139 results on '"Mackenzie, Stuart R."'
Search Results
102. Dramatic size effects and evidence of structural isomers in the reactions of rhodium clusters, Rhn±, with nitrous oxide
- Author
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Harding, Daniel, primary, Ford, Mark S., additional, Walsh, Tiffany R., additional, and Mackenzie, Stuart R., additional
- Published
- 2007
- Full Text
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103. Chemical Reactivity on Gas-Phase Metal Clusters Driven by Blackbody Infrared Radiation.
- Author
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Parry, Imogen S., Kartouzian, Aras, Hamilton, Suzanne M., Balaj, O. Petru, Beyer, Martin K., and Mackenzie, Stuart R.
- Subjects
CHEMICAL reactions ,METAL clusters ,INFRARED radiation ,NITROUS oxide ,FOURIER transforms - Abstract
We report the observation of chemical reactions in gas-phase Rh
n (N2 O)m + complexes driven by absorption of blackbody radiation. The experiments are performed under collision-free conditions in a Fourier transform ion cyclotron resonance mass spectrometer. Mid-infrared absorption by the molecularly adsorbed N2 O moieties promotes a small fraction of the cluster distribution sufficiently to drive the N2 O decomposition reaction, leading to the production of cluster oxides and the release of molecular nitrogen. N2 O decomposition competes with molecular desorption and the branching ratios for the two processes show marked size effects, reflecting variations in the relative barriers. The rate of decay is shown to scale approximately linearly with the number of infrared chromophores. The experimental findings are interpreted in terms of calculated infrared absorption rates assuming a sudden-death limit. [ABSTRACT FROM AUTHOR]- Published
- 2015
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104. Durch Schwarzkörperstrahlung angetriebene chemische Reaktivität auf Metallclustern in der Gasphase.
- Author
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Parry, Imogen S., Kartouzian, Aras, Hamilton, Suzanne M., Balaj, O. Petru, Beyer, Martin K., and Mackenzie, Stuart R.
- Abstract
Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2015
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- View/download PDF
105. Preparing transition-metal clusters in known structural forms: The mass-analyzed threshold ionization spectrum of V3
- Author
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Ford, Mark S., primary and Mackenzie, Stuart R., additional
- Published
- 2005
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106. Intracluster stereochemistry in van der Waals complexes: Steric effects in ultraviolet photodissociation of state-selected Ar–HOD/H2O
- Author
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Votava, Ondrej, primary, Mackenzie, Stuart R., additional, and Nesbitt, David J., additional
- Published
- 2004
- Full Text
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107. Pulsed Laser Polymerization in an Ionic Liquid: Strong Solvent Effects on Propagation and Termination of Methyl Methacrylate
- Author
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Harrisson, Simon, primary, Mackenzie, Stuart R., additional, and Haddleton, David M., additional
- Published
- 2003
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108. Unprecedented solvent-induced acceleration of free-radical propagation of methyl methacrylate in ionic liquidsElectronic supplementary information (ESI) available: Sample PLP-GPC traces and full experimental data. See http://www.rsc.org/suppdata/cc/b2/b209479g/
- Author
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Harrisson, Simon, primary, Mackenzie, Stuart R., additional, and Haddleton, David M., additional
- Published
- 2002
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109. BroadbandCavity-Enhanced Detection of Magnetic FieldEffects in Chemical Models of a Cryptochrome Magnetoreceptor.
- Author
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Neil, Simon R. T., Li, Jing, Sheppard, Dean M. W., Storey, Jonathan, Maeda, Kiminori, Henbest, Kevin B., Hore, P. J., Timmel, Christiane R., and Mackenzie, Stuart R.
- Published
- 2014
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110. Imaging the photodissociation dynamics of neutral metal clusters: copper dimer, Cu2, and copper oxide, CuO.
- Author
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Parry, Imogen S., Hermes, Alexander C., Kartouzian, Aras, and Mackenzie, Stuart R.
- Abstract
The spectroscopy and UV photodissociation dynamics of Cu
2 and CuO have been studied using a combination of one- and two-colour excitation and velocity map imaging. Resonant excitation of Cu2 via the J ← X1 Σg + transition leads to significant fragmentation which is interpreted in terms of a combination of direct dissociation of Cu2 + 2 Π produced in the resonant two-photon ionization process and dissociation of excited Cu2 states above the ionization threshold. By fitting of the kinetic energy release spectra obtained from the velocity map images, we determine a value for the dissociation energy of the cation of D0 (Cu2 + , X2 Σg + ) of 1.713 ± 0.025 eV, which, when combined with known ionization energies, yields D0 (Cu2 , X1 Σg + ) = 1.886 ± 0.026 eV. In other experiments, resonant two colour (1 + 1′) excitation of CuO via a range of excited states (C, D, F, H), yields unusually simple VMI images indicating fragmentation into a single dissociation channel which has been identified as Cu*2 D3/2 + O*1 D. Taken together, this data gives a CuO bond dissociation energy of 3.041 ± 0.030 eV. Finally, the production of Cu2 + with kinetic energy = 705 ± 75 cm−1 is tentatively interpreted as photolysis of Cu3 yielding Cu* + Cu2 X1 Σg + from which a dissociation energy of Cu3 of 0.605 ± 0.030 eV is deduced. [ABSTRACT FROM AUTHOR]- Published
- 2014
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111. Collisional Activation of N2O Decompositionand CO Oxidation Reactions on Isolated Rhodium Clusters.
