Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.     

Rapid spectroscopic confirmation of the presence of polystyrene in polymer particles of mixed composition

A technique for rapid determination of the presence of polystyrene in individual micron-diameter polymer particles of mixed composition is presented. This technique is based upon observation of visible emission from conjugated regions of the polymer backbone, generated photochemically, while the particle is held in an optical trap. Particle emission characteristics are dependent upon particle size and suspending solvent. Emission spectra are provided for single component polystyrene particles and mixed polymer particles containing poly(methyl methacrylate), poly(N-vinyl pyrrolidone), and polystyrene. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 999–1004, 1998     

Synthesis and characterization of polyimides with ether linkages

Thermoplastic and thermoset polyimides derived from 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and 4,4′-bis(4-aminophenoxy)-2,2′-dimethylbiphenyl (BAPD) were prepared and characterized. Their physical and thermal properties as well as the polyelectrolyte effect exhibited by BTDA–BAPP polyamic acids in NMP solution were discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2559–2567, 1999     

Microbial synthesis of silver nanoparticles by Bacillus sp.

A silver resistant Bacillus sp. was isolated through exposure of an aqueous AgNO₃ solution to the atmosphere. Silver nanoparticles were synthesized using these airborne bacteria (Bacillus sp.). Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analyses confirmed that silver nanoparticles of 5–15 nm in size were deposited in the periplasmic space of the bacterial cells; a preferable cell surface location for the easy recovery of biogenic nanoparticles.     

The interaction between adsorbed OH and O2 on TiO2 surfaces

Reduced TiO₂(110) surfaces usually have OH groups as a result of H₂O dissociation at oxygen vacancy defects. Because of excess electrons due to OH adsorption, OH/TiO₂ exhibit interesting properties favorable to further O₂ or H₂O adsorption. Both O₂ and H₂O can adsorb and easily diffuse on the OH/TiO₂ surface; such behavior plays a significant role in photocatalysis, heterogeneous catalysis, electronic devices and sensors. Indeed, the processes of H₂O dissociation, O₂ and H₂O diffusion on such TiO₂ surfaces, in the presence of OH groups, are important issues in their own right. Herein, the most recent experimental and theoretical progresses in understanding the interactions between adsorbed OH groups and O₂, or H₂O, over TiO₂(110) surfaces and their implications will be reviewed.     

The lowest 2A' excited state of the water-hydroxyl complex

Vertical and adiabatic excitation energies of the lowest (2)A(') excited state in the water-hydroxyl complex have been determined using coupled cluster, multireference configuration interaction, multireference perturbation theory, and density-functional methods. A significant redshift of about 0.4 eV in the vertical excitation energy of the complex compared to that of the hydroxyl radical monomer is found with the coupled cluster calculations validating previous results. Electronic excitation leads to a structure with near-equal sharing of the hydroxyl hydrogen by both oxygen atoms and a concomitantly large redshift of the adiabatic excitation energy of approximately 1 eV relative to the vertical excitation energy. The combination of redshifts ensures that the electronic transition in the complex lies well outside the equivalent excitation in the hydroxyl radical monomer. The complex is approximately five times more strongly bound in the excited state than in the ground state.     

Protonated 2-methyl-1,2-epoxypropane: a challenging problem for density functional theory

Protonated epoxides feature prominently in organic chemistry as reactive intermediates. Herein, we describe 10 protonated epoxides using B3LYP, MP2, and CCSD/6-311++G calculations. Relative to CCSD, B3LYP consistently overestimates the C2-O bond length. Protonated 2-methyl-1,2-epoxypropane is the most problematic species studied, where B3LYP overestimates the C2-O bond length by 0.191 angstroms. Seventeen other density functional methods were applied to this protonated epoxide; on average, they overestimated the CCSD bond length by 0.2 angstroms. We present a range of data that suggest the difficulty for DFT methods in modeling the structure of the titled protonated epoxide lies in the extremely weak C2-O bond, which is reflected in the highly asymmetric charge distribution between the two ring carbons. Protonated epoxides featuring more symmetrical charge distribution and cyclic homologues featuring less ring strain are treated with greater accuracy by B3LYP. Finally, MP2 performed very well against CCSD, deviating in the C2-O bond length at most by 0.009 angstroms; it is, therefore, recommended when computational resources prove insufficient for coupled cluster methods.