ORCID Profile
0000-0002-3166-8631
Current Organisation
University of Oxford
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Publisher: American Chemical Society (ACS)
Date: 08-12-2022
Publisher: American Chemical Society (ACS)
Date: 10-03-2011
DOI: 10.1021/JP201171P
Abstract: Far- and mid-infrared multiple photon dissociation spectroscopy has been employed to study both the structure and surface reactivity of isolated cationic rhodium clusters with surface-adsorbed nitrous oxide, Rh(n)N(2)O(+) (n = 4-8). Comparison of experimental spectra recorded using the argon atom tagging method with those calculated using density functional theory (DFT) reveals that the nitrous oxide is molecularly bound on the rhodium cluster via the terminal N-atom. Binding is thought to occur exclusively on atop sites with the rhodium clusters adopting close-packed structures. In related, but conceptually different experiments, infrared pumping of the vibrational modes corresponding with the normal modes of the adsorbed N(2)O has been observed to result in the decomposition of the N(2)O moiety and the production of oxide clusters. This cluster surface chemistry is observed for all cluster sizes studied except for n = 5. Plausible N(2)O decomposition mechanisms are given based on DFT calculations using exchange-correlation functionals. Similar experiments pumping the Rh-O stretch in Rh(n)ON(2)O(+) complexes, on which the same chemistry is observed, confirm the thermal nature of this reaction.
Publisher: Informa UK Limited
Date: 24-03-2019
Publisher: American Physical Society (APS)
Date: 27-04-2018
Publisher: American Chemical Society (ACS)
Date: 31-10-2023
Publisher: SAGE Publications
Date: 04-2009
DOI: 10.1255/EJMS.945
Abstract: The reactions of niobium cluster cations, Nb + n ( n = 2–19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters ( n 9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters ( n 11) is sequential NO chemisorption. Clusters n = 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N 2 loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size.
Publisher: American Chemical Society (ACS)
Date: 25-08-2006
DOI: 10.1021/JP062603O
Abstract: The structure, energetics, and interconversion of isomers of Rh(6) and Rh(6)(+) are studied by using density functional theory with Gaussian basis sets, using guess structures derived from basin-hopping simulations, and obtained by using the Sutton-Chen potential. A large range of spin multiplicities is considered for each isomer. Our calculations suggest two low-lying structures as possible structural isomers: a square bipyramid and a trigonal prism. The reactivity of these two candidate structural isomers with respect to adsorption of nitric oxide is studied via location of reaction transition states and calculation of reaction barriers. Similarities and differences with surface reaction studies are highlighted. These data provide powerful evidence that structural isomerism, and not different spin states, is responsible for the observed biexponential reaction kinetics.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0CP02800B
Abstract: Infrared multiple-photon dissociation spectroscopy has been applied to study Pt n (N 2 O) + ( n = 1–8) clusters which represent entrance-channel complexes on the reactive potential energy surface for nitrous oxide decomposition on platinum.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CP02862J
Abstract: We report a combined experimental and computational study of carbon dioxide activation at gas-phase Ho + and HoO + centres.
Publisher: AIP Publishing
Date: 06-01-2010
DOI: 10.1063/1.3285266
Abstract: The geometric structure of the Rh8+ cation is investigated using a combination of far-infrared multiple photon dissociation spectroscopy and density functional theory (DFT) calculations. The energetic ordering of the different structural motifs is found to depend sensitively on the choice of pure or hybrid exchange functionals. Comparison of experimental and calculated spectra suggests the cluster to have a close-packed, bicapped octahedral structure, in contrast to recent predictions of a cubic structure for the neutral cluster. Our findings demonstrate the importance of including some exact exchange contributions in the DFT calculations, via hybrid functionals, when applied to rhodium clusters, and cast doubt on the application of pure functionals for late transition metal clusters in general.
Publisher: Elsevier BV
Date: 02-2009
Publisher: Springer Science and Business Media LLC
Date: 30-10-2017
Publisher: AIP Publishing
Date: 23-09-2008
DOI: 10.1063/1.2981810
Abstract: Density functional theory is used to investigate the structures of cationic rhodium cluster oxides, Rh6Om+ (m=1,4). On the monoxide and dioxide, the oxygen atoms occupy bridge sites, while on trioxide and tetroxide clusters, high-coordination sites are favored. A range of spin multiplicities are investigated for each cluster, with high spin multiplicities found to be less favored for the oxides compared with the naked metal clusters. The dissociation of nitric oxide on low-energy isomers of Rh6O4+ is investigated and found to be unfavorable compared to molecular adsorption due to a combination of thermodynamic and kinetic factors. These calculations are consistent with, and help to account for, the experimentally observed reactivity of rhodium and rhodium oxide clusters with nitric oxide [M. S. Ford et al., Phys. Chem. Chem. Phys. 7, 975 (2005)].
Publisher: American Chemical Society (ACS)
Date: 29-09-2017
Abstract: Gas-phase metal ion-ligand complexes offer model environments to study molecular interactions that are key to many catalytic processes. Here, we present a combined experimental and computational study of M
Publisher: AIP Publishing
Date: 25-04-2017
DOI: 10.1063/1.4979979
Abstract: Neutral metal-containing molecules and clusters present a particular challenge to velocity map imaging techniques. Common methods of choice for producing such species—such as laser ablation or magnetron sputtering—typically generate a wide variety of metal-containing species and, without the possibility of mass-selection, even determining the identity of the dissociating moiety can be challenging. In recent years, we have developed a velocity map imaging spectrometer equipped with a laser ablation source explicitly for studying neutral metal-containing species. Here, we report the results of velocity map imaging photofragmentation studies of MoO and CrO. In both cases, dissociation at the two- and three-photon level leads to fragmentation into a range of product channels, some of which can be confidently assigned to particular Mo* (Cr*) and O atom quantum states. Analysis of the kinetic energy release spectra as a function of photon energy allows precise determination of the ground state dissociation energies of MoO (=44 064 ± 133 cm−1) and CrO (=37 197 ± 78 cm−1), respectively.
