Nigel G. Gotts

Bio: Nigel G. Gotts is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Cluster (physics) & Fullerene. The author has an hindex of 13, co-authored 13 publications receiving 1557 citations.

Carbon cluster cations with up to 84 atoms: structures, formation mechanism, and reactivity

Abstract: Carbon clusters are generated by laser desorption. Mass-selected beams are then pulse injected into an ion chromatography (IC) device. This device temporally and spatially separates the beam into its isomeric components. Arrival time distributions (ATDs) are then measured at the detector. From these distributions, accurate mobilities are obtained for each isomeric component, along with the the fractional abundance of each isomer. Different isomer structures are calculated using quantum chemical methods. A Monte Carlo technique uses these structures to obtain accurate theoretical mobilities. Comparison of theory with experiment allows unambiguous structural assignment of the various families of isomers present in the cluster beam. The results indicate that, for carbon cluster cations, linear structures exist up to C[sub 10[sup +]]. Several families of planar ring systems begin with monocyclic rings (ring I), which first appear at C[sub 7[sup +]], and persist beyond C[sub 40[sup +]]. Bicyclic rings (ring II) are first observed at C[sub 21[sup +]] and persist beyond C[sub 40[sup +]], followed by tricyclic rings (ring III, initiated at C[sub 30[sup +]]) and tetracyclic rings (ring IV, initiated at C[sub 40[sup +]]). A 3-dimensional family we label as 3-D rings begins at C[sub 29[sup +]], whose structure is not yet unambiguouslymore » assigned. This family never exceeds 5% of the ions at any cluster size. Finally, the first fullerene is observed at C[sub 30[sup +]], with this family dominating above C[sub 50[sup +]]. 32 refs., 14 figs., 4 tabs.« less

Experimental evidence for the formation of fullerenes by collisional heating of carbon rings in the gas phase

Abstract: THE discovery1–6 of the spherical carbon cage compound buck-minsterfullerene (C60) and the recent development of methods to produce it in bulk7 have led to an explosion in research in the physical and chemical properties of this unique species8,9. Nevertheless, the question of the formation mechanism of C60 (or of the other fullerenes) is still far from settled. We have shown elsewhere that carbon clusters in the gas phase develop from linear chains to planar ring systems to fullerenes as their size increases. One can easily envisage the transformation from chains to rings, but how the three-dimensional near-spherical fullerenes evolve from large planar rings is not obvious. Here we show that 'heating' these large ring systems above their 'melting' point leads to 100% fullerene formation accompanied by the evaporation of a small carbon fragment (C1 or C3 for odd systems and C2 for even systems). We propose a mechanism, based on these data, for efficient C60 production in carbon arcs.

Isomers of Small Carbon Cluster Anions: Linear Chains with up to 20 Atoms

Abstract: The structure of small carbon cluster anions, C n - (4 ≤ n ≤ 20), was investigated with the use of ion chromatography. With this technique, both the existence and the relative amounts of possible structural isomers can be determined. More than 99% of the ions C5- to C9- were found to be linear under these experimental conditions. Starting with C10-, a monocyclic isomer was observed, and linear and moncyclic structures coexisted from C10- through at least C20-. This result is in contrast to previous work on positive ions, which showed the existence of linear isomers from C5+ to C10+, with linear and cyclic isomers coexisting only from C7+ to C10+. Above C10+, no linear clusters were observed.

Ion mobility-mass spectrometry.

Abstract: This review article compares and contrasts various types of ion mobility-mass spectrometers available today and describes their advantages for application to a wide range of analytes. Ion mobility spectrometry (IMS), when coupled with mass spectrometry, offers value-added data not possible from mass spectra alone. Separation of isomers, isobars, and conformers; reduction of chemical noise; and measurement of ion size are possible with the addition of ion mobility cells to mass spectrometers. In addition, structurally similar ions and ions of the same charge state can be separated into families of ions which appear along a unique mass-mobility correlation line. This review describes the four methods of ion mobility separation currently used with mass spectrometry. They are (1) drift-time ion mobility spectrometry (DTIMS), (2) aspiration ion mobility spectrometry (AIMS), (3) differential-mobility spectrometry (DMS) which is also called field-asymmetric waveform ion mobility spectrometry (FAIMS) and (4) traveling-wave ion mobility spectrometry (TWIMS). DTIMS provides the highest IMS resolving power and is the only IMS method which can directly measure collision cross-sections. AIMS is a low resolution mobility separation method but can monitor ions in a continuous manner. DMS and FAIMS offer continuous-ion monitoring capability as well as orthogonal ion mobility separation in which high-separation selectivity can be achieved. TWIMS is a novel method of IMS with a low resolving power but has good sensitivity and is well intergrated into a commercial mass spectrometer. One hundred and sixty references on ion mobility-mass spectrometry (IMMS) are provided.

Ion mobility-mass spectrometry analysis of large protein complexes.

Abstract: Here we describe a detailed protocol for both data collection and interpretation with respect to ion mobility-mass spectrometry analysis of large protein assemblies. Ion mobility is a technique that can separate gaseous ions based on their size and shape. Specifically, within this protocol, we cover general approaches to data interpretation, methods of predicting whether specific model structures for a given protein assembly can be separated by ion mobility, and generalized strategies for data normalization and modeling. The protocol also covers basic instrument settings and best practices for both observation and detection of large noncovalent protein complexes by ion mobility-mass spectrometry.

Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

Abstract: Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

Clusters: Structure, Energetics, and Dynamics of Intermediate States of Matter

Abstract: The field of cluster research can trace its origins back to the mid-nineteenth century when early studies of colloids, aerosols, and nucleation phenomena were reported. The field underwent a resurgence of interest several decades ago when well-defined clusters were observed in supersonic expansions that could be investigated using mass spectrometers. The advent of the laser provided a new dimension, enabling detailed spectroscopic observations through the probing of systems of varying size and degree of solvation. Modern interest derives from recognition that interrogating clusters provides a way of studying the energetics and dynamics of intermediate states of matter as cluster systems evolve from the gas toward the condensed state. Herein, we endeavor to highlight some of the significant advances which have been made during the past several decades that have led to a nearly explosive growth of interest in the field of cluster science. Finally, we conclude that the field will continue to expand through i...