Visible region absorption and excitation spectroscopy of K2ReCl6 and various ReCl2−6 containing A2MCl6 host crystals

For pure K₂ReCl₆ and ReCl²⁻₆ in K₂SnCl₆, K₂PtCl₆ and (NR₄)₂SnCl₆ (R = H, Et, Me, Pr) several new transitions located from 16000 to 20000 cm⁻¹ were found using absorption and excitation spectroscopy which cannot be assigned to intraconfigurational transitions of ReCl²⁻₆. These may be due to either impurity or site interaction effects or interconfigurational transitions. Everything possible has been done to rule out the former possibility and the host dependences are not consistent with site effects. If the latter source is correct, the appearance of these transitions indicates large deviations from the ligand field model in this sytem. In particular, exceptionally low values for the Dq parameter are required to fit the calculated ligand field energy levels to any interconfigurational assignment of the new transitions. This could be evidence of strong mixing of d-d and charge transfer states not represented in the ligand field model.     

Intraconfigurational absorption spectroscopy of IrCl2−6 and IrBr2−6 in A2MX6-type host crystals

Near-IR absorption spectra for Ir⁴⁺ in A₂MX₆ (A  K, Rb, NH₄, M  Sn, Pt, Re, X  Cl, Br)-type hosts are discussed and compared to earlier work. Our data indicate that the effect of reduced host symmetry is quite small in this d⁵ system and that the IrCl²⁻₆ spectra can be interpreted in a manner paralleling previous studies on Ir⁴⁺ in cubic hosts. In some hosts, e.g., K₂PtCl₆, the IrBr²⁻₆ appears to have a vibronic pattern outside the experience with previous MX²⁻₆ results. Origin shifts and the nature of a vibronic progression were seen to correlate with host lattice counterion. By comparison to luminescence results of Flint and Paulusz, the latter data are proposed to be indicative of a strongly Jahn-Teller active e_g mode.     

Temperature-dependent luminescence spectra of [ReCl6]2− doped in K2PtCl6-type crystals

Luminescence spectra of [ReCl₆]²⁻ doped in various cubic Rb₂MCl₆ (M = Te, Sn) host crystals have been measured at temperatures between 20 and 240 K. Excitation was obtained at different energy using various laser lines. The intensities of vibronic fundamentals belonging to the Γ₇(²T_2g) → Γ₈(⁴A_2g) transition are compared to theoretical models which describe temperature-dependent transition rates giving rise to vibronic sidebands.     

Anomalous temperature dependence of the OH− absorption band in stoichiometric LiNbO3 crystals

Infrared absorption spectra of the stretching vibration of OH⁻ and OD⁻ ions in stoichiometric LiNbO₃ crystal have been measured in the temperature range 10–310 K. The band parameters, halfwidth and position, have been determined with high accuracy by assuming quasi-Voigt line shapes. Anomalous behaviour of the OH⁻ band position has been observed and interpreted by phonons coupled to the stretching vibration with coupling constants of alternate signs.     

High-resolution Fourier transform infrared absorption spectroscopy of the ν6 band of c-C3H2

The gas-phase high-resolution absorption spectrum of the ν(6) band of cyclopropenylidene (c-C(3)H(2)) has been observed using a Fourier transform infrared spectrometer for the first time. The molecule has been produced by microwave discharge in an allene (3.3 Pa) and Ar (4.0 Pa) mixture inside a side arm glass tube. The observed spectrum shows a pattern of c-type ro-vibrational transitions in which the Q-branch lines strongly and distinctly stand out in the spectrum. A combined least-squares analysis of the observed 216 ro-vibrational transitions together with 28 millimeter-wave rotational transitions from the previous study has resulted in an accurate determination of the molecular constants in the ν(6) state. The band center is found to be at 776.11622(13) cm(-1) with one standard deviation in parentheses, which is 2.3% lower than the matrix isolation value. The intensity ratio I(3)(ν(3))/I(6)(ν(6)) obtained from the observed ν(3) and ν(6) bands, 1.90(9), is somewhat lower than the ratio estimated from ab initio (2.4-2.6) and DFT (2.8) calculations.     

