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In this article, recent cluster—surface collision experiments are reviewed from the perspective of fullerene research. A detailed description of the method and the reflectron time-of-flight surface collider (reflectron collider), designed and built in Los Angeles, will be given first, to show how pulsed cluster-ion-beams are mass and energy selected, collided with specific surfaces and the various outcomes studied. In the second part, we outline several applications together with the scientific impact surface collision experiments have had on several fullerene-related research subjects. This includes impact-induced dissociation experiments, to probe stability and structural resilience, rebound velocity distributions from solid surfaces to reveal energetic and dynamic aspects of the scattering process, and rates of delayed electron emission from impact-heated fullerenes. Impact experiments also have turned out to be a useful tool to examine structural hypotheses as demonstrated on coalescence products from fullerene—fullerene reactions, fullerene derivatives and on metallo-fullerenes.

Recent experiments have demonstrated that large fullerenes can form by coalescence in the hot and dense vapor produced by pulsed UV-laser desorption of a fullerene film. The abundance spectra exhibit masses both at and close to the primary coalescence product. We suggest a rate equation that reproduces this pattern, applicable to the nearly symmetric abundance distributions observed in coalescence with high laser fluence and also to the strongly asymmetric case of coalescence with low fluence. The equation is parameterized by three rates, which in the completely symmetric and in the completely asymmetric case reduces to two. In these two cases the relative abundances can be expressed by a single dimensionless parameter.

Thermal emission of electrons is ordinarily considered to be exclusively a property of macroscopic condensed matter. Slow electron emission occurs for certain small metal clusters as well as for silicon and carbon clusters, but the nature of this process has not been established. Electron emission rates have been obtained and analyzed from extensive real-time measurements on negatively charged fullerenes for several sizes and over a wide, continuous range of energies. These results confirm that delayed electron emission is a simple activated process that depends strongly on the internal energy and size of the cluster and that it has a common underlying mechanism, independent of size. However, the Arrhenius form deduced is inconsistent with the emission rate theory used for bulk surfaces. These results allow the question of the correct microscopic description of this newly observed electron emission process to be assessed.

This article reviews recent work in Los Angeles on elementary processes in fullerene vapors. The production of fullerene molecules typically involves extreme high-temperature conditions and processes which are poorly understood at date [1–3]. Once generated, these molecules may represent the most stable molecules known [4,5]. In a recent work [C. Yeretzian et al., Nature 359, 44 (1992)] we presented clear evidence for coalescence reactions between fullerene molecules. Mass spectrometric measurements on hot, dense vapors of small fullerenes (C60 and C70) reveal the formation of stable higher fullerenes which are multiples of the initial masses. These processes are shown to occur in the gas-phase rather than in the solid film and their dependences on laser fluence and He-gas pressure are investigated. Three distinct reactions are proposed—coalescence, emission and capture—to account for the observed distributions at higher fullerene sizes. Specifically, the heat of coalescence is released through emission of small, even-numbered fragments which, in a very dense vapor, are efficiently captured by other coalesced fullerenes. These findings have implications for the long-time stability of the fullerene vapor, and for the mechanism of fullerene formation and growth, and may open new ways to the synthesis of selected higher fullerenes and encapsulation compounds.

The disintegration and coalescence processes of fullerenes have not yet been established, although certain aspects have been known for years. For example, the energy required to fragment C 60 has been calculated to lie in the 11–14 eV range, making it the most stable large molecule known, while reported experimental values are in the 4.5–7 eV range. In this report, we show that surface-impact heating of fullerene-ion beams, when properly calibrated, gives values in agreement with theory. In the last section, new mass spectrometric results on the coalescence reactions of hot fullerene vapors are presented.

The soluble molecule La2C80 recently reported by Alvarez et al. exhibits a robustness similar to other fullerenes. It survives intact for ≈ 10−6s following impact against solid surfaces Si(100) at up to 200 eV, yielding an estimate Ef>4 eV for fragmentation processes. The high threshold for electron emission suggests that the electron affinity in La2C−80 is significantly larger than in C60. These facts seem to rule out an external site for either La atom and disfavor a network-site interpretation, and thus favor endohedral (encapsulation) sites. Among the possible cages, the Ih-C80 fullerene appears to be highly favorable for the oxidation state (La3+)2C6−80.

In this article, a method for high-resolution laser spectroscopy of ions—termed ZEro-Kinetic Energy spectroscopy (ZEKE)— is reviewed. Emphasis will be put on a more recent, mass-selective version (mass-analyzed ZEKE). A detailed description of the apparatus, designed and built at the Technische Universitat Munchen, will first be given. In a second part, we outline two applications which are particularly suited to illustrate the potential of the method. We hope to demonstrate to the mass spectrometry community the close connection between a ZEKE spectrometer and a conventional reflectron time-of-flight mass spectrometer (TOF-MS). Adding one single electrostatic field lens to the extraction field region of a TOF-MS allows to go far beyond mass analysis, distinguishing, for example, between isomeric structures or determining the geometric structure of molecular ions.