- Author
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Parry, Imogen S., Kartouzian, Aras, Hamilton, Suzanne M., Balaj, O. Petru, Beyer, Martin K., and Mackenzie, Stuart R.
- Published
- 2013
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112. Structures of PlatinumOxide Clusters in the Gas Phase.
- Author
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Kerpal, Christian, Harding, Dan J., Hermes, Alexander C., Meijer, Gerard, Mackenzie, Stuart R., and Fielicke, André
- Published
- 2013
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113. Dissociation dynamics of the low-lying Rydberg states of Xe 2 : a velocity map imaging study.
- Author
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Hopkins, W. Scott and Mackenzie, Stuart R.
- Subjects
- *
DISSOCIATION (Chemistry) , *RYDBERG states , *XENON , *DIMERS , *PHOTODISSOCIATION , *VAN der Waals forces - Abstract
The photodissociation dynamics of Xe2 Rydberg states in the 76,900–80,000 cm−1 region have been studied using a combination of resonance enhanced multi-photon ionization and velocity map imaging. By monitoring photodissociation product channels as a function of excitation energy, several localized and long range perturbations of the excited states have been identified. In addition, several new band systems have been observed and assigned as the Xe2 5d 2[1/2]0° ← X , 5d 2[1/2]1° ← X , 5d 2[3/2]2° ← X , and 5d 2[7/2]3° ← X transitions. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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114. Non-linear arrhenius behaviour of the rate constants of some activation-controlled reactions of the hydrated electron in the temperature range 20–200 °C
- Author
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Buxton, George V., primary and Mackenzie, Stuart R., additional
- Published
- 1992
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115. A theoretical treatment of the à 2Σ+state of the Ar⋯HS/Ar⋯SH van der Waals complex
- Author
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Hirst, David M., Doyle, Richard J., and Mackenzie, Stuart R.
- Abstract
We present an ab initio potential energy surface for the à 2Σ+ state of the Ar⋯HS van der Waals molecule. The surface represents a fit to 196 points calculated at the RCCSD(T) level with an aug-cc-pV5Z basis set and encompasses both the Ar⋯SH and Ar⋯HS isomers. We have further calculated vibrational levels on this surface using a discrete variable representation (DVR) approach. The vibrational levels supported within the Ar⋯HS minimum are compared with levels derived from high-resolution laser induced fluorescence spectra. Predictions of vibrational levels for the Ar⋯SH isomer, which have not been observed experimentally, are also presented.
- Published
- 2004
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116. Time-resolved inner-shell photoelectron spectroscopy: From a bound molecule to an isolated atom
- Author
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Brauße, Felix, Goldsztejn, Gildas, Amini, Kasra, Boll, Rebecca, Bari, Sadia, Bomme, Cédric, Brouard, Mark, Burt, Michael, De Miranda, Barbara Cunha, Düsterer, Stefan, Erk, Benjamin, Géléoc, Marie, Geneaux, Romain, Gentleman, Alexander S., Guillemin, Renaud, Ismail, Iyas, Johnsson, Per, Journel, Loïc, Kierspel, Thomas, Köckert, Hansjochen, Küpper, Jochen, Lablanquie, Pascal, Lahl, Jan, Lee, Jason W. L., Mackenzie, Stuart R., Maclot, Sylvain, Manschwetus, Bastian, Mereshchenko, Andrey S., Mullins, Terence, Olshin, Pavel K., Palaudoux, Jérôme, Patchkovskii, Serguei, Penent, Francis, Piancastelli, Maria Novella, Rompotis, Dimitrios, Ruchon, Thierry, Rudenko, Artem, Savelyev, Evgeny, Schirmel, Nora, Techert, Simone, Travnikova, Oksana, Trippel, Sebastian, Underwood, Jonathan G., Vallance, Claire, Wiese, Joss, Simon, Marc, Holland, David M. P., Marchenko, Tatiana, Rouzée, Arnaud, and Rolles, Daniel
- Subjects
3. Good health - Abstract
Physical review / A 97(4), 043429 (2018). doi:10.1103/PhysRevA.97.043429, Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH$_3$I) is investigated by ionization above the iodine $4d$ edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules., Published by APS, Woodbury, NY
117. Coulomb-explosion imaging of concurrent CH 2 BrI photodissociation dynamics
- Author
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Burt, Michael, Boll, Rebecca, Lee, Jason W. L., Amini, Kasra, Köckert, Hansjochen, Vallance, Claire, Gentleman, Alexander S., Mackenzie, Stuart R., Bari, Sadia, Bomme, Cédric, Düsterer, Stefan, Erk, Benjamin, Manschwetus, Bastian, Müller, Erland, Rompotis, Dimitrios, Savelyev, Evgeny, Schirmel, Nora, Techert, Simone, Treusch, Rolf, Küpper, Jochen, Trippel, Sebastian, Wiese, Joss, Stapelfeldt, Henrik, de Miranda, Barbara Cunha, Guillemin, Renaud, Ismail, Iyas, Journel, Loïc, Marchenko, Tatiana, Palaudoux, Jérôme, Penent, Francis, Piancastelli, Maria Novella, Simon, Marc, Travnikova, Oksana, Brausse, Felix, Goldsztejn, Gildas, Rouzée, Arnaud, Géléoc, Marie, Geneaux, Romain, Ruchon, Thierry, Underwood, Jonathan, Holland, David M. P., Mereshchenko, Andrey S., Olshin, Pavel K., Johnsson, Per, Maclot, Sylvain, Lahl, Jan, Rudenko, Artem, Ziaee, Farzaneh, Brouard, Mark, and Rolles, Daniel
- Full Text
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118. Condensed-phase applications of cavity-based spectroscopic techniques
- Author
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Neil, Simon R. T. and Mackenzie, Stuart R.
