Interstate coupling and dynamics of excited singlet states of isolated diphenylbutadiene

In this paper, we report on absolute fluorescence quantum yields from photoselected vibrational states of jet-cooled 1,4-diphenylbutadiene for excess vibrational energies, E_v = 0−7500 cm⁻¹, above the apparent electronic origin of the S₁(2A_g) state. The pure radiative lifetimes, τ_r, of the strongly scrambled S₂(1B_u)—S₁(2A_g) molecular eigenstates (E_v = 1050−1800 cm⁻¹) show a marked dilution effect, (τ_r/τ_r(S₂) ≈ 40), being practically identical with the τ_r values from the S₁(2A_g) manifold (E_v = 0–900 cm⁻¹), which is affected by near-resonant vibronic coupling to S₂(1B_u) and exhibiting the dynamic manifestations of the intermediate level structure. Isomerization rates in the isolated molecule, which do not exhibit vibrational mode selectivity, were recorded over the energy range 0–6600 cm⁻¹ above the threshold.     

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.     

Syntheses and structures of two new M6Li8(N3)a6 cluster-unit based compounds: Cs4Re6S8(N3)6·H2O and Na2Mo6Br8(N3)6·2H2O

The two new cluster compounds, Cs₄Re₆S₈(N₃)₆·H₂O (1) and Na₂Mo₆Br₈(N₃)₆·2H₂O (2), have been prepared via solution chemistry route, starting from the Cs₄Re₆S₈Br₆CsBr and Mo₆Br₁₂ precursors synthesized by solid state chemistry techniques, and structurally characterized (crystal data: Cs₄Re₆S₈(N₃)₆·H₂O (1): Orthorhombic, space group Pnam, a=10.0651(1) Å, b=15.8856(2) Å, c=20.1714(3) Å, V=3225.2(7) Å³, Z=4, d_calc=4.48 g cm⁻³, μ=27.43 mm⁻¹; Na₂Mo₆Br₈(N₃)₆·2H₂O (2): Orthorhombic, space group Ibam, a=11.5643(3) Å, b=14.3959(5) Å, c=17.0340(7) Å, V=2835.8(2) ų, Z=4, d_calc=3.63 g cm⁻³, μ=13.91 mm⁻¹). Their structures revealed that in both cases, the M₆Lⁱ₈ cluster core remains unchanged in the starting and final compounds whereas the bromine apical ligands (Br^a) are substituted by N₃ azide groups leading to M₆Lⁱ₈(N₃)^a₆ cluster unit. The new Cs₄Re₆S₈(N₃)₆·H₂O is the first example of a compound containing an octahedral rhenium cluster coordinated to azide groups.     

High resolution Fourier transform spectroscopy of the PbO molecule from investigation of the O2(1Δg)—Pb reaction

From the reaction of Pb with metastable oxygen O₂(¹Δ_g) in a Broida type oven we have analysed at high resolution some vibrational levels of the X0⁺, a1, A0⁺ and B1 states of the ²⁰⁸PbO molecule. The rotational parameters determined allowed us to recalculate the position of the various isotope lines to within 0.01 cm⁻¹. We have found a negative value of ω_eχ_e (−0.123 (25) cm⁻¹) in A0⁺, contrary to previous observations. The Ω type doubling in a1 varies from +1.8 × 10⁻⁴ cm⁻¹ (υ′ = 2) to +2.3 × 10⁻⁴ cm⁻¹ (υ′ = 9) and in B1 from −1.17 × 10⁻⁴ cm⁻¹ (υ′ = 0) to −0.97 × 10⁻⁴ cm⁻¹ (υ′ = 2).     

Structure et étude raman du composé (C3H7NH3)2HgCl4

The structure of (C₃H₇NH₃)₂HgCl₄ is orthorhombic, M_r = 462.6, Abma, a = 7.991(2) Å, b = 7.779(2) Å, c = 23.519(2) Å, Z = 4, V = 1462(1) ų, D_m = 2.05(2), D_x = 2.10 mg/m⁻³, λ(AgKα) = 0.56083 Å, μ(AgKα) = 61.02 cm⁻¹, T = 300 K, R = 0.032, R₂ = 0.027 for 1188 reflections with I < 0.5σ(I). The structure is of the K₂NiF₄ type and consists of HgCl₆ octahedra which are held together through equatorial Cl atoms forming a two-dimensional (HgCl₄)²⁻_n layer perpendicular to the c axis (HgCl_ax is shorter than the HgCl_eq). The C₃H₇NH⁺₃ cations inserted between these layers are disordered and joined to the layers by hydrogen bonding. The Raman spectra between 10 and 400 cm⁻¹ have been recorded and some characteristic (HgCl₄)²ⁿ⁻_n layer frequencies assigned. Thermal analysis indicates two singularities at 195 and 205 K.     

