Temperature dependence of radiationless processes. Isoquinoline in solution

The temperature dependence of the fluorescence quantum yield φ_f, the fluorescence lifetime τ_f, and the oscillator strength f(S₀→S₁) of isoquinoline in solution has been measured between room temperature and 77 K. Following an Arrhenius type expression, φ_f in ethanol increases from 0.012±0.002 at 295 K to 0.61±0.03 at 77 K paralleled by an increase of τ_f from 0.25±0.10 ns to 9.0±0.2 ns. Over the same temperature range f(S₀→S₁) and the radiative fluorescence lifetime remain constant. By analyzing the temperature dependent data, it is shown that a spin-allowed internal conversion process with an activation energy of ～1500 cm^?1 is responsible for the observed temperature effect. A mechanism is proposed based upon a thermally activated depopulation of the S₁(ππ^*) state of isoquinoline via a slightly higher state, presumably the S₂(ππ^*) singlet state. An extremenly fast process involving the dissociation of the hydrogen bond deactivates this latter state, by possing S₁.     

Determination of radiative lifetimes in the 3snp 1 P 1 sequence of Mg I using time-resolved VUV laser spectroscopy

The radiative lifetimes of the states in the (n=5–8) 3snp ¹ P ₁ sequence of neutral magnesium were investigated using time-resolved laser-induced fluorescence. Excitation from the 3s ^{2 1} S ₀ ground state was performed using VUV radiation, which was produced by resonant sum-difference frequency mixing in a krypton gas cell. We find τ(n=5): 54(3) ns, τ(n=6): 140(10) ns, τ(n=7): 290(20) ns. τ(n=8): 475(40) ns. These results were found to be in fair agreement with a Multi Configuration Hartree-Fock (MCHF) calculation.     

The radiative lifetime of the A1II state of BH

Second-order polarization propagator calculations of the X¹Σ⁺ → A¹II transition moment as well as the radiative lifetime of the A¹II state of BH are reported. The calculated vibrational lifetimes are τ(v′ = 0) = 121 ns, τ(v′ = 1) = 129 ns, and τ(v′ = 2) = 137 ns. The τ(v′ = 0 lifetime agrees with the most recent experiment of τ(v′ = 0) = 125 ± 5 ns. We show that the electronic oscillator strength computed at the ground state equilibrium is rather different from the band absorption oscillator strength f₀₀, which demonstrates that theoretical electronic oscillator strengths should not be expected to agree with experimentally determined band oscillator strengths.     

Determination of radiative lifetimes in neutral nitrogen using short laser pulses from a distributed feedback dye laser

Radiative lifetimes were determined for two short-lived states in neutral nitrogen. Following photo-dissociation and two-photon excitation employing the same UV source, excitation to higher states was performed with a distributed feedback dye laser (DFDL). The lifetimes were found to be τ(2p ²4d ⁴ D _7/2)=17(3) ns and τ(2p ²5s ⁴ P _5/2)=22(3) ns.     

Strukturen neuer SeII- und TeII-Komplexe mit 2,2-Dicyanethylen-1,1-dithiolat, 2,2-Dicyanethylen-1,1-thioselenolat und 2,2-Dicyanethylen-1,1-diselenolat

Structures of New Se^II and Te^II Complexes Containing 2,2-Dicyanethylene-1,1-dithiolate, 2,2-Dicyanethylene-1,1-thioselenolate, and 2,2-Dicyanethylene-1,1-diselenolate (NBu₄)₂{Se[S₂C?C(CN)₂]₂} ( I ), (AsPh₄)₂ · {Te[SSeC?C(CN)₂]₂} ( II ), and (NBu₄)₂{Te[Se₂C?C(CN)₂]₂} ( III ) containing the bidentate chelate ligands 2,2-dicyanethylene-1,1-dithiolate i-mnt , 2,2-dicyanethylene-1,1-thioselenolate i-mnts , and 2,2-dicyanethylene-1,1-diselenolate i-mns have been prepared and characterized by X-ray structure analysis. The central units consist of [M(X? X)₂E₂]^2? (M = Se, Te; X? X = ligand; E = lone-pair) with fourfold coordinated Se^II and Te^II, respectively. The complex anions [Se(i-mnt)₂E₂]^2? as well as [Te(i-mnts)₂E₂]^2? show a trapezoide distortion with d(Se? S) = 2.276(5); 2.287(5); 2.803(5); 2.789(5) Å and d(Te? Se) = 2.611(2); 2.617(3); d(Te? S) = 2.889(5); 2.935(4) Å. In III there are centrosymmetric complex anions [Te(i-mns)₂E₂]^2? with nearly identical Te? Se-bond-lengths: 2.674(3) and 2.692(2) Å. These Te? Se bonds are elongated compared to usual Te? Se bonds.     

