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 T3 (π, π) State of acridine

The 00 band maximum of the transition T₃(π, π^*) ← T₁ (π, π^*) of acridine occurs at ≈ 10200 ± 20 cm^?1 in inert (n-hexane, benzene, CCl₄), at 10220 ± 20 cm^?1 in polar (acetonitrile) and at 10170 ± 50 cm^?1 in hydrogen-bonding (methanol, 2-propanol and alkaline water) solvents. Based on the solvent-independent energy of T₁ (π, π^*), the T₃(π, π^*) state of acridine is estimated at 26050 ± 50 cm^?1 in all the solvents.     

Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Strongly enhanced N₂ first positive emission N₂(B ³Π_g → A ³Σ⁺_u) has been observed on addition of N atoms into a flowing mixture of Cl and HN₃. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N₃ → N₂(B ³Π_g) + N₂(X ¹Σ⁺_g) of _i(1.6 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1. That for the reaction Cl + HN₃ → HCl + N₃ is (8.9 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1 from the decay of the emission. Comparison of the emission intensity in ClHN₃ with that in ClHN₃N gave the rate constant of the reaction N₃ + N₃ → N₂(B ³Π_g) + 2N₂(X ¹Σ⁺_g) as 1.4 × 10^?12 cm³ molecule^?1 s^?1 on the assumption that N + N₃ yields only N₂(B ³Π_g) + N₂(X ¹Σ⁺_g).     

Dynamic jahn-teller effect in a ligand-field excited state of MnO3−4 in Sr5(PO4)3Cl

The ³A₂ → ³E (³T₂) band system of MnO^3?₄ in Sr₅(PO₄)₃Cl at 4.2 K between 10000 and 12000 cm^?1 consists of a single progression with 18 components (average frequence 94.5 cm^?1) and a double-humped distribution of Franck-Condon factors. as predicted for the vibronic interaction of an E electronic state with an e vibrational mode.     

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)].     

Electronic absorption spectrum of Fe3+ doped in ammonium chloride single crystal

The electronic absorption spectrum of the Fe²⁺ ion doped in ammonium chloride has been studied at room and liquid air temperatures. The observed bands have been assigned transitions from the ground ⁶A_1g(S) state to the excited ⁴A_1g(⁴E_g), ⁴T_1g(G) and ⁴T_2g(G) states. The cubic field approximation with D_q = 675 cm^?1, B = 645 cm^?1 and C = 4.4 B is found to give a good fit to the observed band positions.It is further concluded that the site symmetry of the Fe³⁺ ion in the crystal is lowered from O_h to C_4v symmetry at liquid air temperature.     

Low temperature luminescence spectra of the d10s2 complexes Cs2MX6 (M = Se,Te and X = Cl,Br). The Jahn—Teller effect in the Γ−4(3T1u) excited state

The emission spectra of the title compounds in microcrystalline form have been measured at 10 K. The extensive vibrational progression in the e_g mode is indicative of a tetragonal Jahn—Teller distortion in the Γ^?₄(³T_1u) excited state. The vibronic coupling of a threefold electronic state with a doubly degenerate e_g mode (T—e coupling), linear in the nuclear coordinates, has been reinvestigated considering spin—orbit coupling up to second order perturbation on energy levels which result from an a¹_1gt¹_1u electron configuration. For an estimation of Jahn—Teller coupling constants, the intensity distributions in the progressions were compared with the theoretical line shape functions which were obtained from a model which also permits the determination of potential energy minima and vibrational fundamentals of the excited state. The unusually large increase in the e_g vibrational frequency compared to the ground state is due to Jahn-Teller forces which distort the potential surface, yielding steeper excited state energy curves.     

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 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*.     

Tunable biode laser high resolution spectroscopy of the ν3 vibration of matrix isolated SO2

True lineshape of the ν₃(b₁) vibrational transition of ³²SO₂ isolated in an Ar matrix was measured with a high resolution (< 10^?3 cm^?1) tunable diode laser spectrometer and temperature effects on line frequencies and linewidths are reported.     

b 1Σ+ emissions from group V-VII diatomic molecules: bo+ → X10+, X21 emissions of SbBr

Chemiluminescence studies of the reactions of microwave-discharged oxygen with SbBr₃ have led to the observation of some band sequences in the near infrared region which are attributed to b0⁺ → X₁0⁺ and b0⁺ → X₂1 transitions of SbBr. Analysis of the spectra yielded T_e values for the X₂1 and b0⁺ states of 874 ± 10 and 12756 ± 10 cm^?1, respectively, and vibrational frequencies in the X₁0⁺, X₂1 and b0⁺ states of ω′'_e(X₁, X₂) = 257 ± 10 and ω′_e(b) = 270 ± 10cm^?1.     

