Complexes with Atomic Gold Ions: Efficient Bis-Ligand Formation.

Complexes of atomic gold with a variety of ligands have been formed by passing helium nanodroplets (HNDs) through two pickup cells containing gold vapor and the vapor of another dopant, namely a rare gas, a diatomic molecule (H, N, O, I, P), or various polyatomic molecules (HO, CO, SF, CH, adamantane, imidazole, dicyclopentadiene, and fullerene). The doped HNDs were irradiated by electrons; ensuing cations were identified in a high-resolution mass spectrometer. Anions were detected for benzene, dicyclopentadiene, and fullerene.

Atomic Gold Ions Clustered with Noble Gases: Helium, Neon, Argon, Krypton, and Xenon.

High-resolution mass spectra of helium droplets doped with gold and ionized by electrons reveal HeAu cluster ions. Additional doping with heavy noble gases results in NeAu, ArAu, KrAu, and XeAu cluster ions. The high stability predicted for covalently bonded ArAu, KrAu, and XeAu is reflected in their relatively high abundance.

Hydrogenated Gold Clusters from Helium Nanodroplets: Cluster Ionization and Affinities for Protons and Hydrogen Molecules.

We report the mass spectrometric detection of hydrogenated gold clusters ionized by electron transfer and proton transfer. The cations appear after the pickup of hydrogen molecules and gold atoms by helium nanodroplets (HNDs) near zero K and subsequent exposure to electron impact. We focus on the size distributions of the gold cluster cations and their hydrogen content, the electron energy dependence of the ion yield, patterns of hydrogenated gold cluster cation stability, and the presence of "magic" clusters.

Charged Clusters of C and Au or Cu: Evidence for Stable Sizes and Specific Dissociation Channels.

We have doped helium nanodroplets with C and either gold or copper. Positively or negatively charged (C) M ions (M = Au or Cu) containing up to ≈10 fullerenes and ≈20 metal atoms are formed by electron ionization. The abundance distributions extracted from high-resolution mass spectra reveal several local anomalies.

A combined experimental and theoretical investigation of Cs ions solvated in He clusters.

Solvation of Cs ions inside helium droplets has been investigated both experimentally and theoretically. On the one hand, mass spectra of doped helium clusters ionized with a crossed electron beam, HeCs, have been recorded for sizes up to N = 60. The analysis of the ratio between the observed peaks for each size N reveals evidences of the closure of the first solvation shell when 17 He atoms surround the alkali ion.

Spectroscopy of corannulene cations in helium nanodroplets.

Helium tagging in action spectroscopy is an efficient method for measuring the absorption spectra of complex molecular ions with minimal perturbations to the gas phase spectra. We have used superfluid helium nanodroplets doped with corannulene to prepare cations of these molecules complexed with different numbers of He atoms. In total we identify 13 different absorption bands from corannulene cations between 5500 Å and 6000 Å.

Uptake and accommodation of water clusters by adamantane clusters in helium droplets: interplay between magic number clusters.

We report an experimental study of water clusters as guests in interactions with clusters of adamantane (Ad) as hosts that occur in doped helium droplets at extremely low temperatures. Separate experiments with pure water as dopant showed ready formation of a distribution of water clusters (H2O)mH+ that peaks at m = 11 and extends beyond m = 100 with local maxima at m = 4, 11, 21, 28 and 30 with (H2O)21H+ being the most anomalous and showing the greatest stability with respect to clusters immediately adjacent in water content. When adamantane is also added as a dopant, extensive hydration is seen in the formation of water/adamantane clusters, (H2O)mAdn+; magic number clusters (H2O)21Adn+ are seen for all the adamantane clusters.

Doubly charged coronene clusters-Much smaller than previously observed.

The smallest doubly charged coronene cluster ions reported so far, Cor, were produced by charge exchange between bare coronene clusters and He [H. A. B.

Highly Stable [CAuC] Dumbbells.

Ionic complexes between gold and C have been observed for the first time. Cations and anions of the type [Au(C)] are shown to have particular stability. Calculations suggest that these ions adopt a C-Au-C sandwich-like (dumbbell) structure, which is reminiscent of [XAuX] ions previously observed for much smaller ligands.

The adsorption of helium atoms on small cationic gold clusters.

