Haiyan Fan

Absolute Photoionization Cross-Section of the Methyl Radical†

The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; sigma(CH3)(10.2 eV) = (5.7 +/- 0.9) x 10(-18) cm(2) and sigma(CH3)(11.0 eV) = (6.0 +/- 2.0) x 10(-18) cm(2). The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 +/- 2.0) x 10(-18) cm(2) at 10.460 eV, (5.5 +/- 2.0) x 10(-18) cm(2) at 10.466 eV, and (4.9 +/- 2.0) x 10(-18) cm(2) at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry.

Spectrophotometric determination of palladium after solid-liquid extraction with 1-(2-pyridylazo)-2-naphthol at 90°C

Abstract An effective spectrophotometric determination of palladium with 1-(2-pyridylazo)-2-naphthol (PAN) using molten naphthalene as a diluent has been studied. A green complex of palladium with PAN is formed at 90°C. In the range of pH 1.5–7.5, the complex is quantitatively extracted into molten naphthalene. The organic phase is anhydrously dissolved in CHCl3 to be determined spectrophotometrically at 678 nm against the reagent blank. Beers law is obeyed over the concentration range of 0.5–10 ppm. The molar absorptivity and Sandells sensitivity are 1.2 × 104 l mol−1 cm−1 and 0.0070 mg cm−2, respectively. The optimum conditions for determination are obtained. The interferences of various ions are observed in detail. The method has been applied to the determination of palladium in synthetic samples.

Photoionization of hot radicals: C2H5,n-C3H7, and i-C3H7

The combination of ion-imaging and vacuum-ultraviolet (vuv) single-photon ionization is used to study the internal energy dependence of the relative photoionization yields of the C(2)H(5),n-C(3)H(7), and i-C(3)H(7) radicals following the 266 nm photodissociation of the corresponding alkyl iodides. The comparison of the ion images obtained by vuv photoionization of the radical with those obtained by two-photon-resonant, three-photon ionization of the complementary I (2)P(32) and I*(2)P(12) atoms allows the extraction of the internal energy dependence of the cross sections. Factors influencing the appearance of the ion images in the different detection channels are discussed, including the secondary fragmentation of the neutral radicals, Franck-Condon factors for the photoionization process, and the unimolecular fragmentation of the parent photoions.

Thermodynamic investigations of aqueous-molten paraffin wax liquid-liquid extractions and synergistic extractions of some trivalent rare earth elements.

In this paper, liquid-liquid extraction behaviour of RE(III) (RE = La, Sm, E, Yb) by the use of 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (PMBP) in liquid paraffin with cersin has been investigated at 343.2 K. Under some conditions, the synergistic extraction behaviour with PMBP and Phen has also been studied. The slope analysis method shows that the compositions of the extracted species are REA(3) and REA(3)B. pH(1 2 ) values were also obtained. Equilibrium extraction constants and thermodynamic parameters were calculated. The results showed that increasing temperature is favourable to extraction of heavy rare earth ions with PMBP and more favourable to synergistic extraction with PMBP and Phen. Synergistic extraction can be carried out at lower pH.

Halogen Bonding in Iodo-perfluoroalkane/Pyridine Mixtures

Mole fraction and temperature studies of halogen bonding between 1-iodo-perfluorobutane, 1-iodo-perfluorohexane, or 2-iodo-perfluoropropane and pyridine were performed using noisy light-based coherent anti-Stokes Raman scattering (I((2)) CARS) spectroscopy. The ring breathing mode of pyridine both is highly sensitive to halogen bonding and provides a strong I((2)) CARS signal. As the lone pair electrons from the pyridinyl nitrogen interact with the sigma-hole on the iodine from the iodo-perfluoroalkane, the ring breathing mode of pyridine blue-shifts proportionately with the strength of the interaction. The measured blue shift for halogen bonding of pyridine and all three iodo-perfluoroalkanes is comparable to that for hydrogen bonding between pyridine and water. 2-Iodo-perfluoropropane displays thermodynamic behavior that is different from that of the 1-iodo-perfluoroalkanes, which suggests a fundamental difference at the molecular level. A potential explanation of this difference is offered and discussed.

