Denise C. Parent

Oxidation reactions and photochemistry of aluminum cluster anions (Al3− to Al23−)

Abstract Reactions of mass-selected Aln− (n=3–23) with O2 produce AlO2−, AlO−, and electron detachment (n≤8); or Aln−4− (n=8–12, 14–22) and sequential dissociation products. All clusters except Al13− absorb at 1064 nm, losing one atom or electron. Several clusters require sequential absorption of two 1064 nm photons to dissociate. Single-photon excitation of Al16− and Al18− retards their oxidation reactions by factors of 2.5±1.0 and 5.0±2.0, respectively. Radiative relaxation of Al16− proceeds with a rate constant of 0.47±0.10 s−1, measured by the return to thermal reaction behavior.

Characterization of cluster ions produced by the sputtering or direct laser vaporization of group 13 metal (Al, Ga, and In) oxides

The stabilities and reactivities of cluster ions generated from the fast‐atom bombardment (FAB) or the direct laser vaporization (DLV) of the Group 13 metal oxides (Al2O3, Ga2O3, and In2O3) were examined by mass spectrometry. The nascent cluster ion distributions, fragmentations, and reactions were studied. The observed patterns of stability and reactivity were compared with the structures and heats of formation calculated from theoretical studies of aluminum oxide cluster ions using MNDO, Xα, and Born–Mayer pair potentials. The method of production of the metal oxide cluster ions, whether by FAB, DLV, or through the reaction of sputtered bare metal cluster ions with oxygen, had little influence on the abundance distribution observed. In agreement with the known M–O binding energies, a trend of increasing cluster oxidation state was observed in the abundance distributions of the cluster ions for decreasing metal atom z value. Dissociation of the oxide cluster ions occurred through the loss of particularly...

Formation of silicon carbide cluster cations and their reaction with acetylene. Unusual behavior of the disilicon carbide ions

Abstract Formation of silicon carbide cation clusters (SiC+y, y = 0–12 and Si2C+y, y = 0–11) by direct laser vaporization is reported. The reactions with acetylene were studied in a Fourier transform ion cyclotron resonance mass spectrometer, and product branching ratios and rate constants are tabulated. Monosilicon carbide cations react similarly to pure carbon clusters to add C2H at a rate approximately half Langevin. These results are interpreted as favoring a linear SiC+y structure possessing a reactive carbene site. Disilicon carbide cations exhibit unusual non-linear kinetics: at first reacting slowly to add CH2, followed by an increase in reactivity and adduct formation. Carbon-13 labeling studies reveal that the Si2C+y (y > 1) reactant ions undergo carbon exchange with acetylene, catalyzing cleavage of the carbon-carbon triple bond!

Formation of the gas-phase aluminum sulfide cations AlxS+y and their reactions with NO2

Abstract Aluminum sulfide cations were formed by direct laser vaporization of Al2S3 in a Fourier transform mass spectrometer. The most abundant series of ions is the mono-metal sulfides AlS+y (y=1–6). The Al5(S/O)+7 and Al7(S/O)+10 ion series provide evidence for surface reactions of the bulk Al2S3 with background water. Substitution of oxygen for sulfur in reactions with NO2 indicates that oxygen is more strongly bound to aluminum than sulfur. These reactions also suggest that the mono-metal ions consist of multiple S and S2 ligands bonded to the metal, with the exception of AlS+6 which may have a sulfur ring ligand.

Production of aluminum clusters by direct laser vaporization of aluminum nitride

Abstract We report the production of aluminum clusters (Al + x , x up to 62 Al − x , x up to 42) in a FTMS by direct laser vaporization of aluminum nitride. This is the first observation of pure metal clusters from a metal compound. A pressure burst composed of N and/or N 2 accompanies cluster formation and presumably helps stabilize the nascent clusters. The cluster intensity distributions are similar to those obtained using aluminum targets. The thermalized cation clusters do not react with O 2 unless they are kinetically excited. Deviations in the branching ratios from earlier beam investigations may result from pressure/timescale differences in the two experiments.