The preparation of a cup of coffee may vary between countries, cultures and individuals. Here, an analysis of nine different extraction methods is presented regarding analytical and sensory aspects for four espressi and five lunghi. This comprised espresso and lungo from a semi-automatic coffee machine, espresso and lungo from a fully automatic coffee machine, espresso from a single- serve capsule system, mocha made with a percolator, lungo prepared with French Press extraction, filter coffee and lungo extracted with a Bayreuth coffee machine. Analyti- cal measurements included headspace analysis with HS SPME GC/MS, acidity (pH), titratable acidity, content of fatty acids, total solids, refractive indices (expressed in � Brix), caffeine and chlorogenic acids content with HPLC. Sensory analysis included visual, aroma, flavor and textural attributes as well as aftersensation. The technical differ- ences in the extraction methods led to a higher concen- tration of the respective quantities in the espressi than in the lunghi. Regarding the contents per cup of coffee, the lunghi generally had a higher content than the espressi. The extraction efficiency of the respective compounds was mainly driven by their solubility in water. A higher amount of water, as in the extraction of a lungo, generally led to higher extraction efficiency. Comparing analytical data with sensory profiles, the following positive correlations were found total solids $ texture/body, headspace inten- sity $ aroma intensity, concentrations of caffeine/chloro- genic acids $ bitterness and astringency.

A review with 111 refs. presenting exptl. aspects of metal-cluster work including: supersonic- mol.- beam technol.; laser spectroscopy; mass spectroscopy; and low- and high-temp. matrix-isolation expts. The exptl. results discussed include: stability of cluster sizes; selectivity of the heterometallic bond; elec. and magnetic properties from the atom to the bulk; insulator-metal transitions; and size-dependent chem. and catalytic properties. Quantum chem. and ab initio mol. dynamics models are discussed. [on SciFinder (R)]

Recent mass spectroscopic studies of continuous cluster beams resulting from supersonic expansions of alkali metal vapor have led to the postulation of islands of enhanced thermodynamic stability among the clusters produced. We discuss the various assumptions being made in converting ion abundances measured in these mass spectra into information about neutral stabilities. In this connection a number of experiments are described which allow insight into unimolecular dissociation of alkali cluster ions and into neutral cluster growth.

Controversy regarding the interpretation of photoionization efficiency measurements obtained for alkali clusters provided impetus for higher-resoln. (3.3 nm) studies . The new data cover the full range of cluster sizes: Nax, x

This article reviews the evolution of the UCLA fullerene research over the past two years from the perspective of laser desorption mass spectrometry (LDMS). As a fast and sensitive analytical method, it has critically contributed to a wide range of fullerene related research projects. Immediately after the discovery of a method for making C60, C70 and selected higher fullerenes in macroscopic amounts, a concerted effort in different laboratories led to the isolation and structure determination of C76, C78, C82 and tentatively C84. Simultaneously with the work on pure fullerene, important progress was achieved in the synthesis of metallofullerenes and derivatized fullerenes. LDMS continually documented progress or failure in extraction, isolation and synthesis and helped to plan future research. Recently, synthesis of C60 and larger fullerenes from precursors, e.g., C18(CO)6, and coalescence reactions of fullerenes, induced by high fluence of the desorption laser, introduced a new aspect of this otherwise exclusively analytical method.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

During the course of mass spectral studies on the stability of bimetallic systems, an exceptionally abundant and stable Na6Pb cluster was discovered. For given exptl. conditions, an intense mol. beam consisting exclusively of the particle Na6Pb is generated via self-assembly from a mixed vapor of sodium and lead. While this observation is reminiscent of the discovery of C60 or Tl8C12, Na6Pb represents the first example of a binary finite-size 'alloy' ( 0.5 nm diam.) exhibiting such extraordinary stability. [on SciFinder (R)]

Liquid–gas partition coefficients (HLC) of volatile organic compounds (VOCs) in water–air systems are determined using a novel dynamic approach by coupling a stripping cell directly to a proton-transfer-reaction mass spectrometer (PTR–MS). Two complementary set-ups are evaluated, one suited for determining HLCs of highly volatile compounds (

International audience; The perception of thousands of odours by about 380 human olfactory receptors (ORs) results from a combinatorial coding, in which one OR recognizes multiple odorants and odorants are recognized by different combinations of ORs. We used data of 95 odorant molecules tested on two human ORs, OR1G1 (class II) and OR52D1 (class I), to perform a 3D molecular modelling study of ligands using Catalyst/HypoGen software. The sorting-out procedure previously used for OR1G1 ligands was transposed to OR52D1 ligands. The 3D-QSAR models obtained for OR1G1 and OR52D1 ligands essentially differ by distance between their features. This result suggests a path to decipher the odotopes of OR1G1 and OR52D1 agonists in order to investigate the role of ORs in olfactory coding.

International audience; Rice from two scented (Aychade, Fidji) and one nonscented (Ruille) cultivars from Camargue area (France) together with one Asian scented rice (Thai) were cooked and volatile compounds were extracted by dichloromethane/pentane (1;2, v/v) solvent mixture. 40 odorous compounds were noticed during GC-O analysis of the organic extracts, amongst which oct-1-en-3-one and 2-acetyl-1-pyrroline were altmost constantly perceived. Hierarchical cluster analysis (HCA) of perceived odours enabled to distinguish the groups of rice cultivars. 60 compounds were identified and quantified by GC-MS. New odour-active components of cooked rice were detected for the first time including oct-3-en-2-one, 2-methylpropanoic acid, y-decalactone and o-decalactone. A principal component analysis (PCA) differentiated scented cultivars from a non-scented one and scented rice cultivars from Camargue from Thai sample.