Accurate time-resolved laser spectroscopy on sputtered metal atoms

The delayed coincidence photon counting technique, employing a picosecond tunable dye laser as an excitation source, has been used for accurate determinations of radiative lifetimes of excited states. Excitation from meta-stable states of sputtered atoms was employed. We obtained for Cu: τ(3d ¹⁰ 4p ² P _1/2 = 7.27(0.06) ns, τ(3d ¹⁰ 4p ² P _3/2) = 7.17(0.06) ns and for Fe: τ(3d ⁷ 4p y ³ F ₂)= 9.06(0.16) ns, τ(3d ⁷ 4p y ³ F ₃) = 9.06(0.13) ns and τ(3d ⁷ 4p y ³ F ₄) = 9.11 (0.16) ns. Also, the ability of this technique to record quantum beats at frequencies up to 1 GHz is demonstrated.     

Zweikernige η5-pentamethylcyclopentadienyl-rhenium-komplexe mit einer chalkogenbrücke. Die molekülstruktur von [(η5-C5Me5)Re(CO)2]2(μ-Se)

We report the synthesis and characterisation of binuclear η⁵-pentamethylcyclopentadienylrhenium complexes, [(η⁵-C₅Me₅)Re(CO)₂]₂(μ-E) (E = S (2), Se (3), Te (4)), containing a chalcogen bridge in addition to a ReRe bond. According to the X-ray structural analysis, 3 possesses approximately C₂ molecular symmetry; the C₅Me₅ ring ligands occupy trans positions with respect to the central Re₂Se unit [d(ReRe) 3.032(1) Å, ∢ ReSeRe 74.9(1)°]. As expected, the complexes of the now complete series [CpRe(CO)₂]₂(μ-E) (E = O (1), S (2), Se (3), Te (4)) show a high degree of similarity in their corresponding mass, IR, ¹H and ¹³C NMR spectra.     

Synthesis and complexation of a new facultative tridentate S2Te donor ligand MeS(CH2)3Te(CH2)3SMe: crystal structures of [Rh(Cp*)(S2Te)][PF6]2 and [PtCl(S2Te)]PF6

The syntheses and spectroscopic characterisation of the new facultative tridentate tellurium containing ligands MeS(CH₂)₃Te(CH₂)₃SMe (S₂Te) and H₂N(CH₂)₃Te(CH₂)₃NH₂ are described. The complexes of the former, fac-[Mn(CO)₃(S₂Te)]CF₃SO₃, [Rh(Cp*)(S₂Te)][PF₆]₂, [MCl(S₂Te)]PF₆ (M=Pd or Pt), [Cu(S₂Te)]BF₄ and [Ag(S₂Te)]CF₃SO₃ have been prepared and characterised by analysis, IR, ¹H-, ¹³C{¹H}-, ¹²⁵Te- and ¹⁹⁵Pt-NMR spectroscopy and mass spectrometry. The X-ray crystal structures of [Rh(Cp*)(S₂Te)][PF₆]₂ and [PtCl(S₂Te)]PF₆ are described. The results are compared with those obtained from complexes of the related tridentates Te{(CH₂)₃TeR}₂, Se{(CH₂)₃SeMe}₂ and S{(CH₂)₃SR}₂.     

Ground- and excited stateg-factors of Ba+

We observed the Zeeman-splitting of the 6S _1/2-6P _1/2 resonance transition of Ba⁺ ions (493.4 nm) in a 6 T magnetic field. The ions were stored in a Penning quadrupole trap. From the splitting and the simultaneously measured cyclotron frequency of stored electrons we derived theg-factors of the 6S _1/2 and 6P _1/2 states. The results areg(6S _1/2)=2.00267(20) andg(6P _1/2)=0.66634(22).     

Improved lifetime measurements of the 3D3/2 and 3D5/2 metastable states of Ca II

The lifetimes of both metastable 3D-levels of Ca⁺ have been measured using the ion storage technique. Operation at UHV-conditions eliminated the earlier reported problems of collisional finestructure mixing between those states [1], which is inherent to measurements at buffergas background. The results of τ(D _3/2)=1113(45) ms and τ(D _5/2)=1054(61) ms improve our earlier result [1] by almost one order of magnitude and are in good agreement with recent theoretical calculations [3, 4, 5].     

The Reactions of Sulfur,Selenium and Tellurium with Fluorosulfuric Acid

Abstract

In fluorosulfuric acid, four different sulfur species: S₂ ⁺., S⁺., S(II+), S(IV+), 3 different selenium species: Se₂ ⁺., Se(II+), Se(IV+), and 3 different Tellurium species: Te₂ ²⁺, Te(II+) and Te(IV+) have been observed spectrophotometrically and electrochemically by varying the composition of the solvent from basic (non-oxidizing) medium (0.1M solution of NaSO₃F) to oxidizing media (0.5M solution of SO₃).     