- Subjects
543.5 ,Physical Sciences ,Biophysical chemistry ,Laser Spectroscopy ,Photochemistry and reaction dynamics ,Physical & theoretical chemistry ,cavity enhanced spectroscopy ,cavity ring-down spectroscopy ,magnetic field effect ,avian magnetoreception ,broadband cavity enhanced spectroscopy ,evanescent wave - Abstract
This thesis describes the development and application of condensed-phase cavity-based spectroscopic techniques - namely cavity ring-down spectroscopy (CRDS); cavity enhanced absorption spectroscopy (CEAS); broadband cavity enhanced absorption spectroscopy (BBCEAS) and evanescent wave (EW) variants of all three. The recently-developed cavity technique of EW-broadband cavity enhanced absorption spectroscopy (EW-BBCEAS) has been used—in combination with a supercontinuum source (SC) and a sensitive, fast readout CCD detector—to record of the full visible spectrum (400–700 nm) of a silica-liquid interfacial layer (with an effective thickness ca. 1 µm), at rapid acquisition rates (> 600 Hz) that are sufficient to follow fast kinetics in the condensed phase, in real time. The sensitivity achieved (A
min = 3.9 x 10-5 ) is comparable with previous EW-CRDS and EW-CEAS studies, but the spectral region accessed in this broadband variant is much larger. The study of liquid|air interfaces using EW cavity-based techniques is also illustrated for the first time. The first application of BBCEAS to the analysis of microfluidic samples, flowing through a microfluidic chip, is illustrated. Proof-of-principle experiments are presented, demonstrating the technique’s ability to provide full visible broadband spectral measurements of flowing microfluidic droplets, with both high detection sensitivity (αmin < 10-2 cm-1 ) and excellent spatial and temporal resolution: an SC light source and sensitive, fast readout CCD allowed measurement repetition rates of 273 Hz, whilst probing a very small sample volume (ca. 90 nL). A significant portion of this thesis is devoted to demonstrating the powerful capabilities of CEAS, CRDS and BBCEAS in monitoring radical recombination reactions and associated magnetic field effects (MFEs) in solution. The efficacy of CEAS as a high-sensitivity MFE detection method has been established in a proof-of-principle study, using narrow band CEAS in combination with phase-sensitive detection: MFE-induced absorbance changes of ca. 10-6 could be detected using the modulated CEAS technique and the data are shown to be superior to those obtained using conventional transient absorption (TA) methods typically employed for MFE measurements. The powerful capabilities of CRDS in monitoring radical recombination reactions and associated MFEs are also demonstrated. In particular, a pump-probe CRDS variant allows not only high sensitivity (Amin on the order 10-6 ), but also sub-microsecond time-resolution. Combined, these features represent significant advantages over TA. Finally, SC-BBCEAS is used to measure full visible spectra of photoinduced reactions and their MFEs. The applicability of this approach to in vitro MFE studies of Drosophila cryptochrome is demonstrated—the results mark the first in vitro observation of a magnetic field response in an animal cryptochrome, a key result supporting the hypothesis that cryptochromes are involved in the magnetic sense in animals.- Published
- 2012
119. Spectroscopy and dynamics of metal clusters
- Author
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Hamilton, Suzanne M. and Mackenzie, Stuart R.
- Subjects
546.3 ,Laser Spectroscopy ,Computational chemistry ,Physical Sciences ,Mass spectrometry ,Chemistry & allied sciences ,Physical & theoretical chemistry ,Catalysis ,Surface chemistry - Abstract
A range of spectroscopic and computational techniques have been applied to the study of three metal cluster systems: vanadium monoxide, the Au2 molecule, and Rh
n N2 O+ clusters. A new instrument has been built for spectroscopy experiments on metal clusters, consisting of a laser ablation cluster source and a linear time-of-flight mass spectrometer. The instrument was characterised using nitric oxide spectroscopy and applied to the electronic REMPI spectrum of vanadium oxide in the visible region. The rotational constants and band origins of several known states have been determined, and the observation of a new spin-forbidden transition has been used to connect the energies of the quartet and doublet manifolds of VO. A new 32 Π state was also observed and characterised. The photoionisation and photodissociation of Au2 were then studied at 157 nm, and between 35500 and 37200 cm-1 with another new instrument recently constructed in the group. Excited and ground state Au photofragments were produced in both spectral regions, and have been detected and assigned using velocity map imaging. The 157 nm photodissociation produced gold atom products in the seven highest-energy accessible channels in a single-photon dissociation process. The complex near-UV spectrum involved two-photon excitation to two 0g + excited states close to their dissociation thresholds, followed by predissociation to thirteen different Au product channels. The branching ratios for dissociation into each of these channels varied across the spectrum as different dissociation limits and curve crossings occurred. The mid- and far-infrared multiple-photon dissociation spectra of Rhn N2 O+ clusters have been recorded using the argon-tagging action spectroscopy technique and free electron laser radiation. The results have been compared to density functional theory calculations to deduce the nature of the binding and the likely low-lying electronic and geometrical structures. The N2 O was found to be molecularly adsorbed on the surface of the cluster but, upon infrared heating of the complex via the N2 O vibrational modes, was observed to undergo a reaction, producing N2 and cluster oxides Rhn O+ . The reaction is believed to be thermal and mode-independent, but the efficiency of the surface reaction does vary with cluster size, with the n=5 cluster showing no detectable reaction.- Published
