinone series. Two wide bands appear if the electric vector of the incident light wave is oriented parallel to the long axis of the crystal. These bands are assigned to intermolecular charge transfer interaction and it is suggested that the existence of two bands is due to alternation in donor-acceptor distances in the crystal. Orientation of transition moments for inter- and intramolecular interaction has also been estimated.

Polarized electronic absorption spectra for potassium tetrabromoplatinate(II) dihydrate. Spectral effects of a platinum(IV) component

Crystals of the metastable compound K/sub 2/PtBr/sub 4/.2H/sub 2/O have an orthorhombic structure, space group Pbam, with a:b:c = 8.31 (2):13.73 (3):4:84 (1) A and Z = 2. The PtBr/sub 4//sup 2 -/ ions occupies a crytallographic site of C/sub 2h/ symmetry but retains essentially a D/sub 4h/ molecular symmetry with the z axis directed along c. The absorption spectra in the d reverse arrow d region were recorded for a, b, and c polarizations. Band maxima lie at 300 to 800 cm/sup -1/ higher energies than in anhydrous K/sub 2/PtBr/sub 4/. The /sup 1/A/sub 2g/ reverse arrow /sup 1/A/sub 1g/ transition, forbidden in z polarization, was not observed in polarization. Vibrational components were resolved in the /sup 3/B/sub 1g/ shoulder and in the /sup 1/A/sub 2g/ peak. Striking differences in intensities which occurred in the a and b polarization indicated that crystal effects were important in the vibronic excitation process. Red sections, in some crystals, were attributed to a dipole-allowed band, completely c polarized, for a mixed-valence electron-transfer transition involving a PtBr/sub 6//sup 2 -/ impurity defect. 6 figures, 3 tables.

ChemInform Abstract: ELECTRONIC STRUCTURE OF SULFUR COMPOUNDS. 22. THE ELECTRONIC STRUCTURE OF 1,3‐DITHIOLE‐2‐THIONE AND ITS SELENIUM ANALOGS. PHOTOELECTRON SPECTRA AND POLARIZED ELECTRONIC ABSORPTION SPECTRA

Chemischer InformationsdienstVolume 8, Issue 29 Physical Organic Chemistry ChemInform Abstract: ELECTRONIC STRUCTURE OF SULFUR COMPOUNDS. 22. THE ELECTRONIC STRUCTURE OF 1,3-DITHIOLE-2-THIONE AND ITS SELENIUM ANALOGS. PHOTOELECTRON SPECTRA AND POLARIZED ELECTRONIC ABSORPTION SPECTRA J. SPANGET-LARSEN, J. SPANGET-LARSENSearch for more papers by this authorR. GLEITER, R. GLEITERSearch for more papers by this authorM. KOBAYASHI, M. KOBAYASHISearch for more papers by this authorE. M. ENGLER, E. M. ENGLERSearch for more papers by this authorP. SHU, P. SHUSearch for more papers by this authorD. O. COWAN, D. O. COWANSearch for more papers by this author J. SPANGET-LARSEN, J. SPANGET-LARSENSearch for more papers by this authorR. GLEITER, R. GLEITERSearch for more papers by this authorM. KOBAYASHI, M. KOBAYASHISearch for more papers by this authorE. M. ENGLER, E. M. ENGLERSearch for more papers by this authorP. SHU, P. SHUSearch for more papers by this authorD. O. COWAN, D. O. COWANSearch for more papers by this author First published: July 19, 1977 https://doi.org/10.1002/chin.197729039AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue29July 19, 1977 RelatedInformation

Polarized electronic absorption spectra of (n-Bu4N)2[Pt(CN)4] at 5 K

Polarized electronic absorption spectra of (n-Bu4N)2[Pt(CN)4] at 5 K