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.     

Temperature dependence of the bandwidths and frequencies of some anthracene phonons. High-resolution Raman measurements

Using a coupled interferometer—spectrometer with a resolution of 0.02 cm^?1 we have measured the Raman band profiles of the four low-frequency anthracene phonons ω₁(a_g), ω₂(a_g), ω₆(b_g) and ω₇(b_g) in the temperature range 2–70 K. These phonons possess very narrow bandwidth at low temperature which are convinently measured under high resolution. In particular the two lowest-frequency phonons ω₁(a_g) and ω₆(b_g) have a bandwidth at 2 K of 0.045 cm^?1. The other two phonons ω₇(b_g) and ω₂(a_g) have bandwidths at 2 K of 0.165 and 0.4 cm^?1, respectively. A detailed analysis of the bandwidth variation with temperature was made in terms of three-phonon decay processes. The exrerimental variation of the bandwidth with temperature was correctly reproduced assuming a single down-and up-process. The following results were obtained: ω₁(a_g): 49.45 cm^?1 = 2×24.72 cm^?1, 49.45 cm^?1 = 98.45 cm^?1 ?49.0 cm^?1; ω₆(b_g): 57.50 cm^?1 = 2×28.75 cm^?1, 57.50 cm^?1 = 108.50 cm^?1 ?51.0 cm^?1; ω₇(b_g): 71.20 cm^?1 = 2×35.6 cm^?1, 71.20 cm^?1 = 120.20 cm^?1 ?49.0 cm^?1: ω₂(a_g): 82.40 cm^?1 = 57.50 cm^?1 +24.9 cm^?1, 82.40 cm^?1 = 138.4 cm^?1 ?56 cm^?1. The efficiency of the down- and up-processes is discussed in terms of the two-phonon density of states. The bandwidths at 2 K follows very closely the variation of the two-phonon sum density of states, whereas the relative importance of the up-processes follows well the two-phonon difference density of states. The anharmonic frequency shifts are corrected for the thermal expansion of the crystal using the Grüneisen single-phonon parameters and the thermal expansion coefficients given in the literature. This permits an estimation of the variation of the anharmonic shifts in the temperature range studied.     

Infrared absorption and magnetic circular dichroism of Cs2ZrCl6:Ir4+

The E″_g(²T_2g) å U′_g(²T_2g) transition of Ir⁴⁺ in Cs₂ZrCl₆ is observed in the infrared energy range 5000–6000 cm^?1 by absorption and magnetic circular dichroism spectroscopy. The resolved vibrational structure provides detailed information about the change in vibrational frequencies on excitation and the transition intensity mechanism. The energy of the transition requires the Ir⁴⁺ spin-orbit coupling parameter ζ to be ≈ 2800 cm^?1.     

Interpretation of the light scattering spectrum of paramagnetic FeF2

The Raman spectrum of a single crystal of FeF₂ is reported and the transitions in the range of 900–1500 cm^?1 are assigned to the spin-orbit levels of the Fe²⁺ ion in a field of D_2h symmetry. The value of the tetragonal and rhombic distortion parameters calculated from the spectra are ?1162 cm^?1 and 110 cm^?1, respectively and the spin-orbit coupling parameter λ = ?91.3 cm^?1. The computed energy level diagram is in agreement with the EPR spectrum of this compound.     

Darstellung,Eigenschaften und elektronische Raman-Spektren von Bis(chloro)phthalocyaninatoferrat(III), -ruthenat(III) und -osmat(III)

