Vibrational spectra of tropylium tetrahaloborates [C7H7] [BX4] (X  Br or I)

Raman and i.r. studies of the title compounds, which are salts of the planar D_7h tropylium cation, provide complete sets of vibrational frequencies for the tetrahaloborate anions, including Raman data for [BI₄]⁻ for which ν₁(a₁) = 169, ν₂(e) = 83, ν₃(t₂) = 515 (¹¹B), 543 (¹⁰B) and ν₄(t₂) = 117 cm⁻¹.     

Raman analysis of SF6 molecular beams excited by a cw CO2 laser

In a molecular beam the effects of vibrational pumping of SF₆ (ν₃ = 948 cm^?1) are studied, using a line-tunable cw CO₂ laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (x_E/D ≤ 1), a thermal redistribution of the ν₃ excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm^?1. For excitation in the relatively rare collision regime (x_E/D ? 4), a structured non-thermal ν₁ Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν₃ mode. The value of T_rot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν₃(948 cm^?1)+ΔE_rot → h(ν₄ + ν₆)(962 cm^?1) relative to the near-resonant transfer rate (hν₃ + hν₃ → 2hν₃ + 3.5 cm^?1)].     

Darstellung und spektroskopische Charakterisierung der Nona-halogenodiiridate(III), [Ir2X9]3−, X = Cl,Br

Preparation and Spectroscopic Characterization of Nonahalogenodiiridates(III), [Ir₂X₉]^3?, X = Cl, Br The pure nonahalogenodiiridates(III), A₃[Ir₂X₉] (A = K, Cs, tetraalkylammonium; X = Cl, Br) have been prepared. They are formed from the monomer hexahalogenoiridates(III) which are bridged to confacial bioctahedral complexes by ligand abstraction in less polar organic solvents. The IR and Raman spectra exhibit bands in three characteristic regions; at high wavenumbers stretching vibrations with terminal ligands ν(Ir?Cl_t): 360?300, ν(Ir?Br_t): 250?220; in a middle region with bridging ligands ν(Ir?Cl_b): 290?235, ν(Ir?Br_b): 205?190 cm^?1; the deformation bands are observed at distinct lower frequencies. The distance between ν(Ir?X_t) and ν(Ir?X_b) increases with decreasing size of the cations. The electronic spectra measured at thin films of the pure complex salts at 10 K show some intensive charge transfer transitions in the UV and one or two weak d? d bands in the visible region.     

The B̃2B1 ← X̃2A1 absorption system of NO2 in Xe matrices: evidence for Renner—Teller interaction

A tentative vibrational assignment of the B?²B₁ ← X?²A₁ absorption system of NO₂ in solid Xe is reported. About 65 bands were analysed, yielding normal vibration energies of ν₁ = 1230, ν₂ = 450 and ν₃ = 2040 cm^?1. The electronic transition energy can be estimated to be T₀₁₀ = 14160 cm^?1 (14220 cm^?1 for the gaseous phase). These observations are in good agreement with predictions made using ab initio calculations. Evidence for Renner—Teller interaction is documented by a systematic staggering of frequency intervals between successive bands in the ν₂ progression of the B? state.     

Study of the Fermi doublet ν1 — 2ν2 in the Raman spectra of CO2 in different phases

The relation between the intensity ratio R and the frequency separation Δ of the Fermi doublet components ν₊ and ν₋ in the Raman spectra of CO₂ in dense gas, liquid, solid and aqueous solutions is used to establish the correct assignment of the levels to ν₁ and 2ν₂. The unperturbed fundamental ν⁰₁ is at higher frequency than 2ν⁰₂ in all the phases studied. The values of ν⁰₁ increase and of 2ν⁰₂ decrease with pressure. The values of W and K₁₂₂ are nearly constant for the dense gas, liquid and solid in the pressure range of 6–44 kbars, but decrease in the solid for pressures up to 100 kbars and also in aqueous solutions.     

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.     