- 2011
120. The chemistry of nitrogen oxides on small size-selected cobalt clusters, Con+.
- Author
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Anderson, Marie L., Lacz, Agnieszka, Drewello, Thomas, Derrick, Peter J., Woodruff, D. Phil, and Mackenzie, Stuart R.
- Subjects
- *
FOURIER transforms , *ION cyclotron resonance spectrometry , *COBALT compounds , *NITROGEN oxides , *CHEMISORPTION , *CHEMICAL reactions , *CHEMICAL decomposition - Abstract
Fourier transform ion cyclotron resonance mass spectrometry has been employed to study the reactions of gas-phase cationic cobalt clusters, Con+ (n=4–30), with nitric oxide, NO, and nitrous oxide, N2O, under single collision conditions. Isolation of the initial cluster permits detailed investigation of fragmentation channels which characterize the reactions of all but the largest clusters studied. In reaction with N2O, most clusters generate the monoxides ConO+ without fragmentation, cobalt atom loss accompanying only subsequent reactions. By contrast, chemisorption of even a single NO molecule is accompanied by fragmentation of the cluster. The measured rate coefficients for the Con++N2O reaction as a function of cluster size are significantly smaller than those calculated using the surface charge capture model, while for NO the rates are comparable. The reactions have been studied under high coverage conditions by storing clusters for extended periods to permit multiple reactions to occur. This leads to interesting chemistry on the surface of the cluster resulting in the formation of stable oxide clusters and/or the decomposition of nitric oxide on the cluster with the resulting loss of molecular nitrogen. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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121. VUV photodissociation dynamics of diatomic gold, Au2: A velocity map imaging study at 157nm
- Author
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Hopkins, W. Scott, Hamilton, Suzanne M., McNaughter, Paul D., and Mackenzie, Stuart R.
- Subjects
- *
PHOTODISSOCIATION , *DIATOMS , *GOLD , *ATOMS , *ENERGY conservation , *PHOTOCHEMISTRY , *IONIZATION (Atomic physics) - Abstract
Abstract: The photodissociation dynamics of Au2 at 157nm have been studied by velocity map imaging. Fragmentation into seven of the nine energetically accessible channels has been observed with a high propensity for the formation of electronically excited fragment atoms. Fragmentation channels are assigned using total energy conservation and confirmed in two-colour experiments in which photolysis is followed by quantum state-selective resonance enhanced multi-photon ionization. The combination of one-and two-colour experiments permits the determination of relative branching ratios at 157nm for product channels correlating to Au 5d96s2(2D3/2) and Au 5d96s2(2D5/2) atomic fragments. [Copyright &y& Elsevier]
- Published
- 2009
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122. Atomic Cluster Au10+ Is a Strong Broadband Midinfrared Chromophore.
- Author
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Green, Alice E., Gentleman, Alexander S., Schöllkopf, Wieland, Fielicke, André, and Mackenzie, Stuart R.
- Subjects
- *
ATOMIC clusters , *MOLECULAR vibration , *ELECTRONIC excitation , *PHOTONS , *ABSORPTION - Abstract
We report an intense broadband midinfrared absorption band in the Au10+ cluster in a region in which only molecular vibrations would normally be expected. Observed in the infrared multiple photon dissociation spectra of Au10Ar+, Au10(N2O)+, and Au10(OCS)+, the smooth feature stretches 700-3400 cm-1 (λ=14-2.9 μm). Calculations confirm unusually low-energy allowed electronic excitations consistent with the observed spectra. In Au10(OCS)+, IR absorption throughout the band drives OCS decomposition resulting in CO loss, providing an alternative method of bond activation or breaking. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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123. A Combined Infrared and Computational Study of Gas-Phase Mixed-Ligand Rhodium Complexes: Rh(CO) n (N 2 O) m + ( n = 1-5, m = 1-4).
- Author
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Meizyte G, Brown RH, Brewer EI, Watson PD, and Mackenzie SR
- Abstract
In this study, mixed carbonyl and nitrous oxide complexes with Rh
+ were studied by mass-selective infrared photodissociation spectroscopy in a molecular beam. The infrared spectra, recorded in the region of the CO and N2 O N═N stretches, were assigned and interpreted with the aid of simulated spectra of low-energy structural isomers. Clear evidence of an inner coordination shell of four ligands is observed. The observed vibrational structure can be understood on the basis of local mode vibrations in the two ligands. However, there is also evidence of multiple low-lying isomers and cooperative binding effects between the two ligands. In particular, σ donation from directly coordinated nitrous oxide ligands drives more classical carbonyl bonding than has been observed in pure carbonyl complexes. The observed fragmentation branching ratios following resonant infrared absorption are explained by simple statistical and energetic arguments, providing a contrast with those of equivalent Au+ complexes.- Published
- 2023
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124. An infrared study of CO 2 activation by holmium ions, Ho + and HoO .