Preparation, Properties and Electronic Raman Spectra of Bis(chloro)-phthalocyaninatoferrate(III), -ruthenate(III) and -osmate(III) Bis(chloro)phthalocyaninatometalates of Fe^III, Ru^III and Os^III [MCl₂Pc(2-)]^?, with an electronic low spin ground state are formed by the reaction of [FeClPc(2-)] resp. H[MX₂Pc(2?)] (M = Ru, Os; X = Cl, I) with excess chloride in weakly coordinating solvents (DMF, THF) and are isolated as (n-Bu₄N) salts. The asym. M? Cl stretch (ν_as(MCl)) is observed in the f.i.r. at 288 cm^?1 (Fe), 295 cm^?1 (Ru), 298 cm^?1 (Os), ν_as(MN) at 330 cm^?1 (Fe), 327 cm^?1 (Ru), and 317 cm^?1 (Os); only ν_s(OsCl) at 311 cm^?1 is resonance Raman (r.r.) enhanced with blue excitation. The m.i.r. and FT-Raman spectra are typical for hexacoordinated phthalocyanines of tervalent metal ions. The UV-vis spectra show besides the characteristic π-π* transitions (B, Q, N, L band) of the Pc ligand a number of extra bands at 12–15 kK and 18–24 kK due to trip-doublet and (Pc→M)CT transitions. The effect of metal substitution is discussed. The r.r. spectra obtained by excitation between the B and Q band (λ₀ = 476.5 nm) are dominated by the intraconfigurational transition Γ₇ Γ ₈ arrising from the spin-orbit splitting of the electronic ground state for Fe^III at 536 cm^?1, for Ru^III at 961 cm^?1 and Os^III at 3 028 cm^?1. Thus the spin-orbit coupling constant increases very greatly down the iron group: Fe^III (357 cm^?1)< Ru^III (641 cm^?1)< Os^III (2 019 cm^?1). The Γ₇ Γ ₈-transition is followed by a very pronounced vibrational finestructure being composed in the r.r. spectra by the coupling with ν_s(MCl), δ(MClN) and the most intense fundamental vibrations of the Pc ligand. In absorption only vibronically induced transitions are observed for the Ru and Os complex at 1 700-2800 rsp. 3100-5800 em^?1 instead of the 0-0 phonon transitions. The most intense lines are attributed to combinations of the intense odd vibrational mo-des at ≈ 740 and 1120 cm^?1 with ν₅(MCI), δ(MClN).     

RESONANCE RAMAN SPECTRUM OF THE EXCITED 21Ag STATE OF ß-CAROTENE

Abstract— Resonance Raman (RR) bands assignable to the 2¹A_g excited state of ß-carotene are recorded using picosecond time-resolved resonance Raman (PTR³) spectroscopy. The RR spectrum contains bands in both the C-C (1204 cm^?1, 1243 cm^?1, and 1282 cm^?1) and C=C (1777 cm^?1) stretching regions. The time-dependent intensities of these RR features, measured with ? 30 ps. resolution, are found (i) to closely correlate with picosecond transient absorption (PTA) data recorded at 575 nm on the same sample and (ii) inversely correlate with the time-dependent intensities of RR bands assigned to the 1¹A_g ground state. Both of these observations support the assignment of these four RR features to the 2¹A_g excited state. These results remove uncertainties associated with earlier experiments in which excited-state RR scattering from (3-carotene was not observed in spite of predicted trends emanating from studies of shorter polyene compounds. The observed C=C band position also agrees with a recent report of this feature.     

Low-spin Manganphthalocyanine: Darstellung,Eigenschaften und elektronisches Raman-Spektrum von Di(cyano)phthalocyaninatomanganat(III) und -(II)