Probing the unusual kinetic behavior of Si2C+2 reactions with unsaturated and aromatic compounds

Abstract The unusual non-first-order kinetic behavior of Si2C+2 ions produced by direct laser vaporization in a Fourier transform ion cyclotron resonance mass spectrometer was probed using a variety of experimental techniques to specify the energy content of these ions. The ions apparently are formed with at least 0.8 eV of excess energy in an excited electronic state, possibly as isomers of the ground state. Reactions with a variety of substituted benzenes and unsaturated hydrocarbons were also investigated. The results of the substituted benzene reactions display a number of similarities to the reactions of Si+ with benezene or NO2, proceedings through adduct formation for the former and producing silicon oxides in the latter. Carbon-13 labeling of Si2C+2 in the reactions with 2- and 3-carbon unsaturated neutrals reveals the detailed mechanism of these reactions. The C3H4 isomers (allene and propyne) both appear to react by insertion into single bonds, leading to different products in these two cases. This is in contrast to the reactions with ethylene and acetylene, where insertion into the multiple carbon—carbon bonds is important

Mixed aluminum and indium oxide cations : controlling reactivity

Abstract Direct laser vaporization of pellets made of aluminum oxide and indium oxide was used to form mixed-metal oxide cations in a Fourier transform mass spectrometer. Indium-rich species dominate the ion abundance distribution, even when a 17-to-1 molar ratio of aluminum to indium is used. The reactivity of two series of ions, Al x In y O + ( x + y =2) and Al x In y O + 2 ( x + y =3), with N 2 O and NO 2 was studied. The presence of indium in the reactant ion acts to strongly inhibit oxidation.

Ion-molecule reactions in mixtures of trimethylaluminum and methylamines

The ion-molecule reactions of mixtures of trimethylaluminum and methylamines, to serve as a model system for group 13–15 semiconductor fabrication, were examined by using Fourier transform ion cyclotron resonance mass spectrometry. Sequential ion-molecule reactions leading to formation of multiple adduets were observed for each of the reactant mixtures investigated. Collision-induced dissociation was used to probe the adduct structures. There is evidence for hydrogen bonding between the amines and aluminum in most of the adducts studied. Rearrangement of the aluminum/nitrogen skeletons was not observed, although the aluminum/nitrogen bonds appear to be relatively strong, so that stable adducts can be formed. The monomethylamine and dimethylamine readily produce gas-phase neutral adducts with trimethylaluminum, which can be related to the basicities of the methylamines.

Formation and Reactivity of Silicon Carbide Cluster Cations

Direct laser vaporization of a mixture of silicon and graphite powders produced silicon carbide cluster cations containing 1–3 silicon atoms and 1–12 carbon atoms. Gas-phase ion-molecule reactions with acetylene and other gases were studied in the FTMS. With C2H2 the cations with 1 silicon atom behave very similarly to the carbon cluster cations, indicating a linear structure for these ions. The cations with 2 silicon atoms exhibit unusual reactivity. The initial reaction to add CH2 is very slow. With increasing time, the reaction becomes faster and forms the adduct. 13C labelling studies revealed a process of carbon exchange, which may be linked to the “activation” process just described. A structural or electronic state isomerization is believed to be the cause. Cleavage of carbon-carbon multiple bonds, dehydrogenation, deoxygenation and dehalogenation reactions of Si2C2 + are also reported. Charge transfer reactions of the initial Si2C2 + ion population were used to bracket the ionization potential of the corresponding neutral.

Workshop: The Role of Energy in Ion-Molecule Processes

A summary of the workshop on the role of energy in ion-molecule processes is given. Contributions cover the dependence of simple bimolecular reactions on kinetic and internal energy. Examples of kinetic energy release in unimolecular dissociation and internal excitation in charge transfer reactions are also discussed.