Strychnine : A fast physical quencher of singlet oxygen (1Δg)

Pulsed laser excitation of 2-acetonaphthone in aerated benzene, toluene, acetone, acetonitrile or ethanol results in formation of O₂(¹Δ_g), the infrared luminescence of which has been monitored by time-resolved emission spectroscopy. The rate constants for the quenching of this emission by the indole alkaloid strychnine in all five solvents have been determined and compared with the corresponding values for the well-known O₂ (¹Δ_g) quencher DABCO. Strychnine (1) is the fastest known tertiary amine quencher of this species via a process which is at least 99% physical in character.     

Thermal-energy charge transfer of Ar+ with H2O: Internal and kinetic energy of the product H2O+

The reaction of Ar⁺ with H₂O has been investigated at near-thermal energy. The product ions H₂O⁺ and ArH⁺ account for 90 and 10% of the total reaction rate, respectively. Kinetic energy measurements and emission spectroscopy of the H₂O⁺ product ions are reported. It is concluded that at least 60% of H₂O⁺ ions are in the X? state with ≈2.4 eV vibrational energy while up to 40% are in the à state with a mean vibrational energy of 1.4 eV; the à state vibrational distribution has been determined. It is shown that both H₂O⁺ states are populated via an energetically “non-resonant” charge transfer process.     

Influence of solvent on the yield of singlet oxygen upon the chloride ion-catalyzed decomposition of dimethyldioxirane

The excitation yield of the singlet molecular oxygen ¹Δ _g [φ(¹O₂)] in the reaction of the dimethyldioxirane with the chloride ion in benzene, acetone, methylene chloride, and acetonitrile solutions has been determined. The φ(¹O₂) value depends on the solvent nature and is in the range 50–84%. Correlation between the value of the singlet oxygen yield and the Kamlet-Taft parameter (α) characterizing the acidity of the solvent as a hydrogen bond donor has been established: the higher the α value, the higher the ¹O₂ yield.     

Solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate initiator: Kinetics of polymerization and activation parameters for the primary decomposition of the initiator

The kinetics of solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate (aliquat persulfate) at 60°C has been studied in t-butyl alcohol, N,N-dimethyl formamide, acetonitrile, dioxane, acetone, and methyl ethyl ketone. The rate of polymerization depends markedly on the solvent used. The initiator exponent is close to 0.5 in the first three solvents but larger than this value in the other three solvents. The overall activation energy of the polymerization has been determined in all the solvents. The rate constants and activation parameters for the primary decomposition of the initiator have been determined in the first three solvents where ideal polymerization conditions prevail. The activation parameters for the decomposition of AQ₂S₂O₈ in the organic solvents depend on the type of solvent. They are very different from those of the free S₂O^2?₈ ion in water. These differences have been explained taking into consideration the various ionic forms in which the initiator exists in the studied solvents using a previously postulated model of the activated state.     

Luminescent organotin complexes with the ligand benzil bis(benzoylhydrazone)

Three organotin complexes have been synthesised by reaction of the ligand benzil bis(benzoylhydrazone) LH₂ with SnR₂Cl₂ or SnR₃Cl (R = Me, Bu, Ph). In all the compounds the ligand is doubly deprotonated and behaves as N₂O₂ tetradentate chelate, leading to distorted octahedral arrangements with the ligand in the equatorial plane and the organic groups in the axial positions. The complexes have been fully characterised by spectroscopic techniques including ¹³C and ¹¹⁹Sn NMR in solution and in the solid state, which confirm that the structure found in the solid state is retained in chloroform solution, and two of them by single crystal X-ray diffraction. The luminescent properties of the ligand and its complexes have also been tested as well as the effect of pH, the addition of acetone and the ionic strength over the luminescence intensity.     

Static secondary ion mass spectrometry of organic plasma-deposited films created from stable isotope-labeled precursors. II. Mixtures of acetone and oxygen

A series of plasma-deposited films (PDFs), created by blending controlled ratios of acetone vapor and oxygen in the feed to the plasma reactor, were analyzed by static secondary ion mass spectrometry (SIMS). Examination of the quadrupole-based static SIMS fragmentation patterns of acetone–O₂ PDFs created from ¹³C-labeled acetone generally allowed the hydrocarbon secondary ions to be distinguished from oxygen-containing secondary ions. These results were compared with those obtained via high-mass resolution time-of-flight (TOF)-SIMS. The identified secondary ions were then assigned structural attributes, based on comparison of the static SIMS spectra of the acetone–O₂ PDFs with those of conventional hydrocarbon and oxygen-containing polymers. A preliminary investigation to unravel the mechanism of oxygen incorporation in the acetone–O₂ PDFs from the two plasma feed components was undertaken through the analysis of PDFs created from 1,2,3¹³C₃-acetone(¹⁶O) vapor and ¹⁸O₂ gas.     