Low Spin Manganese Phthalocyanines: Preparation, Properties and Electronic Raman Spectrum of Di(cyano)phthalocyaninatomanganate(III) and -(II) . Iodophthalocyaninatomanganese(III) reacts with cyanide in acetone to yield di(cyano)phthalocyaninatomanganate(II), in dichloromethane, however di(cyano)phthalocyaninatomanganate(III) is formed. Both complexes are isolated as (n-Bu₄N)-salts. In the cyclovoltammogram the redox couple Mn^II/Mn^III is attributed to E_1/2 = - 0.22 V and the first ringoxidation Pc(2 -)/Pc(1 -) to E_1/2 = 0.75 V. The paramagnetic salts have magnetic moments (μ_eff = 2.11 resp. 2.95 B.M.) typical for the low spin ground state of Mn^II resp. Mn^III (S = 1/2 resp. 1). The uv-vis-nir spectra are discussed. Comparison with the dicyano-complexes of Cr^III, Fe^II/III and Co^III indicates that the multiple “extra bands” between 4 and 23 kK should be assigned to spin allowed trip-multiplets. The vibrational spectra are discussed. ν_as(Mn? C)(a_2u) is found at 350 cm^?1, ν_as(C? N)(a_2u; cyanide) at 2 092 (Mn^II) and 2 114 cm^?1 (Mn^III). The Raman spectra are dominated by resonance Raman(RR) effects. With variable-wavelength excitation polarized, depolarized and anomalously polarized vibrations assigned to phthalocyanine skeletal modes are selectively RR-enhanced for the Mn^II complex. Intensive lines between 1 650 and 3 300 cm^?1 are due to combinations and overtones of the a_2g vibrations at 1 492 and 1 602 cm^?1. In the 10 K Raman spectrum of (n-Bu₄N)[Mn(CN)₂Pc(2 -)] intraconfigurational transitions Γ₁ → Γ₄ and Γ₁ → Γ₃, Γ₅ resulting from the splitting of the ³T_1g ground state of Mn^III (O_h symmetry) by spin-orbit coupling are observed as anomalously polarized and depolarized lines at 172 and 287 cm^?1.     

Resonance Raman spectra of β-carotene and its molecular structure in the excited electronic state

The resonance Raman spectra of β-carotene have been obtained at low temperature. The excitation profiles of ν₁ (1525 cm^?1) and 2ν₁ (3043 cm^?1) are analysed in terms of the Albrecht theory. The overlap integrals between the vibrational wavefunctions of the ground and the first excited electronic states are shown to be the most important factor in determining the resonance Raman intensities of this molecule. Information on the structure of the electronically excited state has been obtained.     

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     

Raman,spectra of matrix-isolated lead molecules

Raman spectra of lead molecules in low-temperature rare-gas matrices show that dimers and larger clusters are isolated. Besides 7 “normal” Raman bands, two strong resonance progressions are found with frequencies of 108.5 and 118.5 cm^?1 in Xe and 111 and 119 cm^?1 in Kr. The 110 cm^?1 peak is assigned to Pb₂, close to the frequency for the X-O⁺_g state of gaseous Pb₂.     

Depolarization dispersion curves of resonance Raman fundamentals of metalloporphyrins and metallophthalocyanines subject to asymmetric perturbations

A model is presented that allows the investigation of depolarization dispersion curves of a_1g,a_2g,b_1g and b_2g resonance Raman fundamentals in the region of the Q state of metalloporphyrins and metallophthalocyanines. This dispersion results from electronic and/or vibronic perturbations of A_2g,B_1g and B_2g symmetry due to asymmetric substituents and/or metal ion-ring interaction acting on the porphyrin (phthalocyanine) ring. The electronic perturbations affect the electronic configuration interaction pattern between the four orbital components of the Q and B states, yielding thereby similar depolarization dispersion curves for all modes of a given symmetry, whereas the vibronic perturbations affect selectively the vibronic coupling matrix of a particular mode. Depolarization dispersion curves resulting from A_2g and B_1g perturbations are treated separately, and many helpful perturbational formulas are given for use in analyzing experimental data. Examples of depolarization dispersion curves and excitation profiles of fundamentals of a_1g, a_2g, b_1g and b_2g symmetry are presented. It is shown that strong depolarization dispersion observed in copper chelate of mesoporphyrin IX dimethyl ester for a_1g and a_2g fundamentals can be explained in terms of an A_2g electronic perturbation and a vibronic a_2g perturbation suffered by the a_1g(1131 cm^?1) fundamental. Similarly, the depolarization dispersion curves observed for fundamentals in cytochrome c and Pt-phthalocyanine are explained in terms of an electronic B_1g perturbation, together with selective b_1g vibronic perturbations acting on the 1310 cm^?1 a_2g fundamental in cytochrome c and the 482 cm^?1 b_2g fundamental in Pt-phthalocyanine. The agreement between the depolarization dispersion curves predicted by our model and experimental data is shown to be satisfactory.     