Publisher: Wiley
Date: 12-10-2018
Publisher: Elsevier BV
Date: 2019
Publisher: American Chemical Society (ACS)
Date: 03-01-2017
Abstract: The structures of gas-phase M
Publisher: Informa UK Limited
Date: 15-09-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B618299B
Abstract: The reactions of gas phase rhodium clusters, Rhn+/- (n<30), with nitrous oxide, N2O, have been investigated under single collision conditions by Fourier transform ion cyclotron resonance mass spectrometry. The only significant reaction observed is the sequential generation of oxides. Absolute rate constants for the reactions of all clusters have been determined and, in the case of the cationic clusters especially, they exhibit large fluctuations as a function of cluster size with local minima observed for n=5, 19, 28. Striking similarities are observed with the variation in rate constants for these clusters in reactions with small hydrocarbons (C. Adlhart and E. Uggerud, J. Chem. Phys., 2005, 123, 214709). Corresponding size effects are also observed but are less marked in the reactions of the anionic clusters. The reactions of several clusters exhibit marked deviations from simple pseudo-first-order kinetics suggesting the presence of multiple isomeric forms: Rh11+, Rh12+ and Rh8- exhibit characteristic biexponential decays which are interpreted in terms of the existence of different structural forms of the cluster which have markedly different reactivity. By contrast, Rh6+, Rh7+ and Rh8+ show rates which apparently increase with time, probably due to collisional activation. Thermalisation of the clusters prior to reaction by exposure to pulses of argon results in changes to the kinetics of these anomalous systems which can be explained in terms of collision induced isomerisation.
Publisher: American Physical Society (APS)
Date: 17-10-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8CP05995K
Abstract: The structures of gas-phase group nine cation–nitrous oxide metal–ligand complexes, M + (N 2 O) n (M = Co, Rh, Ir n = 2–7) have been determined by a combination of infrared photodissociation spectroscopy and density functional theory.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CP05195K
Abstract: Infrared multiple-photon dissociation spectroscopy reveals the nature of nitrous oxide binding to metal clusters.
Publisher: American Chemical Society (ACS)
Date: 03-06-2020
Publisher: American Chemical Society (ACS)
Date: 15-01-2010
DOI: 10.1021/JA907496C
Abstract: Multiple photon infrared excitation of size-selected Rh(6)N(2)O(+) clusters drives surface chemistry resulting in partially oxidized clusters.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CP02120E
Abstract: Velocity map imaging has been employed to study multi-photon fragmentation of vanadium monoxide (VO) via the C 4 Σ − state.
Publisher: AIP Publishing
Date: 28-11-2018
DOI: 10.1063/1.5041381
Abstract: The photodissociation dynamics of CH3I and CH2ClI at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815 nm probe pulse. Fragment ion momenta over a wide m/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH2ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion.
Publisher: AIP Publishing
Date: 07-12-2010
DOI: 10.1063/1.3509778
Abstract: The geometric structures of small cationic rhodium clusters Rh \\documentclass[12pt]{minimal}\\begin{document}$_n^+$\\end{document}n+ (n = 6–12) are investigated by comparison of experimental far-infrared multiple photon dissociation spectra with spectra calculated using density functional theory. The clusters are found to favor structures based on octahedral and tetrahedral motifs for most of the sizes considered, in contrast to previous theoretical predictions that rhodium clusters should favor cubic motifs. Our findings highlight the need for further development of theoretical and computational methods to treat these high-spin transition metal clusters.
Publisher: American Physical Society (APS)
Date: 16-07-2021
Publisher: Wiley
Date: 12-10-2018
Abstract: Infrared multiple photon dissociation spectroscopy (IR-MPD) has been employed to determine the nature of CO
Publisher: AIP Publishing
Date: 24-09-2015
DOI: 10.1063/1.4931486
Abstract: The near ultraviolet photodissociation dynamics of silver atom—rare gas dimers have been studied by velocity map imaging. Ag–RG (RG = Ar, Kr, Xe) species generated by laser ablation are excited in the region of the C (2Σ+)←X (2Σ+) continuum leading to direct, near-threshold dissociation generating Ag* (2P3/2) + RG (1S0) products. Images recorded at excitation wavelengths throughout the C (2Σ+)←X (2Σ+) continuum, coupled with known atomic energy levels, permit determination of the ground X (2Σ+) state dissociation energies of 85.9 ± 23.4 cm−1 (Ag–Ar), 149.3 ± 22.4 cm−1 (Ag–Kr), and 256.3 ± 16.0 cm−1 (Ag–Xe). Three additional photolysis processes, each yielding Ag atom photoproducts, are observed in the same spectral region. Two of these are markedly enhanced in intensity upon seeding the molecular beam with nitrous oxide, and are assigned to photodissociation of AgO at the two-photon level. These features yield an improved ground state dissociation energy for AgO of 15 965 ± 81 cm−1, which is in good agreement with high level calculations. The third process results in Ag atom fragments whose kinetic energy shows anomalously weak photon energy dependence and is assigned tentatively to dissociative ionization of the silver dimer Ag2.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Stuart Mackenzie.