Wavelength and lifetime data on intercombination transitions in the Si I isoelectronic sequence: Ni14+ and Cu15+

The 3s ²3p ^{2 3} P _{1, 2}–3s3p ^{3 5} S ₂ ⁰ transitions in Ni¹⁴⁺ and Cu¹⁵⁺ have been identified in beam-foil spectra. The wavelengths have been measured (41.700±0.01 nm/43.998±0.01 nm for Ni¹⁴⁺, 38.76±0.03 nm/41.02±0.02 nm for Cu¹⁵⁺) in delayed spectra. For the first time in this isoelectronic sequence the lifetime of the⁵ S ₂ ⁰ level has been determined (Ni: 33±5 ns, Cu: 22±3 ns). Experimental problems are discussed. The results are compared with theoretical data.     

Lifetime measurements of the 2p 3d 3 D 1, 2, 3 0 and 2p 3d 1 P 1 0 levels in NII by beam-foil-laser spectroscopy

Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d ³ D ₁ ⁰ )=0.209±0.007 ns, τ(2p 3d ³ D ₂ ⁰ )=0.219±0.007 ns, τ(2p 3d ³ D ₃ ⁰ )=0.217±0.005 ns, and τ(2p 3d ¹ P ₁ ⁰ )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.     

Laser excited S2 → S1 and S1 → S0 emission spectra and the S2 → Sn absorption spectrum of azulene in solution

We present the S₁ → S₀ fluorescence spectrum, between 740 and 940 nm, of azulene solutions (10^?3 M in methanol) excited with a Q-switched ruby laser. The nitrogen-laser excited S₂ → S₁ fluorescence spectrum, between 700 and 930 nm, is also reported. The transient S₁ → S_n spectrum between 500 and 650 nm was studied, using synchronous nitrogen laser and dye laser excitation. The S₅ (¹B₁(3)) state of azulene was found to be located at 45500 cm^?1 and the cross section σ₂₅ of the transient absorption S₂ → S₅ is estimated to be 3 × 10^?18 cm²/molecule.     

An improved laser vaporization cluster source and time-of-flight mass spectrometer

The radiative lifetimes of the 7p ² P _{3/2, 1/2} states of silver and the hyperfine structure of the 7p ² P _3/2 state have been measured using pulsed laser excitation and direct observation of the induced fluorescence light decay. In order to excite this doublet, VUV radiation at 185 nm was applied, as generated by frequency tripling and anti-Stokes Raman shifting of the output of a Nd: YAG laser pumped dye laser. The lifetimes were found to be τ=255(20) ns and τ=285(25) ns for theJ=3/2 state andJ=1/2 state, respectively. The hyperfine structure of the 7p ² P _3/2 state was measured by the quantum beat method. The magnetic dipole interaction constant for the¹⁰⁷Ag isotope was found to bea=?4.5(2) MHZ.     

PHOTOPHYSICAL AND PHOTOSENSITIZING PROPERTIES OF BENZOPORPHYRIN DERIVATIVE MONOACID RING A (BPD-MA)*

The photophysical properties of benzoporphyrin derivative monoacid ring A (BPD-MA), a second-generation photosensitizer currently in phase II clinical trials, were investigated in homogeneous solution. Absorption, fluorescence, triplet-state, singlet oxygen (O₂(¹Δ_g)) sensitization studies and photobleaching experiments are reported. The ground state of this chlorin-type molecule shows a strong absorbance in the red (λ≈ 688 nm, ?≈ 33 000 M^?1 cm^?1 in organic solvents). For the singlet excited state the following data were determined in methanol: energy level, E_s= 42.1 kcal mol^?1, lifetime, Φ_f= 5.2 ns and fluorescence quantum yield, Φ_f= 0.05 in air-saturated solution. The triplet state of BPD-MA has a lifetime, τ_f >. 25 ns, an energy level, E_T= 26.9 kcal mol^?1 and the molar absorption coefficient is ?_T= 26 650 M^?1 cm^?1 at 720 nm. A dramatic effect of oxygen on the fluorescence (φ_f) and intersystem crossing (φ_T) quantum yields has been observed. The BPD-MA presents rather high triplet (φ_T= 0.68 under N₂-saturated conditions) and singlet oxygen (φ_Δ= 0.78) quantum yields. On the other hand, the presence of oxygen does not significantly modify the photobleaching of this photostable compound, the photodegradation quantum yield (φ_Pb) of which was found to be on the order of 5 × 10^?5 in organic solvents.     