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.     

Theory of depolarization dispersion of inversely polarized modes in heme proteins

A new polarization phenomenon observed recently in resonance Raman scattering from heme proteins is explained by vibronic interactions between split Q_x, Q_y, and B_x, B_y electronic states in porphyrin rings. Analytical formulas are presented which account well for the observed depolarization dispersion of the 1585 cm^?1 and 1310 cm^?1 a_2g modes in ferrocytochrome c.     

Electronic structure of Re2Cl82−

The multiple scattering Xα method has been used to calculate the ordering of both occupied and unoccupied one-electron energy states of Re₃Cl₈^2?. Single crystal polarized electronic spectra of [(n-C₄H₉)₄N]₂[Re₂Cl₈] have been measured at 5 K. Principal band maxima are observed at 14 180 (z), 30870 (xy), and 39 215 (z) cm^?1. The calculation, observed polarizations, and a comparison of band positions in Re₂Cl₈^2? and Re₂Br₈^2? suggest the following transition assignments for the former complex: 14 180 cm^?1, b_2gδ → b_1uδ*; 30 870 cm^?1, e_g → b_1uδ*; 39 215 cm^?1, e_uπ → e_gπ*.     

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.     

Darstellung und Charakterisierung der Pentammin-Komplexe [Os(NH3)5(NCS)]2+ und [Os(NH3)5(NCSe)]2+

Preparation and Characterization of the Pentammine Complexes [Os(NH₃)₅(NCS)]²⁺ and [Os(NH₃)₅(NCSe)]²⁺ The new pentammine complexes [Os(NH₃)₅(NCS)]²⁺ and [Os(NH₃)₅(NCSe)]²⁺ are prepared from the reaction of [Os(NH₃)₅(CF₃SO₃)](CF₃ SO₃)₂ with NH₄SCN and KSeCN, respectively, in acetone, and subsequent purification by ion exchange chromatography on carboxymethyl cellulose. Evidence of N-bonding in both cases is given by the vibrational spectra, indicating that Os³⁺ is in terms of Lewis acidity harder than Ru³⁺, Rh³⁺, and Ir³⁺. I.r. and Raman spectra are interpreted according to local C_4v symmetry around Os, and the presumed assignments are confirmed by comparison with the i.r. spectra of the perdeuterated compounds. In the electronic spectra of both complexes charge transfer bands at 412 nm (NCS) and 498 nm (NCSe) are observed, respectively. Further weak absorptions near 4500 and 5100 cm^?1, which are in correlation with electronic Raman bands, are assigned to intraconfigurational transitions within the ²T_2g (O_h) ground term, split into three Kramers doubletts by spin-orbit coupling and lowered symmetry. Electrochemical measurements demonstrate a stabilisation of +III and +II oxidation states by π-back donation to —NCS and —NCSe ligands.     

Radical Localization in a Series of Symmetric NiII Complexes with Oxidized Salen Ligands