Raman study of the molecular motions of pivalic acid: the liquid—plastic phase transition

Raman spectra of pivalic acid in the plastic and liquid phase have been measured. The reorientational correlation times have been evaluated from the ν_asCH, νCO and νCC bands as a function of temperature. The reorientational correlation time corresponding to ν_as CH and νCC bands is τ < 10⁻¹¹ s whilst for the νCO band τ = 4ps (T = 20°C). The calculated activation energy is 26 KJ mol⁻¹. The reorientation of the carboxylic groups which may be assisted by the proton transfer along the hydrogen bonds in dimers is discussed.     

A Raman spectroscopic study of the mineral coquandite Sb6O8(SO4)·(H2O)

Raman spectra of coquandite Sb₆O₈(SO₄)·(H₂O) were studied, and related to the structure of the mineral. Raman bands observed at 970, 990 and 1007 cm^?1 and a series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes respectively. Raman bands at 629, 638, 690, 751 and 787 cm^?1 are attributed to the SbO stretching vibrations. Raman bands at 600 and 610 cm^?1 and at 429 and 459 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes. Raman bands at 359 and 375 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure.     

Darstellung und Charakterisierung von bindungsisomeren Hexakis(thiocyanato-isothiocyanato)-iridaten(III) und einiger Chloro-, Cyano-pentarhodanoiridate(III)

Preparation and Characterization of Bond-Isomeric Hexakis(thiocyanato-isothiocyanato)-iridates(III) and Some Chloro-, Cyano-pentarhodanoiridates(III) The evaporated ethanolic extract of the reaction product of K₃[IrCl₆] and HNO₃, refluxed with an aqueous KSCN solution yields a mixture of the bond isomers [Ir(NCS)_n(SCN)_6?n]^3?, n = 0–2 and small amounts of bond isomeric chloropentrahodanoiridates(III). By heating the tetrabutylammonium salts, N coordination of the ambident SCN^? is favoured forming compounds with n = 2–5 beside chloro- and cyanopentarhodanoiridates(III). With n = 2, 3 pairs of geometric isomers can be detected. The pure compounds are separated by ion exchange chromatography on diethylaminoethylcellulose. The trans/mer-complexes migrate 1.9 times faster than the cis/fac-isomers. Depending on S- or N-bonding the IR and Raman spectra show typical vibrations: ν_CN(N) and ν_CN(S): 2100–2175, ν_CS(N): 810–855, ν_CS(S): 690–710, δ_NCS: 470–480, δ_SCN: 420–470, ν_IrN: 300–325, ν_IrS: 255–313 cm^?1. Except the inner ligand vibrations the Rh? N and Rh? S valence frequencies are assigned according to the supposed point symmetries. By interaction of the trans-positioned ligands characteristic shifts are caused.     

Darstellung und Charakterisierung von bindungsisomeren Hexakis-(thiocyanato-isothiocyanato)-rhodaten(III) und Di-μ-thiocyanato-N,S-octathiocyanatodirhodat(III)

Preparation and Characterization of Bond-Isomeric Hexakis-(thiocyanato-isothiocyanato)rhodates(III) and Di-μ-thiocyanato-N, S-octathiocyanatodirhodate (III) The reaction of RhCl₃ with an aqueous solution of KSCN does not yield pure [Rh(SCN)₆]^3? as is supposed until now but a mixture of the bond isomers [Rh(NCS)_n(SCN)_6?n]^3?, n = 0–3. By heating the tetrabutylammonium salts N coordination of the ambident SCN^? is favoured forming mixtures with n = 0–4. The pure bond isomers are separated by ion exchange chromatography on diethylaminoethyl cellulose. Extracting the mixture (n = 0–3) with triphenylphosphiniminiumchloride from water into CH₂Cl₂ [Rh₂(SCN)₁₀]^4? is formed, containing two Rh? SCN? Rh bridges and exclusively S-coordinated terminal ligands. Depending on S or N bonding the IR and Raman spectra show typical vibrations: ν_CN(N) and ν_CN(S): 2095–2170, ν_CS(N): 810–835, ν_CS(S): 695–710, δ_NCS: 460–470, δ_SCN: 425–465, ν_RhN: 300–340, ν_RhS: 265–306 cm^?1. The application of group theory indicates that for n = 2 and 4 the cis-, for n = 3 the mer-compound exists. Except the inner ligand vibrations the Rh? N and Rh? S valence vibrations are assigned according to the supposed point symmetries. By interaction of trans-positioned ligands characteristic shifts are caused. The isolated complexes may also be distinguished and identified by their electronic spectra.     