- Author
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Brewer EI, Green AE, Gentleman AS, Beardsmore PW, Pearcy PAJ, Meizyte G, Pickering J, and Mackenzie SR
- Abstract
We report a combined experimental and computational study of carbon dioxide activation at gas-phase Ho
+ and HoO+ centres. Infrared action spectra of Ho(CO2 )n + and [HoO(CO2 )n ]+ ion-molecule complexes have been recorded in the spectral region 1700-2400 cm-1 and assigned by comparison with simulated spectra of energetically low-lying structures determined by density functional theory. Little by way of activation is observed in Ho(CO2 )n + complexes with CO2 binding end-on to the Ho+ ion. By contrast, all [HoO(CO2 )n ]+ complexes n ≥ 3 show unambiguous evidence for formation of a carbonate radical anion moiety, . The signature of this structure, a new vibrational band observed around 1840 cm-1 for n = 3, continues to red-shift monotonically with each successive CO2 ligand binding with net charge transfer from the ligand rather than the metal centre.- Published
- 2022
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125. Infrared Study of OCS Binding and Size-Selective Reactivity with Gold Clusters, Au n + ( n = 1-10).
- Author
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Green AE, Schaller S, Meizyte G, Rhodes BJ, Kealy SP, Gentleman AS, Schöllkopf W, Fielicke A, and Mackenzie SR
- Abstract
OCS binding to and reactivity with isolated gold cluster cations, Au
n + ( n = 1-10), has been studied by infrared multiple photon dissociation (IR-MPD) spectroscopy in conjunction with quantum chemical calculations. The distribution of complexes Aun Sx (OCS)m + formed reflects the relative reactivity of different cluster sizes with OCS, under the multiple collision conditions of our ablation source. The IR-MPD spectra of Aun (OCS)+ ( n = 3-10) clusters are interpreted in terms of either μ1 or μ2 S binding motifs. Analysis of the fragmentation products following infrared excitation of parent Aun (OCS)+ clusters reveals strongly size-selective (odd-even) branching ratios for OCS and CO loss, respectively. CO loss signifies infrared-driven OCS decomposition on the cluster surface and is observed to occur predominantly on even n clusters (i.e., those with odd electron counts). The experimental data, including fragmentation branching ratios, are consistent with calculated potential energy landscapes, in which the initial species trapped are molecularly bound entrance channel complexes, rather than global minimum inserted structures. Attempts to generate Rhn (OCS)+ and Ptn (OCS)+ equivalents failed; only sulfide reaction products were observed in the mass spectrum, even after cooling the cluster source to -100 °C.- Published
- 2020
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126. Structural isomers and low-lying electronic states of gas-phase M + (N 2 O) n (M = Co, Rh, Ir) ion-molecule complexes.
- Author
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Cunningham EM, Gentleman AS, Beardsmore PW, and Mackenzie SR
- Abstract
The structures of gas-phase group nine cation-nitrous oxide metal-ligand complexes, M
+ (N2 O)n (M = Co, Rh, Ir; n = 2-7) have been determined by a combination of infrared photodissociation spectroscopy and density functional theory. The infrared spectra were recorded in the region of the N2 O asymmetric (N[double bond, length as m-dash]N) stretch using the inert messenger technique and show spectroscopically distinct features for N- and O-bound isomers. The evolution of the spectra with increasing ligand number is qualitatively different for each of the metal ions studied here with only Co+ (N2 O)n complexes behaving similarly to the coinage metal complexes studied previously. The rich variety of electronic and isomeric structures identified make these species attractive targets for infrared-driven, isomer selective intra-complex chemistry.- Published
- 2019
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127. Coulomb explosion imaging of CH 3 I and CH 2 ClI photodissociation dynamics.
- Author
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Allum F, Burt M, Amini K, Boll R, Köckert H, Olshin PK, Bari S, Bomme C, Brauße F, Cunha de Miranda B, Düsterer S, Erk B, Géléoc M, Geneaux R, Gentleman AS, Goldsztejn G, Guillemin R, Holland DMP, Ismail I, Johnsson P, Journel L, Küpper J, Lahl J, Lee JWL, Maclot S, Mackenzie SR, Manschwetus B, Mereshchenko AS, Mason R, Palaudoux J, Piancastelli MN, Penent F, Rompotis D, Rouzée A, Ruchon T, Rudenko A, Savelyev E, Simon M, Schirmel N, Stapelfeldt H, Techert S, Travnikova O, Trippel S, Underwood JG, Vallance C, Wiese J, Ziaee F, Brouard M, Marchenko T, and Rolles D
- Abstract
The photodissociation dynamics of CH
3 I and CH2 ClI 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 CH2 ClI 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.- Published
- 2018
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128. IR Signature of Size-Selective CO 2 Activation on Small Platinum Cluster Anions, Pt n - (n=4-7).