Square‐planar nickel(II) complexes of salen ligands, N,N′‐bis(3‐tert‐butyl‐(5R)‐salicylidene)‐1,2‐cyclohexanediamine), in which R=tert‐butyl ( 1 ), OMe ( 2 ), and NMe₂ ( 3 ), were prepared and the electronic structure of the one‐electron‐oxidized species [ 1 – 3 ]^+. was investigated in solution. Cyclic voltammograms of [ 1 – 3 ] showed two quasi‐reversible redox waves that were assigned to the oxidation of the phenolate moieties to phenoxyl radicals. From the difference between the first and second redox potentials, the trend of electronic delocalization 1 ^+.> 2 ^+.> 3 ^+. was obtained. The cations [ 1 – 3 ]^+. exhibited isotropic g tensors of 2.045, 2.023, and 2.005, respectively, reflecting a lower metal character of the singly occupied molecular orbital (SOMO) for systems that involve strongly electron‐donating substituents. Pulsed‐EPR spectroscopy showed a single population of equivalent imino nitrogen atoms for 1 ^+., whereas two distinct populations were observed for 2 ^+.. The resonance Raman spectra of 2 ^+. and 3 ^+. displayed the ν_8a band of the phenoxyl radicals at 1612 cm^?1, as well as the ν_8a bands of the phenolates. In contrast, the Raman spectrum of 1 ^+. exhibited the ν_8a band at 1602 cm^?1, without any evidence of the phenolate peak. Previous work showed an intense near‐infrared (NIR) electronic transition for 1 ^+. (Δν_1/2=660 cm^?1, ε=21 700 M ^?1 cm^?1), indicating that the electron hole is fully delocalized over the ligand. The broader and moderately intense NIR transition of 2 ^+. (Δν_1/2=1250 cm^?1, ε=12 800 M ^?1 cm^?1) suggests a certain degree of ligand‐radical localization, whereas the very broad NIR transition of 3 ^+. (Δν_1/2=8630 cm^?1, ε=2550 M ^?1 cm^?1) indicates significant localization of the ligand radical on a single ring. Therefore, 1 ^+. is a Class III mixed‐valence complex, 2 ^+. is Class II/III borderline complex, and 3 ^+. is a Class II complex according to the Robin–Day classification method. By employing the Coulomb‐attenuated method (CAM‐B3LYP) we were able to predict the electron‐hole localization and NIR transitions in the series, and show that the energy match between the redox‐active ligand and the metal d orbitals is crucial for delocalization of the radical SOMO.     

Electronic states of Al2

Ab initio multi-configuration self-consistent field and first-order configuration interaction (FOCI) calculations in an extended basis set have been carried out for the lower energy electronic states of Al₂. The ten core electrons of each Al atom were replaced by an accurate compact effective core potential. The FOCI calculated T_o value for the ³Σ_g^?-³Σ_u^? transition agrees with the experimentally observed emission band to within 90 cm^?1. ³Π_u is calculated to be the electronic ground state of Al₂. Based on FOCI energies and qualitative intensity arguments, the reported optical absorption spectrum of matrix isolated Al₂ also agrees best with a ³Π_u ground state. The ³Σ_g^?1 state is calculated (T_e) at only 324 cm^?1 above the ³Π_u state, and the ¹ΣE_g⁺ state is predicted to lie higher.     

Laser raman spectra of the stable low-temperature phase of ferrocene

Laser Raman spectra of ferrocene crystal are recorded for the stable (orthorhombic) and metastable (triclinic) low-temperature phases, and the stable and undercooled (monoclinic) high-temperature phases.The skeletal vibrational modes [v₄(A_1g) and v₁₆(E_1g)], the CH bending (⊥e) mode [v₂₅(E_2g)], and the lattice modes below 100 cm^?1 show characteristic changes among these phases.     

Near infrared electronic spectrum of TCNQ mono-valent anion

The high resolution near infrared electronic spectrum of TCNQ anion dissolved in 2-methyltetrahydrofuran glass at 77 K has been determined. The absorption bands are interpreted as simple progressions of two molecular vibrations in a single electronic excited state with ν₀₀ = 11661 cm^?1. The molecular vibrations (ω′₁ = 1264 ± 3 cm^?1, ω′₂ = 335 ± 3 cm^?1) of the vibrational progression agree well with observed Raman active transitions. The experimental data do not require the presence of two electronic transitions in the 1.3 to 2.1 eV region, contrary to what had been assumed previously on the basis of less well resolved room temperature spectra.