James F. Garvey

Generation of C59O− via collision induced dissociation of oxy-fullerene anions

Abstract We present an investigation of the anions observed during chemical ionization of C 60 in the presence of nitric oxide. Within the source of a triple quadrupole mass spectrometer, we initially generate a series of C 60 O 1−4 − anions. We observe that the C 60 O 2−4 − ions have a novel collision induced dissociation pattern producing C 59 O − and C 58 O 2 − . We speculate on a possible mechanism for the formation of these oxy-fullerene anions.

Argon mediated electron impact ionization of Arn(CH3OH)m heteroclusters

In this paper we have contrasted electron impact cluster mass spectra of a methanol/argon expansion with a methanol/helium expansion and have measured appearance potentials for several of the prominent ions in each case. We have observed a number of ionic species in the argon expansion (i.e., CHxO+ where x=0–4) which are not observed in the helium expansion. Appearance potentials for these species fall in the region 11.3–11.8 eV indicating that the threshold ionization of Arn(CH3OH)m heteroclusters is mediated by the Ar 4s excited states (3P2,0;11.55 and 11.72 eV). This represents the first time that intracluster Penning ionization has been positively identified using electron impact measurements.

Observation of ‘‘magic numbers’’ in the population distributions of the (NH3)n−1NH+2 and (NH3)nH+2 cluster ions: Implications for cluster ion structures

Abstract : We present the relative yields of the cluster ions, (NH3)n-1NH2+ and (NH3)nH2+, produced by electron impact ionization of a supersonic molecular beam of neutral ammonia clusters, as functions of cluster ion size, neutral beam stagnation temperature, and electron impact energy. Our observation of a magic number at n = 7 in the distribution of (NH3)n-1NH2+ cluster ions is interpreted in terms of an intracluster bimolecular association reaction between a nascent NH2+ daughter ion and an adjacent NH3 solvent molecule, giving rise to a protonated hydrazine product ion. Our observation of magic numbers at n = 5 and n = 8 in the (NH3)NH2+ cluster ion distribution is consistent with the production of the N2H8+ Rydberg radical cation via an intracluster ion molecule reaction. The dependence of the yields of these solvated Rydberg radical cations on the stagnation temperature of the neutral molecular beam supports the notion that extensive solvation destabilizes these cluster ions. Amines, Hydrogen, Clusters.

Ion-molecule chemistry within doubly charged ammonia clusters

Abstract We present the observation of “intramolecular” ion-molecule reactions within doubly charged clusters produced via electron impact ionization of neat beams of ammonia molecules. The fragmentation pattern strongly suggests that reactions occurring within these doubly charged clusters are similar to those observed for singly charged ammonia clusters. This behavior implies that these cluster ions consist of two separate, singly charged ammonia cations which act separately within the bulk neutral cluster. That is, either one, both, or neither of the ammonia cations may react with the neutrals solvating them within the doubly charged cluster.

Characterization of copper iodide thin films fabricated via laser‐assisted molecular‐beam deposition

The technique of laser‐assisted molecular‐beam deposition (LAMBD) has been used to fabricate a molecular film by reaction in a molecular beam. Molecular iodine vapor entrained into a stream of helium carrier gas was introduced via a supersonic expansion into the plasma plume of laser‐evaporated copper to produce copper iodide. Films were deposited on substrates that were situated about 3 cm downstream on the path of the molecular beam. The surface morphology of films depends greatly on the fluence of the incident laser beam and expansion conditions. Films grown at low laser powers show small surface inhomogeneities in their electron micrographs compared to the films that were grown at higher laser powers. Copper in the LAMBD films is found to be mainly in the Cu+1 state as characterized by electron spectroscopy for chemical analysis. A comparison of the surface and structural properties of LAMBD films with that of a vacuum‐evaporated film suggests that both films have similar lattice structures and compos...

Fabrication of a thin film of an inorganic:organic composite via laser assisted molecular beam deposition

Thin films of a hybrid organic:inorganic [silica: N‐4‐(4‐nitrophenyl)‐(s)‐prolinol] composite were fabricated by mixing the constituents in the gas phase via the technique of laser assisted molecular beam deposition. UV visible and infrared spectra indicate that the organic chromophore is trapped within the silica matrix without degradation. This approach will enable the fabrication of thin films of a variety of hybrid organic: inorganic composite materials which would otherwise be difficult to fabricate.

