Identification of a mid-infrared electronic absorption band of Fe2+ in the distorted M(2) site of Orthopyroxene, (Mg,Fe)SiO3

An electronic absorption band of Fe²⁺ in the distorted, six-coordinate M(2) site of the common mineral orthopyroxene, (Mg, Fe)SiO₃, is identified at 2350 cm^?1. This band is attributed to the A₁ → B₂ transition within the split ⁵T_2g state of Fe²⁺ in C_2V symmetry.     

Electron microprobe analysis: Optical and electron paramagnetic resonance studies on Mn-rich zoisite (thulite)

The chemical composition of a natural single crystal of manganese-rich zoisite, namely thulite, from Liksiviken, Norway, studied by electron microprobe analysis, was found to contain Mn and Fe as MnO = 0.37 and FeO = 0.196 weight per cent. The results of the optical and electron paramagnetic resonance studies of the sample are reported here. The optical spectrum is mainly due to Mn²⁺ ions and the bands observed at 23,800, 20,915, 20,655, 19,225 and 15,620cm⁻¹ are assigned to the transitions ⁶A₁(S)→⁴T₂(D), ⁶A₁(S)→⁴E(G), ⁶A₁(S)→⁴T₂(G) and ⁶A 1(S)→⁴T₁(G). A low energy band at l3,330 cm⁻¹ is identified as being due to Fe³⁺ ions. Crystal field and Racah parameters evaluated for the Mn²⁺ ion are Dq = 683, B = 683 and C = 2732 cm⁻¹. The presence of Mn²⁺ and Fe³⁺ ions in the crystal is confirmed by EPR spectrum.     

The structure of the dithionite ion

The Raman spectra of aqueous and solid sodium dithionite have been recorded. Differences in the location, intensity, and number of observed bands are attributed to conformational changes in the dithionite ion. The structure of the aqueous ion is non-planar with a C_2h symmetry with an SS bond distance estimated to be 0.220–0.226 nm, as opposed to the dithionite structure in the Na₂S₂O₄·2H₂O salt which is known to have C_2ν structure with a bond distance of 0.2389 nm. The Raman spectra of aqueous dithionite are assigned to A_g (SO) = 997 cm^?1; B_g (SO) at 912 cm^?1, B_g SO₂ twist at 324 cm^?1. The remaining bands are a strong A_g, the SO₂ wag, the SO₂ scissor, and the SS stretch at 584, 461, and 232 cm^?1, respectively, but due to coupling all three motions are expected to exhibit substantial SS character. The variation of the spectra of the solid and aqueous sodium dithionite indicate strong environmental effect on the structure of the anion.     

Equilibrium structure and vibrational frequencies of the O4 molecule

SCF closed shell calculations were performed to determine the equilibrium structure and vibrational frequencies of the O₄ molecule by means of Payne's method and with the help of the molecule's symmetry coordinates. The equilibrium geometry corresponds to symmetry group D_2d with R = 1.505 Å and h = 0.094 Å. The vibrational frequencies are: ν₅(E) = 885.5 cm^?1, ν₃(B₁) = 1051.9 cm^?1, ν₁(A₁) = 1018.3 cm^?1, ν₄(B₂) = 880.3 cm^?1. The second vibrational coordinate (A₁) corresponds to a double-well potential. The first vibrational levels were calculated by a variational method.     

Electronic absorption spectrum of copper formate tetrahydrate

Single crystals of copper formate tetrahydrate were grown at room temperature. Spectra in the near infrared at room temperature and in the visible at room and liquid air temperatures were recorded on a Unicam SP-700 spectrophotometer and Hilger medium quartz spectrograph respectively. The observed absorption bands have been attributed to an ion of Cu²⁺ in tetragonal symmetry with ²B_1g as the ground state. Taking into consideration the spin—orbit coupling associated with the tetragonal field, a successful interpretation of all the observed bands has been made. The band observed in the near infrared at 11000 cm^?1 has been indentified with a vibrational overtone mode of CO₂. The crystal parameters derived are Dq = ?1380 cm^?1, Ds = ?1950 cm^?1, Dt = ?205 cm^?1 and λ = ?830 cm^?1.     

