manuel manard | University of California, Santa Barbara (original) (raw)

Papers by manuel manard

Research paper thumbnail of Collision-induced dissociation of MO + and MO 2 + (M = Ta and W): Metal oxide and dioxide cation bond energies

International Journal of Mass Spectrometry, 2011

P.B. Armentrout).

Research paper thumbnail of Differential mobility spectrometry/mass spectrometry: The design of a new mass spectrometer for real-time chemical analysis in the field

International Journal of Mass Spectrometry, 2010

16 Differential mobility spectrometry 17 Miniature ion funnel 18 a b s t r a c t

Research paper thumbnail of Chemical, Biological, and Explosive Sensors for Field Measurements

Description/Abstract Special Technologies Laboratory (STL) is developing handheld chemical, biolo... more Description/Abstract Special Technologies Laboratory (STL) is developing handheld chemical, biological, and explosive (CBE) detection systems and sensor motes for wireless networked field operations. The CBE sensors are capable of detecting and identifying ...

Research paper thumbnail of Ion Mobility Mass Spectrometry Direct Isotope Abundance Analysis

The nuclear forensics community is currently engaged in the analysis of illicit nuclear or radioa... more The nuclear forensics community is currently engaged in the analysis of illicit nuclear or radioactive material for the purposes of non-proliferations and attribution. One technique commonly employed for gathering nuclear forensics information is isotope analysis. At ...

Research paper thumbnail of Binding interactions of mono- and diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

ABSTRACT Temperature-dependent equilibrium methods were used to measure sequential association en... more ABSTRACT Temperature-dependent equilibrium methods were used to measure sequential association energies and entropies for the attachment of C2H4 and C3H6 ligands to ground-state Ag+(1S, 4d10) and Ag2+(2Σg, 4d20 σ(5s)1). Experimental bond dissociation energies (BDEs) of Ag+(C2H4)n are 32.2, 30.1, 13.6, 6.5 and 4.4 kcal/mol for n = 1–5, respectively, with the BDE of the sixth ligand estimated to be 3.3 kcal/mol. The BDEs of Ag2+(C2H4)n are 24.7, 22.5, 12.5, 7.7 and 2.9 kcal/mol for n = 1–5, respectively. The BDEs of Ag+(C3H6)n are 39.2, 32.9, 13.3, 7.0 and 3.0 kcal/mol and the BDEs of Ag2+(C3H6)n are 28.1, 25.8, 12.4, 9.3 and 4.2 kcal/mol for n = 1–5, respectively. A first solvation shell of four is observed for the attachment of both C2H4 and C3H6 ligands to both the Ag+ and Ag2+ core ions with all subsequent ligand additions taking place in the second solvation shell. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of all the observed Ag+ and Ag2+ clusters as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of Dissociation reactions of diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads... more Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads to both simple ligand addition and loss of neutral Ag to form ligated Ag+. Rate constants for the dissociation of Ag2+ via association of both ethene and propene have been measured. Experimental and theoretical analysis suggests that loss of a neutral Ag atom occurs upon addition of either the second ethene or first propene ligand to the Ag2+ ion. The measured rate constants exhibit a negative temperature dependence and relatively high reaction efficiency suggesting that the dissociation reactions are exothermic. Electronic structure calculations were preformed using density functional theory (DFT) at the B3LYP level in order to generate potential transition state structures for the dissociation reactions. Phase space theory (PST) was used to model the experimental rate data. Good agreement was found between experiment, DFT calculations and PST results for both systems. In both reactions, the negative temperature dependence is due to two factors: The reactions are only mildly exothermic and the product density of states increases more slowly with energy than the reactant density of states. The second factor is due to an atom being one of the products. No evidence for tight transition states was found for either reaction.