- Author
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Green AE, Justen J, Schöllkopf W, Gentleman AS, Fielicke A, and Mackenzie SR
- Abstract
Infrared multiple photon dissociation spectroscopy (IR-MPD) has been employed to determine the nature of CO
2 binding to size-selected platinum cluster anions, Ptn - (n=4-7). Interpreted in conjunction with density functional theory simulations, the results illustrate that the degree of CO2 activation can be controlled by the size of the metal cluster, with dissociative activation observed on all clusters n≥5. Of potential practical significance, in terms of the use of CO2 as a useful C1 feedstock, CO2 is observed molecularly-bound, but highly activated, on the Pt4 - cluster. It is trapped behind a barrier on the reactive potential energy surface which prevents dissociation., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)- Published
- 2018
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129. Infrared Signature of Structural Isomers of Gas-Phase M + (N 2 O) n (M = Cu, Ag, Au) Ion-Molecule Complexes.
- Author
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Cunningham EM, Gentleman AS, Beardsmore PW, Iskra A, and Mackenzie SR
- 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
+ (N2 O)n [M = Cu, Ag, Au; n = 2-7] complexes. The spectra provide clear evidence for both nitrogen- and oxygen-bound ligands giving rise to a wide range of structural isomers for each complex studied. The evolution of the complex structures observed as well as spectral trends for each metal center are interpreted in terms of a molecular orbital binding picture and resulting calculated ligand binding energies. Given the environmental importance of nitrogen oxides, these results have implications for metal-catalyzed removal of nitrous oxide and, particularly, the prospect of initiating infrared-driven isomer-selective chemistry in size-selected complexes.- Published
- 2017
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130. Infrared Spectroscopy of Gas-Phase M + (CO 2 ) n (M = Co, Rh, Ir) Ion-Molecule Complexes.
- Author
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Iskra A, Gentleman AS, Kartouzian A, Kent MJ, Sharp AP, and Mackenzie SR
- Abstract
The structures of gas-phase M
+ (CO2 )n (M = Co, Rh, Ir; n = 2-15) ion-molecule complexes have been investigated using a combination of infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy and density functional theory. The results provide insight into fundamental metal ion-CO2 interactions, highlighting the trends with increasing ligand number and with different group 9 ions. Spectra have been recorded in the region of the CO2 asymmetric stretch around 2350 cm-1 using the inert messenger technique and their interpretation has been aided by comparison with simulated infrared spectra of calculated low-energy isomeric structures. All vibrational bands in the smaller complexes are blue-shifted relative to the asymmetric stretch in free CO2 , consistent with direct binding to the metal center dominated by charge-quadrupole interactions. For all three metal ions, a core [M+ (CO2 )2 ] structure is identified to which subsequent ligands are less strongly bound. No evidence is observed in this size regime for complete activation or insertion reactions.- Published
- 2017
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131. Chemical amplification of magnetic field effects relevant to avian magnetoreception.
- Author
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Kattnig DR, Evans EW, Déjean V, Dodson CA, Wallace MI, Mackenzie SR, Timmel CR, and Hore PJ
- Subjects
- Animals, Ascorbic Acid chemistry, Flavins chemistry, Light, Muramidase chemistry, Tryptophan chemistry, Cryptochromes chemistry, Magnetic Fields, Sensory Receptor Cells physiology
- Abstract
Magnetic fields as weak as the Earth's can change the yields of radical pair reactions even though the energies involved are orders of magnitude smaller than the thermal energy, kBT, at room temperature. Proposed as the source of the light-dependent magnetic compass in migratory birds, the radical pair mechanism is thought to operate in cryptochrome flavoproteins in the retina. Here we demonstrate that the primary magnetic field effect on flavin photoreactions can be amplified chemically by slow radical termination reactions under conditions of continuous photoexcitation. The nature and origin of the amplification are revealed by studies of the intermolecular flavin-tryptophan and flavin-ascorbic acid photocycles and the closely related intramolecular flavin-tryptophan radical pair in cryptochrome. Amplification factors of up to 5.6 were observed for magnetic fields weaker than 1 mT. Substantial chemical amplification could have a significant impact on the viability of a cryptochrome-based magnetic compass sensor.
- Published
- 2016
- Full Text
- View/download PDF
132. Chemical reactivity on gas-phase metal clusters driven by blackbody infrared radiation.
- Author
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Parry IS, Kartouzian A, Hamilton SM, Balaj OP, Beyer MK, and Mackenzie SR
- Abstract
We report the observation of chemical reactions in gas-phase Rh(n)(N2O)m(+) complexes driven by absorption of blackbody radiation. The experiments are performed under collision-free conditions in a Fourier transform ion cyclotron resonance mass spectrometer. Mid-infrared absorption by the molecularly adsorbed N2O moieties promotes a small fraction of the cluster distribution sufficiently to drive the N2O decomposition reaction, leading to the production of cluster oxides and the release of molecular nitrogen. N2O decomposition competes with molecular desorption and the branching ratios for the two processes show marked size effects, reflecting variations in the relative barriers. The rate of decay is shown to scale approximately linearly with the number of infrared chromophores. The experimental findings are interpreted in terms of calculated infrared absorption rates assuming a sudden-death limit., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2015
- Full Text
- View/download PDF
133. Structures of platinum oxide clusters in the gas phase.
- Author
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Kerpal C, Harding DJ, Hermes AC, Meijer G, Mackenzie SR, and Fielicke A
- Subjects
- Gases chemistry, Molecular Structure, Photons, Quantum Theory, Spectrophotometry, Infrared, Oxides chemistry, Platinum chemistry
- Abstract
The structures of small gas-phase Pt(n)O(2m)(+) (n = 1-6, m = 1, 2) cluster cations have been investigated in a combined infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) study. On the basis of the infrared spectra obtained, it is concluded that in most clusters oxygen is bound dissociatively, preferring 2-fold bridge binding motifs, sometimes combined with singly coordinated terminal binding. Comparison of the oxide cluster structures with those of bare cationic platinum clusters reported previously reveals major structural changes induced in the platinum core upon oxygen binding. For some cluster sizes the presence of the Ar messenger atom(s) is found to induce a significant change in the observed cluster structure.