Darstellung,Schwingungsspektren und Normalkoordinatenanalyse von Hexachlororhenat(V) sowie Kristallstruktur von [P(C6H5)4][ReCl6]

Preparation, Vibrational Spectra, and Normal Coordinate Analysis of Hexachlororhenate(V) and Crystal Structure of [P(C₆H₅)₄][ReCl₆] By oxidation of A₂[ReCl₆], A = [(n-C₄H₉)₄N]⁺, [P(C₆H₅)₄]⁺, with Cl₂ in dichloromethane/trifluoracetic acid A[ReCl₆] is formed. [P(C₆H₅)₄][ReCl₆] crystallizes with tetragonal symmetry, space group P4/n-C, a = 12.967(4), c = 7.6992(8) Å, Z = 2. The octahedral complexion [ReCl₆]^? is compressed (C_4v) with the bond lengths, axial Re? Cl1 = 2.28 and Re? Cl3 = 2.24 Å, equatorial Re? Cl2 = 2.31 Å. The infrared active antisymmetric Re? Cl stretching vibration is split into v′₃ = 346 an v″₃ = 326 cm^?1. The assignment of all IR and Raman modes is confirmed by a normal coordinate analysis. The different valence force constants, f_d(ReCl1) = 2.09, f_d(ReCl3) = 2.10, f_d(ReCl2) = 1.88 mdyn/ Å result from the distortion of the octahedron. On excitation with the Ar laser line 514.5 nm a resonance Raman spectrum is observed, showing 8 overtones of v′(A₁) = 382 cm^?1, from which the harmonic frequency ω₁ = 382.1 cm^?1, the anharmonicity constant X₁₁ = ?0.76 cm^?1, and the maximum bond dissociation energy of the [ReCl₆]^? ion to be 138 kcal/mol, are calculated. The vibrational fine structure of the intraconfigurational transitions in the near infrared has been resolved by measuring the absorption spectrum of [(n-C₄H₉)₄N][ReCl₆] at low temperature (10 K), resulting in the assignment of the following electronic origins: Γ₃(³T_1g) → Γ₄(³T_1g): 7 512, Γ₃(³T_1g) → Γ₁(³T_1g): 7 624 and Γ₃(³T_1g) → Γ₅(¹T_2g), Γ₃(¹E_g): 8 368 cm^?1.     

The features of the Cu2+-entry into the structure of tourmaline

EPR and optical absorption spectra of Cu²⁺ ion were investigated in natural elbaites from Brazil and Zambia and in synthetic olenite single crystal. In elbaite from Zambia, the content of Cu²⁺ ions was found to be about 0.006 pfu, whereas in Brazilian elbaite the amount of this ion can approach up to 0.2 pfu. The rose color of elbaite from Zambia is mainly due to optical absorption at 515 nm related to Mn³⁺ ions. The blue color of Brazilian elbaite is related to Cu²⁺ absorption bands at 695 nm and 920 nm. Spin Hamiltonian parameters of Cu²⁺ calculated from the angular dependence of the EPR spectra are: g _x = 2.054, g _y = 2.092, g _z = 2.374; A _x = 27.8·10^?4 cm^?1, A _y = 59.3·10^?4 cm^{? 1}, A _z = 133.2·10^?4 cm^?1. We propose that Cu²⁺ ions enter into Y octahedra with common edges; the symmetry of these Y octahedra is lowered because of local disorder induced by occupancy of the Y site by cations of very different size and charge, such as Li⁺, Al³⁺, and Cu²⁺.     

Ion exchange properties of β-eucryptite (LiAlSiO4): EPR investigation on copper-doped single crystals

Investigation of the ion exchange properties of β-eucryptite (LiAlSiO₄) single crystals indicates that it is impossible to substitute Li⁺ by other bigger univalent cations such as Na⁺, K⁺, or Ag⁺. On the contrary, Li⁺ exchange by bivalent cations, Cu²⁺ or Mn²⁺, is very easy. For a general orientation of the crystal with respect to the magnetic field, the EPR spectrum of Cu²⁺ ions in β-eucryptite consists of 12 sharp lines partially superimposed on a broad line. The sharp lines are attributed to isolated copper ions in the conducting channels. Cu²⁺ lies in sixfold coordinated Li″ sites, but not in the fourfold coordinated Li″ sites. The corresponding spin Hamiltonian parameters at T = 140 K are found to be: g_x = 2.362, g_y = 2.340, g_z = 1.990; ∥A_x∥ = 85 × 10^?4cm^?1, ∥A_y∥ = 71 × 10^?4cm^?1, ∥A_z∥ = 203 × 10^?4 cm^?1. The broad line is attributed to clusters of Cu²⁺ located in neighboring Li″ sites.     

EPR studies of a molybdenyl complex in single crystals of NH4Cl

Electron paramagnetic resonance of [MoOCl₅]^2? has been studied in single crystals of NH₄Cl. At room temperature the interaction of the unpaired electron with both the even and odd isotopes of molybdenum has been observed. The existence of metal-halogen π bonding is established by the observation of the ligand superhyperfine interaction at liquid nitrogen temperatures. Various possible models corresponding to the different spatial configurations of the molybdenyl complex in the lattice are considered to explain the experimentally observed features. The spectra are analysed using the usual spin-hamiltonian corresponding to tetragonal symmetry. The spin-hamiltonian parameters obtained are: g_∥ = 1.964, g_? = 1.945, A_∥ = 75.53 × 10^?4 cm^?1, A_⊥ = 38.42 × 10^?4 cm^?1.     

