Weijun Zheng

Cobalt–benzene cluster anions: Mass spectrometry and negative ion photoelectron spectroscopy

(Cobalt)n(benzene)m− cluster anions, (n,m) were generated by laser vaporization and studied by both mass spectrometry and anion photoelectron spectroscopy. Our assignment of the photoelectron spectrum of the (1,2) cluster anion suggests that it possesses a sandwich structure with the cobalt atom located between two parallel benzene rings, that the ground state of this anion is a singlet, and that the ground state of its corresponding neutral is a doublet. The photoelectron spectra of cobalt-rich cluster anions of the form (n,1) are interpreted as cobalt metal cluster anions which have been solvent-stabilized by their interaction with, in each case, a single benzene molecule. The photoelectron spectra of the benzene-rich cluster anions, (2,3), (2,2), and (3,3), are tentatively interpreted as suggesting extended sandwich structures for these anion complexes.

Formation of Hydrogen, Oxygen, and Hydrogen Peroxide in Electron-irradiated Crystalline Water Ice

Water ice is abundant both astrophysically, for example, in molecular clouds, and in planetary systems. The Kuiper belt objects, many satellites of the outer solar system, the nuclei of comets, and some planetary rings are all known to be water-rich. Processing of water ice by energetic particles and ultraviolet photons plays an important role in astrochemistry. To explore the detailed nature of this processing, we have conducted a systematic laboratory study of the irradiation of crystalline water ice in an ultrahigh vacuum setup by energetic electrons holding a linear

Direct electrochemistry and electrocatalysis of hemoglobin immobilized in TiO2 nanotube films

Titanium oxide nanotubes (TiO(2)-NTs) synthesized by the hydrothermal method had been prepared as the co-immobilization matrix to incorporate hemoglobin (Hb) successfully. The nanostructures of TiO(2)-NTs were investigated by X-ray diffraction and high-resolution electron microscopy. The Hb immobilized in TiO(2)-NTs had a similar structure to the native of Hb and retained its near-native conformations as characterized by the UV-vis and FT-IR spectroscopy. A couple of quasi-reversible redox peaks with a formal potential of -0.34 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffered saline (PBS) were observed. The amperometric response of the immobilized Hb linearly to H(2)O(2) concentration ranged from 4 microM to 64 microM with a detection limit of 4.637 x 10(-6)M and the high stability of the immobilized Hb in TiO(2)-NTs constituted a promising platform for the development of biosensors.

Magic numbers in copper-doped aluminum cluster anions

Copper-doped aluminum cluster anions, CuAln− were generated in a laser vaporization source and examined via mass spectrometry (n=2–30) and anion photoelectron spectroscopy (n=2–15). The mass spectrum of the CuAln− series is dominated by CuAl13− with other magic numbers also appearing at n=6, 19, and 23. The electron affinity versus cluster size trend shows a peak at n=6 and a dip at n=13. These results are discussed in terms of the reordering of shell model energy levels and the enhanced stability of neutral CuAl13. Reordering, which is a consequence of the copper atom residing in the central region of these clusters, provides an anion-oriented electronic rationale for the observed magic numbers.

In search of theoretically predicted magic clusters: Lithium-doped aluminum cluster anions

Lithium-doped aluminum cluster anions, LiAln− were generated in a laser vaporization source and examined via mass spectrometry and anion photoelectron spectroscopy (n=3–15). The mass spectrum of the LiAln− series exhibits a local minimum in intensity at n=13. The electron affinity vs cluster size trend also shows a dip at n=13. Agreement is quite good between our measured electron affinity values and those calculated by Rao, Khanna, and Jena, suggesting that their predictions about the structure and bonding of LiAl13 and other clusters in this series are also largely valid.

Photoelectron spectroscopy of chromium-doped silicon cluster anions

The photoelectron spectra of chromium-doped silicon cluster anions, CrSi-(n), were measured over the size range, n=8-12. Their vertical detachment energies were measured to be 2.71, 2.88, 2.87, 2.95, and 3.18 eV, respectively. Our results support theoretical calculations by Khanna, Rao, and Jena [Phys. Rev. Lett. 89, 016803 (2002)] which found CrSi12 to be an enhanced stability (magic) cluster with its chromium atom encapsulated inside a silicon cage and with its magnetic moment completely quenched by the effects of the surrounding cage.