- Published
- 2013
- Full Text
- View/download PDF
134. Evanescent wave cavity ring-down spectroscopy (EW-CRDS) as a probe of macromolecule adsorption kinetics at functionalized interfaces.
- Author
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O'Connell MA, de Cuendias A, Gayet F, Shirley IM, Mackenzie SR, Haddleton DM, and Unwin PR
- Subjects
- Adsorption, Carboxylic Acids chemistry, Cellulose chemistry, Coumarins chemistry, Hydrogen-Ion Concentration, Kinetics, Polyglutamic Acid chemistry, Silicon Dioxide chemistry, Surface Properties, Macromolecular Substances chemistry, Spectrum Analysis
- Abstract
Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been employed to study the interfacial adsorption kinetics of coumarin-tagged macromolecules onto a range of functionalized planar surfaces. Such studies are valuable in designing polymers for complex systems where the degree of interaction between the polymer and surface needs to be tailored. Three tagged synthetic polymers with different functionalities are examined: poly(acrylic acid) (PAA), poly(3-sulfopropyl methacrylate, potassium salt) (PSPMA), and a mannose-modified glycopolymer. Adsorption transients at the silica/water interface are found to be characteristic for each polymer, and kinetics are deduced from the initial rates. The chemistry of the adsorption interfaces has been varied by, first, manipulation of silica surface chemistry via the bulk pH, followed by surfaces modified by poly(L-glutamic acid) (PGA) and cellulose, giving five chemically different surfaces. Complementary atomic force microscopy (AFM) imaging has been used for additional surface characterization of adsorbed layers and functionalized interfaces to allow adsorption rates to be interpreted more fully. Adsorption rates for PSPMA and the glycopolymer are seen to be highly surface sensitive, with significantly higher rates on cellulose-modified surfaces, whereas PAA shows a much smaller rate dependence on the nature of the adsorption surface.
- Published
- 2012
- Full Text
- View/download PDF
135. Communication: imaging wavefunctions in dissociative photoionization.
- Author
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Hopkins WS and Mackenzie SR
- Abstract
The dissociative ionization dynamics of excited electronic states of the xenon dimer, Xe(2), have been studied using velocity map ion imaging (VMI). A one-colour, (2+1) resonant excitation scheme was employed to first excite and then ionize selected vibrational levels of the Xe(2) 6p (2)[(1)∕(2)](0) 0(g)(+) Rydberg state. Cationic fragments were then detected by the VMI. The data provide an outstanding example of the reflection principle in photodissociation with the full nodal structure of the Rydberg state wavefunctions clearly observed in the final Xe(+) kinetic energy distributions without the need for scanning the excitation energy. Fitting of the observed distributions provides detailed and precise information on the form of the Xe(2)(+) I((1)/(2)g) potential energy curve involved which is in excellent agreement with the results of photoelectron imaging studies [Shubert and Pratt, J. Chem. Phys. 134, 044315 (2011)]. Furthermore, the anisotropy of the product angular distributions yields information on the evolution of the electronic character of the ionic state with internuclear separation, R. The combination of the nature of dissociative ionization and the extent of the bound state wavefunctions provide information over an unusually wide range of internuclear separation R (ΔR > 0.75 Å). This would normally require scanning over a considerable energy region but is obtained in these studies at a fixed excitation energy., (© 2011 American Institute of Physics)
- Published
- 2011
- Full Text
- View/download PDF
136. Kinetics of porphyrin adsorption and DNA-assisted desorption at the silica-water interface.
- Author
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Zhang M, Powell HV, Mackenzie SR, and Unwin PR
- Subjects
- Adsorption, Kinetics, Water, DNA chemistry, Porphyrins chemistry, Silicon Dioxide chemistry
- Abstract
Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been used to study in situ the kinetics of the adsorption of 5,10,15,20-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) from pH 7.4 phosphate buffer solution (PBS) to the silica-water interface and the interaction of calf thymus DNA (CT-DNA) with the resulting TMPyP-functionalized surface. TMPyP was delivered to the silica surface using an impinging jet technique to allow relatively fast surface kinetics to be accessed. Adsorption was first-order in TMPyP, and the initial adsorption rate constant at the bare surface was found to be k = (4.1 +/- 0.6) x 10(-2) cm s(-1). A deceleration in the adsorption kinetics was observed at longer times that could be described semiquantitatively using an Elovich-type kinetic expression. The limiting value of the absorbance corresponded approximately to monolayer coverage (6.2 x 10(13) molecules cm(-2)). Exposure of the TMPyP-modified silica surface to CT-DNA, achieved by flowing CT-DNA solution over the functionalized surface, resulted in efficient desorption of the TMPyP. The desorption process was driven by the interaction of TMPyP with CT-DNA, which UV-vis spectroscopy indicated involved intercalative binding. The desorption kinetics were also simulated using complementary finite element modeling of convection-diffusion coupled to a surface process.