Paramagnetic resonance of interstitial mo5+ in a tio2 lattice

Paramagnetic absorption of Mo⁵⁺ has been studied in a polycrystalline TiO₂ rutile lattice, The g tensor (g_x = 1.897, g_y = 1.920, g_z = 1.857) and the hyperfine tensor (A_x = 32.7, (A_y = 51.2, (A_z = 58.5 (in 10^?4 cm^?1)) are in agreement with those expected for an nd¹ ion in an interstitial position.     

Parametric analysis of the energy levels of Nd3+ in frozen dilute aqueous solutions of neodymium chloride

A parametric analysis of the Stark-split spectra of Nd³⁺ in frozen dilute aqueous solutions of neodymium chloride has been carried out.The similarity of the spectra of Nd³⁺ in frozen dilute solutions and in crystals, where the ion is nine-fold coordinated and of approximate D_3h symmetry (Nd³⁺: LaCl₃, neodymium ethylsulfate and bromate), was used to obtain initial parameter values. Simultaneous diagonalization of the free ion and crystal field hamiltonians resulted in a r.m.s. deviation σ of 11 cm^?1 for 50 levels. The resulting crystal field parameters are B²₀ = 278 ± 19, B⁴₀ = ?201 ± 39, B^b₀ = ?946 ± 55 and B⁶₆ = 663 ± 43 cm^?1. Selection rules for D_3h are approximately obeyed. The small value of σ, the number of levels accounted for and the fact that the final parameters are not very different from those in the crystals indicate a nine-fold coordination of approximate D_3h symmetry for Nd³⁺ in frozen aqueous solutions. The spectra of liquid solutions show by their similarity to the spectra of frozen solutions that the same surroundings exist in the liquid.     

Elektronisches Resonanz-Raman-Spektrum von Hexabromo-osmat(IV)

Electronic Resonance Raman Spectrum of Hexabromo Osmate(IV) Besides the vibrational bands there are other strong bands in the low-temperature Raman spectrum of [OsBr₆]^2?, which are independent from the excitation line and are interpreted as arising from transitions between the spin-orbit split components of the ³T_1g–Os⁴⁺ ground state. The band at 2800 cm^?1 is anomal polarized and attributable to Γ₁(³T_1g) → Γ₄(³T_1g), while the band at 4880 cm^?1 is depolarized and therefore assigned to Γ₁(³T_1g) → Γ₅(³T_1g). In the electronic Raman spectrum, too, a rigorous resonance-Raman effect is displayed and as far as six overtones of the stretching vibration A_1g and as many combination tones especially with T_2g are observed. Because of the dynamic Jahn-Teller effect Γ₁(³T_1g) → Γ₃(³T_1g) cannot be detected as an electronic Raman transition. Γ₁(³T_1g) → Γ₁(¹T_1g) at 15915 cm^?1 is obtained by luminescence absorption. The results are in good agreement with the absorption spectrum.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

Polyene spectroscopy: Vibronic evidence for a forbidden transition in DECA-2,4,6,8-tetraene

The dimethylpolyene deca-2,4,6,8-tetraene was studied by absorption, fluorescence excitation and fluorescence spectroscopy in glasses at 77 K and in n-alkane crystals at 4.2 K. A strong transition to a ¹B_u excited state is observed with an origin at 32400 cm^?1 in isopentane at 77 K and at 31280 cm^?1 in n-undecane at 4.2 K. A weak transition to a ¹A_g excited state is observed with an origin at 28738 cm^?1 in the n-undecane matrix. The radiative fluorescence lifetime is 500 ns. In undecane the transition from the ground state to the ¹A_g excited state exhibits a classic Herzberg—Teller vibronic pattern indicating a symmetry forbidden transition.     

The photophysics of trans-stilbene

The fluorescence lifetime of trans-stilbene in dilute methylcyclohexane/iso-hexane solution has been measured and the mean S₁ radiative (k_F), radiationless (k_I) and cis-isomerization (k_C) rate parameters have been determined from ?90 to 60°C. S_i consists of a fluorescent trans (¹B_u^*) state (k_F⁰ = 6.0 × 10⁸ s^?1) which undergoes reversible thermal-activated rotational internal conversion (ΔH = 1.75 kcal mole^?1, ΔS = 10.6 cal deg^?1 mole^?1) to a non-fluorescent perp (¹A_g^*) state. p(¹A_g^*) lies 610 cm^?1 above t (¹B_u^*) with an intermediate S₁ potential maximum. p(¹A_g^*) undergoes internal conversion(k_I.^∞ = 5.8 × 10⁸ s^?1) to p (¹A_g) leading to cis-isomerization. This is the main isomerization channel over the whole temperature range.     