On spectroscopic properties and isotope effects of vibrationally stabilized molecules

Results of quantum and semiclassical calculations obtained for two different potential-energy surfaces are used to discuss spectroscopic properties and isotope effects of the linear IHI and IDI molecules. The potentials are a purely repulsive LEPS surface and a DIM-3C potential with two van der Waals type minima for equivalent IH ··· I and I ··· HI configurations. Both systems are dominated by the effect of vibrational bonding giving rise to some very unusual spectroscopic phenomena, which are discussed in detail. The different vibrational frequencies and rotational constants are roughly estimated as ν₁ = 120 (100) cm^?1, ν₂ = 280 (210) cm^?1, ν₃ = 360 (160) cm^?1 and B = 0.0194 (0.0196) cm^?1 for IHI (IDI). A detailed discussion of the dependence of ν₁, ν₂ and B on ν₃, their sensitivity to variations of the potential-energy surface, and a comparison with the vibrational frequencies of I₂ and HI (ID) is given. It is predicted that there exists only one excited level of the antisymmetric stretching mode. The numbers of symmetrical stretching and bending levels are fairly constant or may even decrease upon deuteration. Simultaneously deuteration destabilizes the molecule. These unusual phenomena are rationalized by our calculations. A set of criteria for observing infrared and Raman bound-to-bound and bound-to-resonance state transitions are presented for the IHI and IDI molecule.     

Vibrational energy transfer in CH2F2

Infrared fluorescence has been observed from the ν₁, ν₆, 2ν₉, ν₈ and ν₄ levels of CH₂F₂ following excitation by a 9.6 μ Q-switch CO₂ laser. All the observed states exhibit a single exponential decay rate of approximately 44 msec^?1 torr^?1. The rare gas dependence of this rate has also been measured and found to be up to 20 times slower than the rate for the pure gas. Measurements of the risetimes of the observed fluorescence signals yielded an upper limit of 5 μsec at 1 torr for the ν₁, ν₆ and ν₈ levels. The 2ν₉ and ν₄ risetimes were effectively instantaneous under the experimental conditions that prevailed. The relative magnitudes of the measured rate are discussed in terms of existing V-T/R theories and collisional energy transfer processes.     

Lifetimes of C-2 in rotational levels of the B̃2Σ+u state in the gas phase

Lifetimes of C^-₂ in rotational levels of the B?²Σ⁺_u:ν′ = 0, ν′ = 1 states have been measured. C^-₂ was produced from bromoacetylene and rare-gas metastables and the B?²Σ⁺_u—X?²Σ⁺_g transition was laser excited. The lifetimes are constant within a vibrational level, 77 = 8 ns for ν′= 0 and 73 = 7 ns for ν′ = 1. The oscillator strength f_νo = 0.044 ± 0.004.     

An ab initio calculation of the potential surface and rotation—vibration energies of the silyl radical

We have calculated 64 points on the ground electronic state potential energy surface of the silyl radical (SiH₃) using the MRD CI technique. This potential surface gives an inversion barrier of 1951 cm^?1 and an equilibrium geometry of r_e = 1.480 Å and α_e(HSiH) = 111.2°. Using the non-rigid invertor Hamiltonian with this potential we determine for SiH₃ that ν₁ = 2424 cm^?1, ν₂ = 778 cm^?1, ν₃ = 2106 cm^?1, and ν₄ = 976 cm^?1; the inversion splitting is calculated to be 0.11 cm^?1. Rotational constants and centrifugal distortion constants have also been calculated.     