The nature of copper in thin films of copper iodide grown by laser-assisted molecular beam deposition : comparative ESCA and EDXS studies

Thin molecular films of copper iodide have been grown by direct chemical reaction within a molecular beam using laser-assisted molecular beam deposition. Molecular iodine vapour entrained in a helium carrier gas stream was supersonically expanded into the laser-ablated plasma plume of vaporized copper, producing copper iodide. Films of this material were grown on substrates situated in the path of this molecular beam. The oxidation state of copper and the chemical composition of these films were studied by electron spectroscopy for chemical analysis and energy-dispersive X-ray spectroscopy, and, the results were compared with those of a high-purity Cul powder. The binding energy of the Cu 2p3/2 photoelectron line and the kinetic energy of the X-ray-induced Cu L3M4.5M4.5 Auger line are determined to be the same for both samples. The surface morphology and extent of surface inhomogeneities in copper iodide films were found to be largely dependent on the fluence of the incident laser and the expansion conditions. Secondary electron images of these films indicate clustering of copper iodide on the surface of the films during film growth. The copper in these films is found to be in the Cu+ ionization state.

A reactive laser ablation source for the production of thin films

A discription of a thin film deposition source which is based upon the “Smalley metal cluster source” is presented. Our laser assisted molecular beam deposition source incorporates four major innovations: (1) placing the source so it sits external to the deposition chamber, (2) positioning the ablation target at an angle greater than 90° with respect to the laser entrance window, (3) placing the laser entrance window/lens further from the ablation target, and (4) the addition of a second optical window for laser alignment and in situ spectral analysis of the laser ablation plume. Novel molecules can be generated in this source through use of a reactive carrier gas. For example, employing a Ti target rod and O2 carrier gas; flat, uniform micron thick thin films of TiO2 can be easily generated.

Transition states for H atom transfer reactions in the CH 2CH2OH radical: The effect of a water molecule

H atom transfer reactions in the 2-hydroxyethyl radical (CH2CH2OH), formed by addition of an OH radical to ethylene, have been computationally evaluated both in the gas-phase and in the presence of a single water molecule, and the corresponding transition state (TS) structures determined and discussed. The considered isomerization reactions of CH2CH2OH include a [1,3] hydrogen shift to form CH3CH2O (reaction (1)) and a [1,2] hydrogen shift to form CH3CHOH (reaction (2)). The presence of a single water molecule in two-step processes was found to significantly reduce the energy barrier for these rearrangements by providing alternative mechanisms that avoid the strained TSs found in the unimolecular gas phase and in the single-step water-assisted synchronous reactions. In addition, the effect of one water molecule in the single-step [1,3] hydrogen rearrangement of vinyl alcohol (reaction (3)), the product of one hydrogen atom abstraction from CH2CH2OH, has also been considered and discussed. Unlike reactions (1) and (2), where the water-assisted single-step processes yielded energy barriers higher than the gas-phase reactions, the TS system for reaction (3) has an energy barrier well below the energy barrier for the single-step gas-phase mechanism. While the computed activation energies for the lower activation energy reaction paths are still significant and there may be other reactions for the CH2CH2OH radical that are more energetically favorable, this study suggests that gas-phase chemistry can be significantly altered in the unique solvated environment of a gas-phase cluster.

Cationic Polymerization within Clusters Composed of Unsaturated Molecules

Abstract Electron impact ionization of large neutral clusters composed of simple olefinic molecules (ethene, 1,1-difluoroethene and propene) display highly anomalous ion intensity distributions. These cluster ion distributions typically exhibit a magic number at n = 4, for cluster ions of the type {M}+, where M is an olefinic molecule. The explanation which best explains this observation is that these small ‘cluster’ ions are in actuality covalently bound molecular ions formed by sequential ion-molecule association (polymerization) reactions which have occurred within the cluster ion. This size dependent cluster chemistry is accounted for by kinetic bottlenecks which occur in the ionic chain growth reactions and which terminate with the formation of cyclic molecular ions (i.e. cyclopentanes and cyclohexanes ions). The condensed phase counterparts of these intracluster reactions are the free cationic polymerization reactions initiated by radiolysis of bulk samples of the olefins. In addition to reviewing o...