Structures and photoelectron spectroscopy of Cun(BO2)m− (n, m = 1, 2) clusters: Observation of hyperhalogen behavior

The electronic structures of CuBO(2)(-), Cu(BO(2))(2)(-), Cu(2)(BO(2))(-), and Cu(2)(BO(2))(2)(-) clusters were investigated using photoelectron spectroscopy. The measured vertical and adiabatic detachment energies of these clusters revealed unusual properties of Cu(BO(2))(2) cluster. With an electron affinity of 5.07 eV which is larger than that of its BO(2) superhalogen (4.46 eV) building-block, Cu(BO(2))(2) can be classified as a hyperhalogen. Density functional theory based calculations were carried out to identify the ground state geometries and study the electronic structures of these clusters. Cu(BO(2)) and Cu(BO(2))(2) clusters were found to form chainlike structures in both neutral and anionic forms. Cu(2)(BO(2)) and Cu(2)(BO(2))(2) clusters, on the other hand, preferred a chainlike structure in the anionic form but a closed ringlike structure in the neutral form. Equally important, substantial differences between adiabatic detachment energies and electron affinities were found, demonstrating that correct interpretation of the experimental photoelectron spectroscopy data requires theoretical support not only in determining the ground state geometry of neutral and anionic clusters, but also in identifying their low lying isomers.

Structures and magnetic properties of CrSin− (n = 3–12) clusters: Photoelectron spectroscopy and density functional calculations

Chromium-doped silicon clusters, CrSi(n)(-) (n = 3-12), were investigated with anion photoelectron spectroscopy and density functional theory calculations. The combination of experimental measurement and theoretical calculations reveals that the onset of endohedral structure in CrSi(n)(-) clusters occurs at n = 10 and the magnetic properties of the CrSi(n)(-) clusters are correlated to their geometric structures. The most stable isomers of CrSi(n)(-) from n = 3 to 9 have exohedral structures with magnetic moments of 3-5μ(B) while those of CrSi(10)(-), CrSi(11)(-), and CrSi(12)(-) have endohedral structures and magnetic moments of 1μ(B).

The stabilization of arginine's zwitterion by dipole-binding of an excess electron

The arginine parent anion was generated by a newly developed, infrared desorption-electron photoemission hybrid anion source. The photoelectron spectrum of the arginine anion was recorded and interpreted as being due to dipole binding of the excess electron. The results are consistent with calculations by Rak, Skurski, Simons, and Gutowski, who predicted the near degeneracy of arginines canonical and zwitterionic dipole bound anions. Since neutral arginines zwitterion is slightly less stable than its canonical form, this work also demonstrates the ability of an excess electron to stabilize a zwitterion, just as ions and solvent molecules are already known to do.

Formation of Hydroxylamine (NH2OH) in Electron-Irradiated Ammonia−Water Ices

We investigated chemical and physical processes in electron-irradiated ammonia-water ices at temperatures of 10 and 50 K. Chemically speaking, the formation of hydroxylamine (NH(2)OH) was observed in electron-irradiated ammonia-water ices. The synthesis of molecular hydrogen (H(2)), molecular nitrogen (N(2)), molecular oxygen (O(2)), hydrazine (N(2)H(4)), and hydrogen peroxide (H(2)O(2)), which was also monitored in previous irradiation of pure ammonia and water ices, was also evident. These newly formed species were trapped inside of the ices and were released into the gas phase during the warm-up phase of the sample after the irradiation. A quantitative analysis of the data showed that the production rates of the newly formed species at 10 K are higher compared to those at 50 K. Our studies also suggest that hydroxylamine is likely formed by the recombination of amino (NH(2)) with hydroxyl (OH) radicals inside of the ices. Considering the physical effects on the ice sampled during the irradiation, the experiments provided compelling evidence that the crystalline ammonia-water ice samples can be partially converted to amorphous ices during the electron irradiation; similar to the chemical processes, the irradiation-induced amorphization of the ices is faster at 10 K than that at 50 K--a finding which is similar to electron-irradiated crystalline water ices under identical conditions. However, the amorphization of water in water-ammonia ices was found to be faster than that in pure water ices at identical temperatures.