Vibrational (i.r. and Raman) spectra and conformational studies of 1-formyl-3-thiosemicarbazide

The i.r. and Raman spectra (30–4000 cm⁻¹) of 1-formyl-3-thiosemicarbazide (FTSC) and deuterated ftsc-d₄, have been studied. Most of the vibration modes reveal pairs of bands and show strong temperature dependence. A band group {ν(NNH₂)} at ∼ 1100 cm⁻¹ exhibits well resolved doublet (1095 and 1112 cm⁻¹) structure below 100 k. The intensity in the 11 12 cm⁻¹ band decreases regularly (band disappears at 150 K) with the rise in temperature. Two new bands at 955 and 1070 cm⁻¹ appear while measured above 400 K. The system eventually exists in several conformers in simultaneous equilibria. Moreover, a few bands {e.g. ν(CO), ν(CS) and ν(CH)} that show strong intensifies in i.r. exhibit weak (or zero) intensifies in the Raman and vice-versa. The features (characteristic of u and g vibration species) could be explained by a C_2h pseudo symmetry space group proposed for the system. Both the FTSC and FTSC-d₄ represent strong molecular associations. This favours the maximum abundance in the dimer stabilized conformers.     

Highly resolved polarized absorption spectra of single-crystal [Ru(bpy)3](PF6)2

Polarized absorption spectra of neat single-crystal [Ru(bpy)₃](PF₆)₂ at 300 and 5 K are presented. The spectra show pronounced vibronic structure and it is possible to assign the vibrations to known Raman frequencies. Furthermore, the different electronic states corresponding to the vibronic transitions are identified and assigned. The assignment of the lowest excited states - observed in absorption - agrees with an earlier classification of the emitting states. In particular, the E ⊥ c-polarized transition A'₁ ⇌ 2E' (classified in D'₃), at 17816 cm⁻¹, is found at the same energy (experimental error: ± 1 cm⁻¹) in emission and absorption and represents a zero-phonon, zero-vibron transition. The low-energy part of the E¦¦_c-polarized spectrum (below ≈ 24000 cm⁻¹) is not dominated by a series of different electronic states but by a 1600 cm⁻¹ progression with zero-vibron transition at 18770 cm⁻¹.     

New electronic transitions observed in the trinuclear iron (III,III,II) cluster,by inelastic neutron scattering

The incoherent inelastic neutron scattering (IINS) spectrum of the iron (III, III, II) complex [Fe₃O(OOCMe)₆(py)₃](py) shows a pair of magnetic transitions at 199 and 221 cm⁻¹. These are assigned to an exchange-coupled doublet, originating from the transition |S, S_ab> = | 1, 1 > → | 2, 2 >, which from previous IINS spectra were predicted to occur at 209 cm⁻¹.     

Darstellung von trans-[Pt(N3)4X2]2− (X = Br,I, SCN,SeCN) durch oxidative Addition an [Pt(N3)4]2− in organischen Lösungsmitteln

Preparation of trans-[Pt(N₃)₄X₂]^2? (X ? Br, I, SCN, SeCN) by Oxidative Addition to [Pt(N₃)₄]^2? in Organic Solvents By oxidative addition to (TBA)₂[Pt(N₃)₄], dissolved in dichlormethane, trans-(TBA)₂[Pt(N₃)₄X₂], X ? Br, I, SCN, SeCN; TBA = Tetrabutylammonium, are formed. The vibrational spectra of these salts are assigned according to point group D_4h. From the resonance Raman spectrum of trans-(TBA)₂[Pt(N₃)₄I₂] the harmonic vibrational frequency ω₁ of v(Pt? I), A_1g, is calculated to be 138.50 cm^?1 and the inharmonicity constant x₁₁ = 0.27 cm^?1. The characteristical feature in the UV/VIS spectra is caused by intensive π(N,X) → a_1g, b_1g(Pt) CT transitions.     

Cavity ring‐down spectroscopic study of the kinetics of the reactions of FCO radicals with O2 and NO at 295 K

Cavity ring‐down UV absorption spectroscopy was used to study the kinetics of the recombination reaction of FCO radicals and the reactions with O₂ and NO in 4.0–15.5 Torr total pressure of N₂ diluent at 295 K. k(FCO + FCO) is (1.8 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The pressure dependence of the reactions with O₂ and NO in air at 295 K is described using a broadening factor of Fc = 0.6 and the following low (k₀) and high (k_∞) pressure limit rate constants: k₀(FCO + O₂) = (8.6 ± 0.4) × 10⁻³¹ cm⁶ molecule⁻¹ s⁻¹, k_∞(FCO + O₂) = (1.2 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, k₀(FCO + NO) = (2.4 ± 0.2) × 10⁻³⁰ cm⁶ molecule⁻¹ s⁻¹, and k_∞ (FCO + NO) = (1.0 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. The uncertainties are two standard deviations. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 130–135, 2001     

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.     