Radiochemical neutron activation analysis for determination of Au,Ag, Pt and Pd in geological samples

A procedure for separation of Au, Ag, Pt, and Pd in geological samples has been developed. After irradiation, samples were fused with Na₂O₂ and silver was separated by filtering through a PbCl₂ filter in 4M nitric acid solution. Au, Pt and Pd were concentrated with rhodium and thiourea as rhodium sulfide and the separation process of these elements was carried out by a chromatographic method. Au, Pt and Pd were retained on a Dowex-1×8 anion column in 1M HCl. Pd was eluted from the column by using a mixture of 75% HCl acid-25% acetone. Au was eluted by using a mixture of 10% HCl-90% acetone. In the gold fraction, Pt was also determined through the photopeak of¹⁹⁹Au radionuclide (158 keV). The method was simple and rapid.     

Picosecond time-resolved spectroscopy and the intersystem crossing rates of anthrone and fluorenone

The rise time of the T_n ← T₁ absorption of anthrone in benzene is determined to be 70 ps. The mechanism of efficient intersystem crossing of anthrone has been discussed and is compared with that of benzophenene. The rise time of fluorenone has been found to be sensitive to solvent, changing from 140 ps in cyclohexane to 12 ns in acetone. This tendency is explained in terms of the change in the character of the lowest excited singlet state of fluorenone from ππ^* in acetone to nπ^* in cyclohexane.     

Excited states of gaseous ions. V. The predissociation of the h2o+ ion

The B?² state of H₂O⁺ is predissociated twice. First, by the ã⁴B₁ state, giving OH⁺ + H fragments via spinorbit coupling interaction. Secondly, by a²A state, giving H ⁺ OH fragments via spin-orbit coupling and Coriolis interactions. A vibrational analysis of the photoelectron band of the B? state of H₂O⁺ and D₂O⁺ is carried out. This provides the vibrational frequencies of the H₂O⁺, D₂O⁺ and HDO⁺ ions, as well as a vibrational assignment of the peaks. The H₂O⁺ ion in its B?²B₂ state is found to have a OH bond length of 1.12 A and a valence angie of 78°.In order to describe the unimolecular fragmentation process, a distinction is introduced between the totally symmetric, optically active vibrational modes, and the antisymmetric ones which are coupled to the continuum. The former are supplied with photon or electron impact energy, but only the latter are chemically efficient. The dynamics of the dissociation process depends therefore on the couplings among normal modes. This is studied in the framework of two models. In Model 1, it is assumed that, as a result of the anharmonicity of the potential energy surface, only even overtones of the antisymmetric vibration are excited by Fermi resonance. In Model II, excitation of the odd overtones is provided by vibronic coupling. Model II is in better agreement with experiment than Model I. Calculated and experimental results have been compared on the following points: isotopic shift on the appearance potential of OH⁺ and OD⁺ ions, shapes of the photoionization curves, fragmentation pattern with 21 eV photons, presence of a unimolecular metastable transition, production of O⁺ ions. All the vibrational levels situated above the dissociation asymptote are totally predissociated. Autoionization is shown in this case to contribute only to the formation of molecular H₂O⁺ ions, and not to that of the OH⁺ fragments. For 21 eV electrons, the contribution due to direct ionization is calculated to represent about 25% of the total cross section, the rest being due to autoionization.     

A further study of the near-thermoneutral reactions O2H+ + H2 ⇌ H3+ + O2

The forward and reverse rate coefficients for the reactions (1) O₂H⁺ + H2 ? H₃⁺ + O₂ and (2) O₂D⁺ + D₂ ? D₃⁺ + O₂ have been determined in a SIFT at 80 and 300 K, from which values of the enthalpy and entropy changes in the reactions have been obtained. The data indicate that the proton affinity of H₂ is greater than that of O₂ by 0.33 ± 0.04 kcal mole^?1; similary, the deuteron affinity of D₂ is 0.35 ± 0.04 kcal mole^?1 greater than that of O₂. The measurements of entropy changes confirm that O₂H⁺ has a triplet electronic ground state.     

