Biomedical subjects

Joshua T Maze

Publications and source records attributed to Joshua T Maze.

3 recordsLinked to original sources

PubMed2006

Negative droplets from positive electrospray.

Image charge detection has been used to measure the charge and velocity of individual electrosprayed water droplets. With a positive bias on the electrospray needle the majority of the droplets are, as expected, positively charged. However, a small fraction, surprisingly, carry a negative charge. Plausible explanations for the presence of the negatively charged droplets are discussed. In particular, we consider the possibility of the negatively charged droplets resulting from a bipolar fission process where the incorporation of a small negatively charged droplet between two larger positively charged progeny lowers the energy barrier for symmetric fission.

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PubMed2006

Reactivity of small Mo(x)Oy- clusters toward methane and ethane.

The reactions of Mo2Oy- suboxide clusters with both methane and ethane have been studied with a combination of mass spectrometry, anion photoelectron spectroscopy, and density functional theory calculations. Reactions were carried out under "gentle" and "violent" conditions. For methane, a number of products appeared under the gentler source conditions that were more logically attributed to dissociation of Mo2Oy- clusters upon reacting with methane to form MoCH2-, Mo(O)CH2-, and HMo(O2)CH3-. With ethane, products observed under the same gentle conditions were Mo(O)C2H2-, Mo(O)C2H4-, Mo(O2)C2H4-, and Mo(O2)(C2H5)2-. As expected, more products were observed when the reactions were carried out under violent conditions. The photoelectron spectra obtained for these species were compared to calculated adiabatic and vertical electron affinities and vibrational frequencies, leading to definitive structural assignments for several of the products.

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PubMed2005

Structures of Mo2Oy- and Mo2Oy (y=2, 3, and 4) studied by anion photoelectron spectroscopy and density functional theory calculations.

The competitive structural isomers of the Mo(2)O(y) (-)Mo(2)O(y) (y=2, 3, and 4) clusters are investigated using a combination of anion photoelectron (PE) spectroscopy and density functional theory calculations. The PE spectrum and calculations for MoO(3) (-)MoO(3) are also presented to show the level of agreement to be expected between the spectra and calculations. For MoO(3) (-) and MoO(3), the calculations predict symmetric C(3v) structures, an adiabatic electron affinity of 3.34 eV, which is above the observed value 3.17(2) eV. However, there is good agreement between observed and calculated vibrational frequencies and band profiles. The PE spectra of Mo(2)O(2) (-) and Mo(2)O(3) (-) are broad and congested, with partially resolved vibrational structure on the lowest energy bands observed in the spectra. The electron affinities (EA(a)s) of the corresponding clusters are 2.24(2) and 2.33(7) eV, respectively. Based on the calculations, the most stable structure of Mo(2)O(2) (-) is Y shaped, with the two Mo atoms directly bonded. Assignment of the Mo(2)O(3) (-) spectrum is less definitive, but a O-Mo-O-Mo-O structure is more consistent with overall electronic structure observed in the spectrum. The PE spectrum of Mo(2)O(4) (-) shows cleanly resolved vibrational structure and electronic bands, and the EA of the corresponding Mo(2)O(4) is determined to be 2.13(4) eV. The structure most consistent with the observed spectrum has two oxygen bridge bonds between the Mo atoms.

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