Photochemical production of F centers in KBr crystals doped with Se2−

The photochemical production of F centers in KBr.Se²⁻ crystals has been investigated using crystals doped by a method different to that used by others. The formation of F centers is a complicated process and depends on the intensity of irradiating light, temperature and wavelength. Low-power irradiation favors F center formation by ionization of free Se²⁻ in freshly quenched crystals. Low-temperature UV laser irradiation forms both normal F centers and one other center with an absorption band very close to the normal F center. The nature of this second center is not known.     

A study of peralkylated derivatives of bis(η6-benzene)chromium by gas-phase electronic absorption spectroscopy

The gas-phase electronic absorption spectra of (⁶-C₆R₆)₂Cr (R = Me (1) and Et (2)) reveal Rydberg structures, which disappear on going to the condensed phase. Each spectrum shows a Rydberg series converging to the ionization threshold. The first ionization potential determined as the series convergence limit is 4.662±0.008 eV for 1 and 4.667±0.019 eV for 2. The Rydberg bands are due to the transitions from the non-bonding MO 3d_z2 to the R4s and Rnp (n = 4—10) levels. The influence of methyl and ethyl substituents on the term values of the Rydberg transitions depends on the principal quantum number of the Rydberg MO.     

A Mössbauer spectroscopy investigation of SrFe1−xScxO3−δ perovskites

Polycrystalline samples of oxygen deficient perovskites SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5) have been synthesized by direct solid state reactions. Each compound has been stabilized with two different oxygen stoichiometries. The structural study shows, firstly, the good cationic homogeneity of the samples and, secondly, that the Sc and Fe atoms are randomly distributed over the same crystallographic site, whatever the scandium content. This implies that no anionic order is possible. A detailed Mossbauer spectroscopy study clearly shows that the substitution of scandium for iron involves an oxygen content decrease which decreases the tetravalent iron content until its total disappearance for x = 0.5. The evolutions of the isomer shift, the quadrupolar splitting and the relative intensity versus the Sc³⁺ content are depicted in the present paper.     

Negative ion photoelectron spectroscopy of teo−

We have recorded the photoelectron spectrum of Te0⁻ using a hot-cathode discharge ion source and a negative ion photoelectron spectrometer. The adiabatic electron affinity of TeO is determined to be 1.697±0.022 eV. The negative ion parameters determined in this work are: (w_e″(TeO⁻) = 690 ± 80 cm⁻¹, r_e″(TeO⁻) = 1.884 ± 0.028 Å. and D_o     

The quantitative determination of the S0—T1 absorption in pyrene with the use of intracavity absorption spectroscopy

The spin-forbidden S₀—T₁ transition of pyrene was quantitatively investigated by applying intracavity absorption spectroscopy. The measurements were carried out in benzolic solutions. The molar decadic extinction coefficient of the 0—0 transition was determined to 6.0 × 10⁻⁴ dm³mol⁻¹ cm⁻¹. The integral absorptivity was calculated to 2.94 × 10⁻² dm³ mol⁻¹ cm⁻¹ and yielded an intrinsic phosphorescence lifetime of 55.4 s. The intracavity absorptions were measured in a cavity-dumped Rhodamine 6G dye laser. Absorbances were recorded in the range between 8 × 10⁻⁴ and 5 × 10⁻⁶.     

The electronic structure of Bi2−xGdxRu2O7 and RuO2: A study by electron spectroscopy

The bismuth gadolinium pyrochlore ruthenates Bi_2−xGd_xRu₂O₇ have been studied in relation to RuO₂ by the techniques of X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and high-resolution electron-energy-loss spectroscopy (HREELS). The composition-dependent metal-to-semiconductor transition in the pyrochlore system is mirrored by the progressive decrease with composition parameter in (i) the density of electronic states at the Fermi energy in UPS, (ii) the plasmon frequency in HREELS, and (iii) the probability of screening a Ru : 3d core hole in XPS. These changes are too gradual in themselves to pinpoint the transition, but are generally consistent with transport and X-ray diffraction data that indicate a metal-to-nonmetal transition at x = 1.55 mediated by an interplay between disorder and correlation-induced electron localization. Comparison of the results for the pyrochlores with those from RuO₂ suggest that the fine structure in the Ru : 3d spectrum of the latter material, previously believed to arise from differing oxidation states at the surface, should in fact be attributed to final-state screening effects in a stoichiometric material. Our conclusion is confirmed by the signals associated with Ru : 4d electrons in XPS, UPS, and HREELS: each of these three techniques appears to probe a conduction-electron concentration essentially equal to its bulk value. In particular, UPS confirms details of the band structure of RuO₂ not obvious from previous photoemission experiments.     