Synthese und Kristallstrukturen von (NEt4)2[TeS3], (NEt4)2[Te(S5)(S7)] und (NEt4)4[Te(S5)2][Te(S7)2]

Synthesis and Crystal Structures of (NEt₄)₂[TeS₃], (NEt₄)₂[Te(S₅)(S₇)], and (NEt₄)₄[Te(S₅)₂][Te(S₇)₂] (NEt₄)₂[TeS₃] was obtained by the reaction of NEt₄Cl, Na₂S₄ and tellurium in acetonitrile. It reacts with sulfur, yielding (NEt₄)₂[Te(S₅)(S₇)], which is transformed to (NEt₄)₄[Te(S₅)₂][Te(S₇)₂] by recrystallization from hot acetonitrile. According to the X-ray structure analysis, crystals of (NEt₄)₂[TeS₃] are monoclinic (space group P2₁/c) and form twins with the twinning plane (001); they contain pyramidal TeS₃^2– ions. (NEt₄)₂[Te(S₅)(S₇)] forms triclinic twins (space group P1) with the twinning plane (010). In the [Te(S₅)(S₇)]^2– ion an S₅ and an S₇ atom group are bonded in a chelate manner to the tellurium atom, which has square coordination. (NEt₄)₄[Te(S₅)₂][Te(S₇)₂] (monoclinic, space group P2₁/c) contains two kinds of anions, the known [Te(S₅)₂]^2– and the new [Te(S₇)₂]^2– ion which has two S₇ chelating groups.     

Über Chalkogenolate. 198. Untersuchungen über Polythiocuprate (I) [Cu(Sx)]− 2. Hydrazinium- und Ethylendiammoniumpolythiocuprate(I)

On Chalcogenolates. 198. Studies on Polythiocuprates(I) [Cu(S_x)]^?. 2. Hydrazinium and Ethylenediammonium Polythiocuprates(I) The red polythiocuprates(I) 1–5 (formulae see ?Inhaltsübersicht”?) have been prepared by reaction of hydrazinium or ethylenediammonium polysulfides with copper(II) salts, dissolved in water, under variable conditions. Their properties are described. In aqueous alkaline media 1–5 decompose into CuS and S; in the presence of carbon disulfide CuS, S_x^2?, and CS₃^2? besides CS₄^2? and S₂CO^2? are formed. The existence of the discreet ion [Cu₂CS₇]^2?, described in literature, was not confirmed. The polythiocuprates(I) 1–5 , dissolved im dimethylformamide, decompose via the radical anion S₃^?. The decomposition of S₃^? has been studied kinetically by means of compound 5 . The half-life of decay of S₃^? is τ_1/2 = 71.5 h at 20°C. The pentathiocuprate(I) 3 reacts with n-butyl chloride to produce the substituted sulfanes (C₄H₉)₂S_x′ where x = 1, 2 and 3.     

Stabilization of Mo6S8 by halogens; new superconducting compounds: Mo6S6Br2, Mo6S6I2

We present a study of the properties of the series Mo₆X_8?xY_x (X = S, Se, Te; Y = Br, I) having the hexagonal rhombohedral structure of the PbMo₆S₈ type. For X = S we have found two new superconducting compounds Mo₆S₆Br₂ and Mo₆S₆I₂, having critical temperatures of 13.8 and 14.0°K, respectively. We further find that Mo₆Te₈ becomes superconducting (T_c ≈ 2.6°K) upon substitution of Te by small quantities of iodine, and that in the case of Mo₆Se₈ substitution of a Se atom by a halogen, raises T_c up to about 7.6°K.     

Dimeric and trimeric diorganosilicon chalcogenides (PhRSiE)2,3 (E = S, Se, Te; R = Ph, Me)

Ph₂SiCl₂ and PhMeSiCl₂ react with Li₂E (E = S, Se, Te) under formation of trimeric diorganosilicon chalcogenides (PhRSiE)₃ (R = Ph: 1a-3a, R = Me: cis/trans-4a (E = S), cis/trans-5a (E = Se)). In case of E = S, Se dimeric four-membered ring compounds (PhRSiE)₂ (R = Ph: 1b-2b, R = Me: cis/trans-4b (E = S), cis/trans-5b (E = Se)) have been observed as by-products. 1a-5b have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ²⁹Si, ⁷⁷Se, ¹²⁵Te). Four- and six-membered ring compounds differ significantly in ²⁹Si and ⁷⁷Se chemical shifts as well as in the value of ¹J_SiSe.The molecular structures of 2a, 3a and trans-5a reported in this paper are the first examples of compounds with unfused six-membered rings Si₃E₃ (E = Se, Te). The Si₃E₃ rings adopt twisted boat conformations. The crystal structure of 3a reveals an intermolecular Te-Te contact of 3.858 Å which yields a dimerization in the solid state.