The ab initio calculation of the band origin and vibrational frequencies of the Ã-X̃ system of HNCl using the non-rigid bender hamiltonian

A three-dimensional fit of ab initio MRD CI potential data has been made for the lowest two electronic states of the HNC1 molecule (X̃ ²A″ and à ²A'), and the corresponding vibrational frequencies and rotational energies have been computed using the non-rigid bender Hamiltonian. For the ground state the vibrational frequencies obtained are ν₁ = 2942 cm⁻¹, ν₂ = 1232 cm⁻¹, and ν₃ = 549 cm⁻¹, while the corresponding values for the first excited state are 3524,947 and 836 cm⁻¹ respectively. We calculate T_c(à ²A') 16200 cm⁻¹, T_o(òA') = 16400 cm⁻¹, and the Franck-Condon maximum, Ã(0,3,1)-X̃(0,0.0), is calculate at 19200 cm⁻¹(5200 Å).     

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.     

Measurement of longitudinal optical mode frequencies of alkali metal and alkaline earth nitrates and carbonates by PSR infrared spectroscopy

Polarized specular reflectance (PSR) infrared spectroscopy was employed to determine the longitudinal optical mode frequencies of alkali metal and alkaline earth nitrates and carbonates. PSR spectra of AgNO₃, TlNO₃, and Pb(NO₃)₂ also are reported. Approximate values of |?μ/?Q| were calculated for the ν₂(A″₂) and ν₃(E′) modes of NO^?₃ and CO^2?₃ ions from the observed frequencies.     

Rate constants of the near-resonant E-E energy exchange processes SeS(b0+) + O2(X3Σg−) ⇌ SeS(X10+) + O2(a1Δg)

SeS radicals generated in a fast flow system were excited to their b0⁺, ν' = 0 vibronic state by absorption of Raman-shifted dye laser pulses at 1280 nm. From time-resolved measurements of the b0⁺ → X₁0⁺ fluorescence as a function of added gas pressure, the radiative lifetime of the b0⁺ = 0 state (τ₀ = 400 ± 100 μs) and quenching rate constants for H₂, D₂, N₂, CO, O₂, and CO₂ were deduced. Quenching of SeS(b0⁺, ν'= 0) by O₂ is attributed to the near-resonant electronic- to-electronic energy-transfer process (1), SeS(b0⁺, ν'₁ = 0) + O₂(X³Σ_g⁻, ν″₁ = 0) ⇌ SeS(X₁0⁺, ν″_f = 0) + O₂(a¹Δ_g, ν'_f = 0)−77 cm⁻¹, for which (k₁ = (1.4±0.3) × 10⁻¹² cm³ s⁻¹ was obtained. On the assumption of detailed balancing, k₋₁ was calculated to be (3.0 ± 0.7) × 10⁻¹²cm³ s⁻¹.     

Observation of nonlinear molecular hyperfine level crossings in CD3I

Level crossings between hyperfine levels were observed in the nonlinear absorption of CD₃I ν₂^QP(4,1) transition by using the P(16) laser line of the CO₂ 10.6 μm band. From the electric fields of crossings, the dipole moments of this molecule were determined. These are μ₀ = 1.6514 ± 0.0025 and μ₁ = 1.6477 ± 0.0025 debye, in the ground state and in the ν₂ state, respectively.     

Vibrational-translational/rotational and vibrational-vibrational processes in methane: Optoacoustic measurements

Both V-T,R and V-V processes in methane have been studied optoacoustically following excitation of the ν₃ level with a He-Ne laser at 2947.9 cm^?1. The lifetime of the V-T,R process is 1.55 ± 0.05 μs atm. The rate constants for the fast equilibration between the bending modes is k(ν₂ → ν₄) = 60 μs^?1 atm^?1 and k(ν₄ → ν₂) = 13 μs^?1 atm^?1. The decay of the ν₃ and ν₂ stretching modes, which are in very rapid equilibrium, shows a rate constant of 0.23 ns^?1 atm^?1 and, within experimental error, produces exclusively the ν₄ stretching mode. Part of this decay, 4.6%, is by a single-quantum process producing a large amount of translational/rotational energy; the dominant process, 95.4%, is double-quantum through the 2ν₄ overtone. Both the yield of the single-quantum process and the exclusive production of the ν₄ bending mode from the (ν₃, ν₂) level are in dispute with current theoretical models.