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.     

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.     

Single crystal EPR study of Mn(II)-doped magnesium potassium Tutton's salt

Single crystal EPR studies of Mn(II)-doped magnesium potassium Tutton's salt, MgK₂(SO₄)₂.6H₂O, was studied at room temperature. The spin-Hamiltonian parameters obtained are: g=2.0036(3), A = −96(3), D = 350(5), a = 14(2) and F = −5(1) (A, D, a and F are in units of 10⁻⁴ cm⁻¹). The tetragonal distortion axis corresponds to one of the MgO bond directions. The zero-field splitting parameter (D) shows a linear dependence in the temperature range 77–370 K. The percentage of covalency of the MnO bond has been estimated to be 8 per cent.     

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.     

Electronic absorption spectra of M2L6 compounds containing metal-metal triple bonds of σ2π4 configuration

The electronic absorption spectra of compounds containing metal-metal triple bonds of σ²π⁴ valence electronic configuration are presented and discussed. The lowest-energy transition of M₂L₆ compounds (M = Mo or W, L = CH₂Bu^t or OBu^t) is expected to be the dipole-allowed π → π* (e_u → e_g) transition. This appears to be the case for M₂(CH₂Bu^t)₆ and M₂(OBu^t)₆ compounds, in which the lowest energy absorption bands occur between 26,000 and 28,000 cm⁻¹ (ε = 1.1 x 10³-1.8 x 10³ M⁻¹ cm⁻¹). For M₂(NMe₂)₆ compounds, the lowest energy absorption is not the π → π* transition but is assigned instead to a LMCT transition originating from nitrogen lone-pair orbitals, N_1p → π*, observed at 30,800 cm⁻¹ (ε = 1.4 x 10⁴-1.9 x 10⁴ M⁻¹ cm⁻¹). The π → π* transition is not observed in these compounds, but is presumably masked by the more intense LMCT. These assignments are derived from Xα-SW calculations performed and described by other authors (Bursten et al., J. Am. Chem. Soc. 1980, 102, 4579).     

Cavity ring‐down study of BrO radicals: Kinetics of the Br + O3 reaction and rate of relaxation of vibrationally excited BrO by collisions with N2 and O2

Cavity ring‐down (CRD) techniques were used to study the kinetics of the reaction of Br atoms with ozone in 1–205 Torr of either N₂ or O₂, diluent at 298 K. By monitoring the rate of formation of BrO radicals, a value of k(Br + O₃) = (1.2 ± 0.1) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ was established that was independent of the nature and pressure of diluent gas. The rate of relaxation of vibrationally excited BrO radicals by collisions with N₂ and O₂ was measured; k(BrO(v) + O₂ → BrO(v − 1) + O₂) = (5.7 ± 0.3) × 10⁻¹³ and k(BrO(v) + N₂ → BrO(v − 1) + N₂) = (1.5 ± 0.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The increased efficiency of O₂ compared with N₂ as a relaxing agent for vibrationally excited BrO radicals is ascribed to the formation of a transient BrO–O₂ complex. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 125–130, 2000     

New compounds in the cesium sulfobromide rhenium octahedral cluster chemistry: syntheses and crystal structures of Cs4Re6S8Br6 and Cs2Re6S8Br4

The exploration of the CsReSBr system, in order to identify new phases based on octahedral cluster anions, has produced single crystals of Cs₄Re₆S₈Br₆ (1) (trigonal, space group P-6c2, a=9.7825 (3) Å, c=18.7843 (5) Å, V=1556.77 (1) ų, Z=2, density=5.09 g cm⁻³, μ=36.07 mm⁻¹) and Cs₂Re₆S₈Br₄ (2) (monoclinic, space group P2₁/n, a=6.3664 (1) Å, b=18.4483 (4) Å, c=9.3094 (2) Å, β=104.2618 (8)°, V=1059.69 (4) ų, Z=2, density=6.14 g cm⁻³, μ=45.83 mm⁻¹). These two compounds have been obtained by high-temperature solid state route. Their structures have been solved and refined from single crystal X-ray diffraction data. The structure of Cs₄Re₆S₈Br₆ presents isolated anionic cluster units inscribed in a (Cs⁺)₁₂ cuboctahedron and the one of Cs₂Re₆S₈Br₄ exhibits ReS^i-a,a-iRe inter-unit bridges. The framework of the latter presents then a strongly 1-D character.