Dielectric relaxation and ultrafast transient absorption spectroscopy of [C6mim]+[Tf2N]−/acetonitrile mixtures

Mixtures of the ionic liquid (IL) [C(6)mim](+)[Tf(2)N](-) and acetonitrile have been investigated by a combination of dielectric relaxation spectroscopy (DRS) and ultrafast transient absorption techniques using the molecular probe 12'-apo-β-carotenoic-12'-acid (12'CA). Steady-state absorption spectra of the 12'CA molecule have also been recorded. The position of the probe's S(0)→ S(2) absorption maximum correlates linearly with the polarizability of the mixture, suggesting that the bulk composition is a good approximation to the local composition. The lifetime τ(1) of the S(1)/ICT state of 12'CA varies rather smoothly with composition between the value for pure acetonitrile (42 ps) and neat [C(6)mim](+)[Tf(2)N](-) (94 ps). At low IL contents there appears to be an influence of discrete ion pairs. Employing static dielectric constants from the DRS experiments, one finds that the lifetime of the probe in the IL mixtures is shorter than that in pure organic solvents with the same polarity parameter. This suggests an increased stabilization of the S(1)/ICT state in IL-containing mixtures, most likely due to IL-specific Coulombic interactions between the cation and the negative end of the probe's dipole. An ultrafast solvation component is observed which is ca. 0.5 ps in pure acetonitrile, and approaches the value for the pure IL (2.0 ps) already around x(IL) = 0.3. This is interpreted in terms of an efficient perturbation of the cooperative solvation response of acetonitrile by the presence of small amounts of IL and possibly also the viscosity increase when adding IL. This view is also supported by the increase of the average longitudinal relaxation time of acetonitrile upon addition of small IL amounts extracted from the DRS experiments.     

Davydov splitting in the polarized absorption spectra of single crystals of some copper complexes of α-amino acids

This paper presents the absorption spectra observed with polarized light of the single crystals of the copper complexes of L-alanine and DL--aminobutyric acid.The spectra are interpreted by the crystal-field theory.

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Zusammenfassung Es werden die Absorptionsspektren angegeben, welche mit Hilfe polarisierten Lichts an Einkristallen der Kupferkomplexe von L-Alanin und DL--AminobuttersÄure beobachtet wurden.Die Spektren wurden an Hand der Kristallfeldtheorie gedeutet.

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Résumé On donne les spectres d'absorption observés, à l'aide de lumière polarisée, aux cristaux uniques des complexes de cuivre du L-alanine et de l'acide DL--aminobutyrique.Les spectres sont interprétés suivant la théorie du champ cristallin.

     

Investigation of hydration of α-amino acids by means of absorption millimeter spectroscopy

The hydration indexes for 19 protein -amino acids are measured by means of absorption millimeter spectroscopy (AMS) at 31.42 GHz. The plot of the hydration indexes on the area of surface of aliphatic amino acid molecules accessible for water is a straight line located above the points corresponding to aromatic or polar amino acids. The contribution of nonpolar groups in the hydration index is greater than that of polar groups provided that their accessible surface areas are equal. The contribution to hydration of -OH and-CONH₂ groups in Ser. Gin, and Asn coincides in sign with that of pure hydrophobic hydration but the value of the contribution is significantly smaller. The change in mobility of water molecules, which is the basis of the AMS method, may serve as the physicochemical foundation for the construction of a new hydrophobicity scale for amino acids comparable with the already existing scales.Deceased September 2, 1995.Translated fromIzvestiya Akodemii Nauk. Seriya Khimicheskaya, No. 3, pp. 618–622, March, 1996.     