Kinetics and mechanism of the highly efficient generation of singlet oxygen in dimethyldioxirane decomposition induced by the chloride ion

The decomposition of dimethyldioxirane induced by the chloride anion has been investigated by methods of infrared chemiluminescence and quantum chemistry. The reaction leads to efficient generation of singlet excited molecular oxygen ¹O₂ (the excitation yield in acetone is 61%). A mechanism of peroxide decomposition is proposed in which the key reactions are the addition of the chloride ion to an oxygen atom of dioxirane, resulting in dioxirane ring opening and the formation of the 2-chlorooxy-2-hydroxy propane alcoholate (k ₁), and the interaction of the latter with another dimethyldioxirane molecule. This interaction results either in the formation of an adduct, which further decomposes to evolve ¹O₂, and catalyst regeneration (k ₂) or in the formation of the 2-chloroxyisopropyl radical, which leads to the irreversible consumption of the chloride ion catalyst (k ₃). The decay kinetics of the infrared chemiluminescence of ¹O₂ has been studied in a wide range of reactant concentrations. The temperature dependence of the rate constant of the reaction of dimethyldioxirane with the chloride ion has been determined by a kinetic analysis of the mechanism proposed: log(² k ₁) = (11.1 ± 0.7) − (46 ± 4)/Θ, where Θ = 2.3RT kJ/mol. Estimation of the ratio of the rates of the reaction of the 2-chlorooxy-2-hydroxy propane alcoholate with dimethyldioxirane via two pathways (k ₃/k ₂) has demonstrated that the fraction of the process involving electron transfer does not exceed 1.5% under the experimental conditions examined. Nevertheless, the latter reaction, which withdraws the chloride ion from the catalytic cycle of dimethyldioxirane decomposition yielding singlet oxygen, has a marked effect on the overall kinetics of the process.     

The quenching of chlorine fluorescence in the gas phase

Laser induced fluorescence has been observed from the B³Π(O⁺_u) state of chlorine. Lifetimes have been measured from 19 to 208 Pa, but the radiative lifetime is too long to be extracted from the data. A rate coefficient of 3.2 × 10[su13] cm³ mol?1 s?1 was measured for quenching by Cl₂ or Ar, the removal process being collision induced predissociation of the ³Π(O⁺_u) state.     

Photogeneration of singlet molecular oxygen (1O2, 1Δ g ) using monomeric and aggregated forms of copper tetra-4-(morpholine-4-yl)-tetra-5-(2-naphthoxy)phthalocyanine in organic solvents

Luminescence and chemical acceptors methods were used to study the photosensitized formation of singlet molecular oxygen (¹O₂, ¹?? _g ) by monomer and aggregated forms of copper tetra-4-(morpholine-4-yl)-tetra-5-(2-naphthoxy)phthalocyanine in benzene, benzene-d ₆, acetone, DMF, and pyridine. The values of ¹O₂ quantum yield were determined. The effectiveness of the ¹O₂ photoproduction was shown to be reduced due mainly to the aggregation of the copper phthalocyanine molecules.     

Thermal Decomposition of Strontium Iron Citrate

The citrate precursor method has been used to synthesise ultrafine SrFe₁₂O¹⁹. The thermal decomposition of citrate precursor SrFe₁₂O₆ (C₆H₆O₇)₁₃ was investigated by TG, DTG and DTA techniques, gas and chemical analyses. The citrate precursor on decomposition in static air atmosphere yields pure and stoichiometric SrFe₁₂O₁₉. The decomposition consists of three major steps, the formation of acetone dicarboxylate complex occurs around 165°C. The citrate groups are completely destroyed in the temperature range 195–315°C resulting in the formation of complex carbonate with the evolution of acetone and CO₂ gas. The decomposition of carbonate results in the formation of ultrafine SrFe₁₂O₁₉ below 550°C with the evolution of CO₂ gas. The ultrafine particles are observed as platelet clusters having crystallite size 13 nm and surface area 76.4 m² g^?1. The citrate precursor and the decomposed products were characterised by IR, NMR, XRD, SEM and surface area measurements.     

The observation of predissociations in the oxygen molecular ion by low-energy electron impact

The kinetic energy distribution of the O⁺ ions formed by dissociative ionization of O₂ has been carefully examined in the range of 0.0 to 1.3 eV. In the peak at 600 meV fine structure is observed and interpreted by predissociation. The high energy side of the peak has been ascribed to the predissociation of the ²Δ_g, B²Σ^?_g and the C⁴Σ^?_u states of O⁺₂. The low energy side of the peak is presumably due to the predissociation of the b⁴Σ^?_g state or the ²Φ_u state of O⁺₂ or to autoionizing predissociation.     