Absorption,fluorescence and phosphorescence spectra of the singlet and triplet states of s-tetrazine in the crystal and in mixed crystals at low temperatures

The electronic absorption, fluorescence and phosphorescence spectra of s-tetrazine at low temperatures (4.2-1.5 K) are reported and analyzed in the neat crystal and in several mixed crystals. The ³B_3u-¹A_g (nπ^*) origin is at 18414 ± 5 cm^?1 for neat tetrazine. In the mixed crystal several sites identified. The lowest energy origin is at 17453 cm^?1 for tetrazine in pyrazine; 17 701 cm^?1 in pyrimidine; and 17 676 cm^?1 in pyridazine. The ^eB_3u-¹A_g (nπ^*) origin is at 14 096 ± 2 cm^?1 for the neat crystal. The phosphorescence lifetime of neat tetrazine is measured to be 96.8 ± 2.1 μs at 4.2 and 1.8 K. All the spectra are predominately composed of members of progressions in a single totally symmetric mode (ν_6a) built upon site origins and vibrational fundamentals. The ν_6a interval is: 743 (¹A_g), 715 (³B_3u), and 709 cm^?1 (¹B_3u) in the neat tetrazine crystal; 732 (¹A_g) and 705 cm^?1 (¹B_3u in pyrazine host, 737 (¹A_g) and 701 cm^?1 (¹B_3u) in pyrimidine host, and 732 (¹A_g) and 703 cm^?1 (¹B_3u) in pyridazine host mixed crystals. All emission spectra may be analyzed by Oi → (ν″_6a)^o_n (i), i indicating the observed s     

Vibronic coupling of pyrene in the first ππ* excited state

The two-photon fluorescence excitation spectrum of pyrene in n-hexane and n-heptane matrices has been measured at 10 K in the region of the first electronic transition (26800–30200 cm^?1). The spectrum consists of a rich number of sharp bands, being in general better resolved in n-hexane than in n-heptane matrix. Shpol'skii multiplets have been observed for the most intense bands. A strong two-photon band dominates the spectrum = 1495 cm^?1 from the 0—0 line and was assigned to B_1u × b_1u = A_g symmetry. Other weaker vibronic origins occur in the spectrum which were correlated to vibrational modes of b_1u, b_2u, b_3u and a_u symmetry. Intense vibronic bands are observed close to the origin of the second electronic transition and were interpreted as combination bands of B_1u × b_1u × b_3g symmetry. A two-photon vibronic theory to account for their intensity is proposed where the electronic moment is linearly expanded in powers of the nuclear displacements.     

The molecular structure and conformation of acetamides in the vapour phase: Part III. Thioacetamide (ethanethioamide)

Thioacetamide has been studied by electron diffraction in the gas phase, utilizing a new nozzle construction and using a broad electron beam. The molecule has C_s symmetry, and one C-H bond eclipses the CS bond. The most important structural parameters are: r_g(C-N) = 135.6(3) pm, r_g(C—C) = 151.2(4) pm, r_g(CS) = 164.7(3) pm,∠_αCCS = 122.9(3)° and ∠_αCCN = 114.8(4)°. Parenthesized values are one standard deviation where correlation among data and uncertainty in the electron wavelength have been included. The methyl barrier, V₃, is found from the electron diffraction data to be 4.56 kJ mol^?1. This corresponds to a torsional frequency of 131 cm^?1.     

O‐loss photodissociation of the OCS+ ion in the low‐lying electronic states studied using multiconfiguration second‐order perturbation theory

The CASPT2 potential energy curves (PECs) for O‐loss dissociation from the X²Π, A²Π, B²Σ⁺, C²Σ⁺, 1⁴Σ^?, 1²Σ^?, and 1⁴Π states of the OCS⁺ ion were calculated. The PEC calculations indicate that X²Π, 1⁴Σ^?, 1²Σ^?, and 1⁴Π correlate with CS⁺(X²Σ⁺) + O(³P_g); A²Π and B²Σ⁺ correlate with CS⁺(A²Π) + O(³P_g); and C²Σ⁺ probably correlates with CS⁺(X²Σ⁺) + O(¹D_g). The CASSCF minimum energy crossing point (MECP) calculations were performed for the C²Σ⁺/1⁴Σ^?, C²Σ⁺/1⁴Π, A²Π/1⁴Σ^?, A²Π/1²Σ^?, A²Π/1⁴Π, and B²Σ⁺/1²Σ^? state pairs and the spin‐obit couplings were calculated at the located MECPs. A conical intersection point between the B²Σ⁺ and C²Σ⁺ potential energy surfaces was found at the CASSCF level. Based on our calculations, seven O‐loss predissociation processes of the C²Σ⁺ state are suggested and an appearance potential value of 7.13 eV for the CS⁺ + O product group is predicted. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011