The oriented C2Cl6− radical in irradiated hexachloroethane single crystals: An EPR and molecular-orbital study

The C₂Cl₆⁻ radical has been detected by EPR methods in X-ray irradiated C₂Cl₆ crystals at 77 K. The radical, which decays rapidly upon exposure to visible light at 77 K, retains the staggered configuration of C₂Cl₆ and exhibits a structure in which the directions of the largest chlorine hyperfine tensor component and smallest component of the g-tensor occur close to the CC bond direction. In contrast, an INDO calculation predicts that the largest unpaired electron density occurs along the CCl bond direction and the CCl bond length increases by 0.4 Å upon electron addition.     

Negative ion photoelectron spectroscopy of N2O− and (N2O)−2

We have recorded the photoelectron spectra of the gas phase negative ions N₂O⁻ and (N₂O)₂⁻ both of which were prepared in a nozzle ion source. The shift between the maxima of the two spectra is interpreted in terms of the dissociation energy of the dimer ion.     

Ferrimagnetic spinels in hydrothermal and thermal treatment of MnxFe2−2x(OH)6−4x

Products of hydrothermal treatment of the initial amorphous system Mn_xFe_2–2x(OH)_6–4x for 0x1 in 0.1x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supported by magnetic measurements. After hydrothermal growth for lowx, hematite and goethite phases occurred. Although the goethite phase was still identifiable atx=0.6, formation of a solid solution with the isostructural groutite was not found. The ferrimagnetic spinel phase, which resists heating up to 400C, was present at 0.5x0.9. At higher temperatures, it transformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. AtT900C, a ferrimagnetic spinel structure reappeared up tox=0.8. For x=0.9, the low- and high-temperature forms of the hausmannite phase occurred, forx= 1 passing from one form into another through Mn₅O₈ and partritgeite.For a primary mixture Mn_0.5Fe(OH)₄, corresponding to the manganese ferrite structure, the lattice parameter of which passes from 8.43 å through 8.33 å to 8.50 å, the probable crystallochemical formula was suggested.We are grateful to KBN (The State Committee for Scientific Research, Poland) for grant No. 3 T09A 064 08, which contributed substantially to the materialization of this project.     

Anion⋅⋅⋅Anion Attraction in Complexes of MCl3− (M=Zn,Cd, Hg) with CN−

High-level ab initio calculations show that the MCl₃⁻ anions comprising Group 2B M atoms Zn, Cd, and Hg form a stable complex with the CN⁻ anion, despite the like charge of the two ions. The complexation occurs despite a negative π-hole region above the M atom of MCl₃⁻. The dimerization distorts the planar geometry of MCl₃⁻ into a pyramidal shape which reduces the negative potential above the M atom, facilitating a close approach of the two anions, with R(M⋅⋅⋅C)∼2 Å, and an overall attractive electrostatic attraction within the dimer. In the gas phase, this dimer is less stable than the pair of separated ions by some 30 kcal/mol. However, the dissociation must surmount an energy barrier of roughly 25 kcal/mol which occurs at an intermolecular distance of 4 Å. In aqueous solution, the dimerization process is exothermic and barrier-free, with a binding energy in the 11–18 kcal/mol range.     

A quantum chemical study of the infrared absorption intensities of the isoelectronic C2v systems H2F+, H2O and NH−2

The results of a comparative theoretical study of the dipole moment derivatives and infrared absorption intensities within the double harmonic approximation are presented for the isoelectronic, isostructural C_2v molecules: H₂F⁺, H₂O and NH⁻₂. The calculations, performed at the ab initio SCF and CI levels of theory, utilize basis sets of triple zeta+two polarization functions quality. For the ions H₂F⁺ and NH⁻₂, in the absence of adequate experimental data the equilibrium geometries and force constants were also calculated. The trends observed in the dipole moment derivatives for the three systems are indicative of the amount of electronic charge associated with the hydrogen atoms and are very similar to the trends noted for a set of C_3v hydrides.