Adducts formed between small gold cluster cations and helium atoms are reported for the first time. These binary ions, Aun+Hem, were produced by electron ionization of helium nanodroplets doped with neutral gold clusters and were detected using mass spectrometry. For a given value of n, the distribution of ions as a function of the number of added helium atoms, m, has been recorded.

Complexes of gold and imidazole formed in helium nanodroplets.

We have studied complexes of gold atoms and imidazole (CNH, abbreviated Im) produced in helium nanodroplets. Following the ionization of the doped droplets we detect a broad range of different AuIm complexes, however we find that for specific values of m certain n are "magic" and thus particularly abundant. Our density functional theory calculations indicate that these abundant clusters sizes are partially the result of particularly stable complexes, e.

Preheated composite resin used as a luting agent for indirect restorations: effects on bond strength and resin-dentin interfaces.

Purpose: The aim of this study was to evaluate the effect of preheating composite resins used as luting agents for indirect restorations on microtensile bond strength (µTBS) and adhesive interfaces.

Material And Methods: Fifty sound extracted third molars were used. Ten experimental groups were formed with three different luting agents: one resin cement (RelyX ARC) and two composite resins (Venus and Z250 XT).

Effect of erosive challenges on deciduous teeth undergoing restorative procedures with different adhesive protocols - an in vitro study.

To evaluate the effect of erosive challenges on the tooth- restoration interface of deciduous teeth treated with different adhesive protocols. Deciduous molars were cut mesiodistally, then embedded, abraded and polished (n=80). Samples were randomly divided according to the adhesive system used into: G1 (Adper Single Bond2®, etch-and-rinse), G2 (Universal Single Bond®, self-etching), G3 (OptibondFL®, etch-and-rinse with Fluoride) and G4 (BondForce®, self-etching with Fluoride).

The structure of coronene cluster ions inferred from H uptake in the gas phase.

Mass spectra of helium nanodroplets doped with H and coronene feature anomalies in the ion abundance that reveal anomalies in the energetics of adsorption sites. The coronene monomer ion strongly adsorbs up to n = 38 H molecules indicating a commensurate solvation shell that preserves the D symmetry of the substrate. No such feature is seen in the abundance of the coronene dimer through tetramer complexed with H; this observation rules out a vertical columnar structure.

Positively and Negatively Charged Cesium and (C) Cs Cluster Ions.

We report on the formation and ionization of cesium and CCs clusters in superfluid helium nanodroplets. Size distributions of positively and negatively charged (C) Cs ions have been measured for ≤ 7, ≤ 12. Reproducible intensity anomalies are observed in high-resolution mass spectra.

Ordered phases of ethylene adsorbed on charged fullerenes and their aggregates.

In spite of extensive investigations of ethylene adsorbed on graphite, bundles of nanotubes, and crystals of fullerenes, little is known about the existence of commensurate phases; they have escaped detection in almost all previous work. Here we present a combined experimental and theoretical study of ethylene adsorbed on free C and its aggregates. The ion yield of [Formula: see text] measured by mass spectrometry reveals a propensity to form a structurally ordered phase on monomers, dimers and trimers of C in which all sterically accessible hollow sites over carbon rings are occupied.

Microtensile bond strength of etch-and-rinse and self-etch adhesives to artificially created carious dentin.

This article evaluates a pH-cycling model for simulation of caries-affected and caries-infected dentin (CAD and CID, respectively) surfaces, by comparing the bond strength of an etch-and-rinse and a self-etch adhesive system. For both adhesives, bonding to sound dentin (SD) showed that the microtensile bond strength (μTBS) values of SD, CAD, and CID were SD > CAD > CID (P < 0.05).

Dissociative electron attachment to the nitroamine HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine).

In the present study, dissociative electron attachment (DEA) measurements with gas phase HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, C4H8N8O8, have been performed by means of a crossed electron-molecular beam experiment. The most intense signals are observed at 46 and 176 u and assigned to NO2(-) and C3H6N5O4(-), respectively. Anion efficiency curves for 15 negatively charged fragments have been measured in the electron energy region from about 0-20 eV with an energy resolution of ~0.

Electron-driven ionization of large methanol clusters in helium nanodroplets.

The electron-driven ionization of helium droplets doped with pure methanol and ethanol clusters has been investigated for the first time using high resolution mass spectrometry. Large clusters are readily accessible by this route, with up to 100 alcohol molecules seen in the present study. The mass spectra for the doped helium droplets show many similarities with previous gas phase mass spectrometric studies of methanol and ethanol clusters.