Crossed beam study of He+-O2 charge transfer reactions in the collision energy range 0.5–200 eV

Energy spectra and angular distributions of the O⁺ and O ₂ ⁺ product ions resulting from the He⁺-O₂ charge transfer reaction have been measured in the collision energy range 0.5–200 eV using the crossed-beam method. The O ₂ ⁺ ions represent only a minor fraction of the reaction products (0.2–0.6% over the energy range measured). In the dissociative charge transfer reaction, four main processes are identified leading to O+O⁺ reaction products in different electronic states. Two different mechanisms can be distinguished, each being responsible for two of the observed processes:(i) a long-distance energy-resonant charge transfer process involving thec ⁴∑ _u ^? (v′=0) state of O ₂ ⁺ and(ii) a slightly exothermic charge transfer process via the (III)²∏ _u state of O ₂ ⁺ (with the exothermicity depending on the collision energy). Angle-integrated branching ratios and partial cross sections (in absolute units) have been determined. The branching ratios of the individual processes show a pronounced dependence on the collision energy. At low energies, the O⁺ product ions are preferentially formed in the² P ⁰ and² D ⁰ excited states. The angular distributions of the O⁺ product ions show an anisotropic behaviour indicating an orientation-dependent charge transfer probability in the He⁺ ?O₂ reaction.     

Tandem mass spectrometry studies of acetone and acetone/water cluster ions

Ion clusters were formed in a temperature-variable high-pressure ion source from neat acetone and acetone/water mixtures and subjected to tandem mass spectrometry studies-unimolecular and collisionally activated mass-analyzed ion kinetic energy spectroscopy. The predominance of water loss from H⁺(H₂0)(A) _l=3, where A = acetone, suggests that the solvation sphere around H₃O⁺ does not close at l = 3, contrary to the case of acetonitrile or dimethyl ether. The results may be interpreted in terms of suggested ion structures which involve isomerization enroute to dissociation. The virtual absence of H/D scrambling in the collisionally activated dissociation of H₃O⁺(DA)₃, DA =acetone-d ₆, and of D₃O⁺(A)₃ means that if enolization takes place, it is a rate-determining step in an irreversible isomerization. The stability of H⁺(H₂O)(A)₃ is a dominant factor in the observation of acetone loss from H⁺(H₂0)(A)₄.     

Synthesis,molecular and electronic structure of [ReCl2(N2COPh)(C4N2H4)(PPh3)2]

A new organodiazenido rhenium complex, [ReCl₂(N₂COPh)(C₄N₂H₄)(PPh₃)₂] has been obtained from the direct reaction of [ReCl₂(η²–N₂COPh–N′,O)(PPh₃)₂] with pyrazine in acetone. The complex has been characterized by spectroscopic methods and its structure determined using single-crystal X-ray diffraction techniques.     

Collisional deactivation of O2(1Σg+)

Relaxation rates for O₂(¹Σ_g⁺) by nonradiative pathways have been determined using the fast-flow technique. O₂(¹Σ_g⁺) is formed from O₂(¹Δ_g) by an energy pooling process. O₂(¹Δ_g) is generated by passing purified oxygen through a microwave discharge. Oxygen atoms are removed by distilling mercury vapor through the discharge zone. It has been observed that the wall loss rate for O₂(¹Σ_g⁺) decreases with increasing pressure of oxygen and thus appears to be diffusion controlled. Quenching rate constants for O₂, N₂, and He have been determined and found to be (1.5 ± 0.1) × 10⁴, (1.0 ± 0.05) × 10⁶ and (1.2 ± 0.1) × 10⁵ l./mol·sec, respectively.     

Kinetics of the uptake of SO2 on mineral oxides: Improved initial uptake coefficients at 298 K from pulsed Knudsen cell experiments

The uptake of SO₂ on γ‐Fe₂O₃, γ‐Al₂O₃, and Saharan dust has been studied at T = 298 K using a Knudsen cell reactor operated in a steady‐state as well as in a pulsed mode. The initial uptake coefficients determined in the steady‐state mode have been found to be affected by surface saturation as well as bulk diffusion of SO₂ resulting in an apparent dependence of the initial uptake coefficients on the sample mass of the mineral oxides. However, by operating the Knudsen cell in the pulsed mode with shorter response time, these effects could be suppressed. Initial uptake coefficients of γ_ini (Fe₂O₃) = (8.8 ± 0.4) × 10^?2, γ_ini (Al₂O₃) = (7.4 ± 0.9) × 10^?3, and γ_ini (Saharan dust) = (7.6 ± 0.5) × 10^?2 were derived. This suggests that Fe₂O₃ is an important component in determining the reactivity of mineral dusts. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 242–249, 2006