One-step synthesis of carbon nanodots for sensitive detection of cephalexin

Blue photoluminescence water soluble carbon dots with an average size of 1.5 nm were synthesized by hydrothermal treatment of fresh potato at 200 °C for 5 h without adding any other reagents. XRD and TEM illustrated the poor crystalline nature and narrow distribution of these spherical carbon dots. The functional groups were confirmed by FTIR studies. Thus bio-based photoluminescence carbon dots were applied to the detection of cephalexin. The sensing probe exhibits many advantages, such as wide linear response range, high sensitivity and short response time with a detection limit as low as 0.311 μM.

A hybrid antioxidizing and antibacterial material based on Ag–La2O3 nanocomposites

The Ag-La2O3 hybrid nanoparticles were prepared by loading Ag nanoparticles on the surface of the La2O3 nanorods. The synthesis was a one-step process where sodium borohydride was used as a reducing agent to convert silver ions into silver nanoparticles, which were further deposited on the La2O3 nanorods. Moreover, they were found evenly dispersed upon the surface of La2O3 supports. The as-prepared Ag-La2O3 nanocomposites showed anti-oxidizing and significant antibacterial effect in vitro. Using the results from transmission electron microscope (TEM), the plausible mechanism was also proposed to explain the inhibition of bacterial growth. The present strategy can be potentially extended to develop drug-labels and other antibacterial agents.

Unraveling the Ã1B1 ← X̃1A1 Spectrum of CCl2: The Renner−Teller Effect, Barrier to Linearity, and Vibrational Analysis Using an Effective Polyad Hamiltonian

We report studies aimed at unraveling the complicated structure of the CCl 2 A (1)B 1 <-- X (1)A 1 system. We have remeasured the fluorescence excitation spectrum from approximately 17,500 to 24,000 cm (-1) and report the term energies and A rotational constants of many new bands for both major isotopologues (C (35)Cl 2, C (35)Cl (37)Cl). We fit the observed term energies to a polyad effective Hamiltonian model and demonstrate that a single resonance term accounts for much of the observed mixing, which begins approximately 1300 cm (-1) above the vibrationless level of the A (1)B 1 state. The derived A (1)B 1 vibrational parameters are in excellent agreement with ab initio predictions, and the mixing coefficients deduced from the polyad model fit are in close agreement with those derived from direct fits of single vibronic level (SVL) emission intensities. The approach to linearity and thus the Renner-Teller (RT) intersection is probed through the energy dependence of the A rotational constant and fluorescence lifetime measurements, which indicate a barrier height above the vibrationless level of the X (1)A 1 state of approximately 23,000-23,500 cm (-1), in excellent agreement with ab initio theory.

The stability of allyl radicals following the photodissociation of allyl iodide at 193 nm

The photodissociation of allyl iodide (C3H5I) at 193 nm was investigated by using a combination of vacuum-ultraviolet photoionization of the allyl radical, resonant multiphoton ionization of the iodine atoms, and velocity map imaging. The data provide insight into the primary C-I bond fission process and into the dissociative ionization of the allyl radical to produce C3H3+. The experimental results are consistent with the earlier results of Szpunar et al. [J. Chem. Phys. 119, 5078 (2003)], in that some allyl radicals with internal energies higher than the secondary dissociation barrier are found to be stable. This stability results from the partitioning of available energy between the rotational and vibrational degrees of freedom of the radical, the effects of a centrifugal barrier along the reaction coordinate, and the effects of the kinetic shift in the secondary dissociation of the allyl radical. The present results suggest that the primary dissociation of allyl iodide to allyl radicals plus I*(2P(1/2)) is more important than previously suspected.

Near-threshold photoionization of hot isopropyl radicals.

A combination of ion imaging and vacuum ultraviolet, single-photon ionization is used to study the internal energy dependence of the photoionization cross section of isopropyl radicals produced by the 266 nm photodissociation of isopropyl iodide. The isopropyl radicals so produced have internal energies of approximately 0.3-2.0 eV. Images recorded for photoionization energies from just below the adiabatic ionization threshold at 7.37+/-0.02 and 8.04 eV are essentially identical both to each other and to that recorded at 9.67 eV. These results imply that the photoionization cross section is only weakly dependent on internal energy. Several factors contributing to this observation are discussed, as are the implications for the photoionization of other systems with significant internal excitation.