- Published
- 2010
- Full Text
- View/download PDF
137. Following interfacial kinetics in real time using broadband evanescent wave cavity-enhanced absorption spectroscopy: a comparison of light-emitting diodes and supercontinuum sources.
- Author
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van der Sneppen L, Hancock G, Kaminski C, Laurila T, Mackenzie SR, Neil SR, Peverall R, Ritchie GA, Schnippering M, and Unwin PR
- Abstract
A white light-emitting diode (LED) with emission between 420 and 700 nm and a supercontinuum (SC) source with emission between 450 and 2500 nm have been compared for use in evanescent wave broadband cavity-enhanced absorption spectroscopy (EW-BB-CEAS). The method is calibrated using a dye with known absorbance. While the LED is more economic as an excitation source, the SC source is superior both in terms of baseline noise (noise equivalent absorbances lower than 10(-5) compared to 10(-4) absorbance units (a.u.)) and accuracy of the measurement; these baseline noise levels are comparable to evanescent wave cavity ringdown spectroscopy (EW-CRDS) studies while the accessible spectral region of EW-BB-CEAS is much larger (420-750 nm in this study, compared to several tens of nanometres for EW-CRDS). The improvements afforded by the use of an SC source in combination with a high sensitivity detector are demonstrated in the broadband detection of electrogenerated Ir(IV) complexes in a thin-layer electrochemical cell arrangement. Excellent signal to noise is achieved with 10 micros signal accumulation times at a repetition rate of 600 Hz, easily fast enough to follow, in real time, solution kinetics and interfacial processes.
- Published
- 2010
- Full Text
- View/download PDF
138. Evanescent wave cavity ring-down spectroscopy as a probe of interfacial adsorption: interaction of Tris(2,2'-bipyridine)ruthenium(II) with silica surfaces and polyelectrolyte films.
- Author
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Powell HV, Schnippering M, Mazurenka M, Macpherson JV, Mackenzie SR, and Unwin PR
- Abstract
Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been used to study the interaction of the tris(2,2'-bipyridine)ruthenium(II) complex, [Ru(bpy)(3)](2+), at both native silica surfaces and surfaces modified with polyelectrolyte films. Both poly-l-lysine (PLL) and PLL/poly-l-glutamic acid (PGA) bilayer functionalized interfaces have been studied. Concentration isotherms exhibit Langmuir-type adsorption behavior on both silica and PGA-terminated surfaces from which equilibrium constants have been derived. The pH-dependence of the [Ru(bpy)(3)](2+) adsorption to silica and the PLL/PGA film has also been investigated. For the latter substrate, the effective surface pK(a) of the acid groups was found to be 5.5. The effect of supporting electrolyte was also investigated and was shown to have a significant effect on the extent of [Ru(bpy)(3)](2+) adsorption. A thin-layer electrochemical cell arrangement, in which a working electrode was positioned just above the substrate, was used to change the solution pH in a controlled way via the potential-pulsed chronoamperometric oxidation of water. By measuring the optical absorption using EW-CRDS during such experiments, the desorption of [Ru(bpy)(3)](2+) from the surface has been monitored in real time. Experiments were carried out at different cell thicknesses and at various pulse durations. By combining data from the EW-CRDS experiments with fluorescence confocal laser scanning microscopy (CLSM) to determine the pH at the substrate surface, the pK(a) of the PLL/PGA film could be ascertained and was found to agree with the static pH isotherm measurements. These studies provide a platform for the further use of electrochemistry combined with EW-CRDS to investigate dynamic processes at interfaces.
- Published
- 2009
- Full Text
- View/download PDF
139. Evanescent wave cavity ring-down spectroscopy in a thin-layer electrochemical cell.
- Author
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Mazurenka M, Wilkins L, Macpherson JV, Unwin PR, and Mackenzie SR
- Abstract
The application of evanescent wave cavity ring-down spectroscopy (EW-CRDS) in monitoring electrogenerated species within a thin-layer electrochemical cell is demonstrated. In the proof-of-concept experiments described, ferricyanide, Fe(CN)6(3-), was produced by the transport-limited oxidation of ferrocyanide, Fe(CN)6(4-), in a thin-layer solution cell (25-250 microm) formed between an electrode and the hypotenuse of a fused-silica prism. The prism constituted one element of a high-finesse optical cavity arranged in a triangular ring geometry with light being totally internally reflected at the silica/solution interface. The cavity was pumped with the output (approximately 417 nm) of a single-mode external cavity diode laser, which was continuously scanned across the cavity modes. The presence of electrogenerated ferricyanide within the resulting evanescent field, beyond the optical interface, was detected by the enhanced loss of light trapped within the cavity, as measured by the characteristic cavity ring down. In this way, the EW-CRDS technique is sensitive to absorption in only the first few hundred nanometers of solution above the silica surface. The cavity ring-down response accompanying both cyclic voltammetric and step potential chronoamperometry experiments at a variety of electrode-surface distances is presented, and the results are shown to be well reproduced in modeling by finite element methods. The studies herein thus provide a foundation for further applications of EW-CRDS combined with electrochemistry.
- Published
- 2006
- Full Text
- View/download PDF
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