Die Feinstruktur in den Schwingungs- und elektronischen Absorptionsspektren von [CrO4]2− und [MnO4]−

Finestructure in the Vibrational and Electronic Absorption Spectra of [CrO₄]^2? and [MnO₄]^? The ir and ra spectra of Tl₂[CrO₄] and (C₂H₅)₄N[MnO₄] are measured and assigned. Details of the preresonance- and resonance-Raman effect are discussed. The exact knowledge of the vibrational spectrum enables the understanding of the complicated vibrational finestructure in the electronic absorption spectrum of (C₂H₅)₄N[MnO₄]. For the states of the charge-transfer t₁ → e* bands are found at 15 000, 15 170 cm^?1 for ¹T₁(I), at 17 646, 17 708, 17 809 cm^?1 for ¹T₂(II) and at 17 920, 17 992 and 18 080 cm^?1 for ³T₂(III). The electronic origin for the states of the t₂ → e* chargetransfer is at 24 661 for ¹T₁(IV) and 30 230 cm^?1 for ¹T₂(V). The vibrational coupling is only with the totally symmetric Mn? O-stretching-vibration. Bands at 29 500 cm^?1 and 44 450 cm^?1 are assigned to the ¹T₂-states of the t₁, t₂ → t₂* charge-transfer.     

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.     

Vibrational energy transfer from N2 to CO on electron excitation of N2-CO solids at 4.2 K

Spectra emitted from 0.1% CO-N₂ solids excited with high energy electrons at 4 K show evidence for resonant transfer of vibrational energy from highly excited vibrational levels of N₂ to CO in the process N₂(X¹Σ_g⁺, ν) + CO(ν = 0) → N₂(X¹Σ_g⁺, ν - 1) + CO(ν = 1) + phonons. Energy transfer from levels with ν ? 9 has been observed.     

Diffusion coefficient measurement of O*2(1Δg) in ground state O2

The diffusion coefficient of O_*2(¹Δ_g) in O₂(³Σ^?_g) has been measured as a function of pressure, D^* = 0.201 ± 0.005 cm² s^?1 at 1 atmosphere and 298 K.     

Relaxation mechanism of the 1Δg state of liquid O2

Collisional deactivation of the first excited electronic ¹Δ_g(υ = 0) state of O₂ involves intersystem crossing to higher vibrational levels (υ < 5) of the electronic ground state ³Σ^?_g. It is followed by rapid vibrational-vibrational energy exchange which populates the first excited ³Σ^?_g(υ = 1) vibrational level. The suggested relaxation mechanism is supported by experimental results on the time dependence of the populations of the ¹Δ_g(υ = 0) and ³Σ^?_g(υ = 1) states in liquid natural O₂ and ¹⁸O₂.     

Vibrational emission of NO2 from the reaction of NO with O3

Vibrational chemiluminescence in the Δν₁ = Δν₃ = ?1 band of NO₂ is observed both in the O + NO and O₃ + NO reactions and shown to be emitted by molecules with up to 11 000 cm^?1 of vibrational energy. Quenching rate constants of NO₂³ are estimated ranging from about 6 × 10^?14 for Ar to about 3 × 10^?12 cm³ s^?1 for NO₂. The ratio of vibrational to electronic emission is 0.06 ± 0.03 for O + NO and 5.3 ± 1.0 for O₃ + NO. It is suggested that vibrationally excited NO₂ is a major product of that channel of the O₃ + NO reaction which forms ground-state NO₂(²A₁) directly.     

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.     

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.     

b 1Σ+ and a 1Δ emissions from group VI—VI diatomic molecules: b0+ → X10+, X21 emissions of TeSe

Near-infrared emissions of the b0⁺ → X₁0⁺, X₂1 band systems of TeSe have been observed in a discharge flow system. Analysis of the spectra yielded T_e values of the X₂1 and b0⁺ states of 1235 ± 5 cm^?1 and 8794 ± 5 cm^?1, respectively, and a vibrational spacing in the b0⁺ state of ω_e(b) = 294 ± 3 cm^?1.