Research paper thumbnail of Binding interactions of mono- and diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

Temperature-dependent equilibrium methods were used to measure sequential association energies an... more Temperature-dependent equilibrium methods were used to measure sequential association energies and entropies for the attachment of C2H4 and C3H6 ligands to ground-state Ag+(1S, 4d10) and Ag2+(2[Sigma]g, 4d20 [sigma](5s)1). Experimental bond dissociation energies (BDEs) of Ag+(C2H4)n are 32.2, 30.1, 13.6, 6.5 and 4.4 kcal/mol for n = 1-5, respectively, with the BDE of the sixth ligand estimated to be 3.3 kcal/mol. The BDEs of Ag2+(C2H4)n are 24.7, 22.5, 12.5, 7.7 and 2.9 kcal/mol for n = 1-5, respectively. The BDEs of Ag+(C3H6)n are 39.2, 32.9, 13.3, 7.0 and 3.0 kcal/mol and the BDEs of Ag2+(C3H6)n are 28.1, 25.8, 12.4, 9.3 and 4.2 kcal/mol for n = 1-5, respectively. A first solvation shell of four is observed for the attachment of both C2H4 and C3H6 ligands to both the Ag+ and Ag2+ core ions with all subsequent ligand additions taking place in the second solvation shell. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of all the observed Ag+ and Ag2+ clusters as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of Origin of Bonding Interactions in Cu 2 + (H 2 ) n Clusters: An Experimental and Theoretical Investigation

Journal of Physical Chemistry A, 2002

... Manuel J. Manard, John E. Bushnell, Summer L. Bernstein, and Michael T. Bowers*. Department o... more ... Manuel J. Manard, John E. Bushnell, Summer L. Bernstein, and Michael T. Bowers*. Department of Chemistry, University of California, Santa Barbara, Santa Barbara, California 93106-9510. J. Phys. Chem. A , 2002, 106 (42), pp ...

Research paper thumbnail of Structures and ligand binding energies of size seleceted gold and silver clusters: Approach to the bulk

Gold and silver clusters are formed by laser ablation, mass selected, and either reacted with eth... more Gold and silver clusters are formed by laser ablation, mass selected, and either reacted with ethene or subjected to ion mobility measurement. Structures are assigned by two methods. In the first sequential ligand binding energies are measured and correlated with possible structures. In the second experimental cross sections are correlated with cross sections from model structures. Both anionic and cationic clusters are measured in the size range 3 to 13. For the anions calculated and experimental detachment energies are also used as structural diagnostics. The various data are compared with bulk values and approach to the bulk assessed.

Research paper thumbnail of An experimental and theoretical investigation into the binding interactions of silver cluster cations with ethene and propene

International Journal of Mass Spectrometry, 2006

Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C2H4... more Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C2H4 ligands to ground-state Agm+ (m = 3-13) clusters and for the attachment of C3H6 ligands to ground-state Agm+ (m = 3-9) clusters have been measured using temperature-dependent equilibrium methods. Variations in metal-ligand BDEs are examined in detail both as a function of sequential ligand addition to a given Agm+ cluster and as a function Agm+ cluster size for the first ligand additions. With the exception of the Ag6+ and Ag7+ clusters, BDEs for the loss of a ligand from the Agm+(L) (m = 3-13, L = C2H4; m = 3-9, L = C3H6) clusters decrease as the size of the silver clusters increase. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of the silver-alkene clusters of interest as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of An experimental and theoretical investigation into the binding interactions of silver cluster cations with ethene and propene

International Journal of Mass Spectrometry, 2006

ABSTRACT Sequential bond dissociation energies (BDEs) and association entropies for the attachmen... more ABSTRACT Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C2H4 ligands to ground-state Agm+ (m = 3-13) clusters and for the attachment of C3H6 ligands to ground-state Agm+ (m = 3-9) clusters have been measured using temperature-dependent equilibrium methods. Variations in metal-ligand BDEs are examined in detail both as a function of sequential ligand addition to a given Agm+ cluster and as a function Agm+ cluster size for the first ligand additions. With the exception of the Ag6+ and Ag7+ clusters, BDEs for the loss of a ligand from the Agm+(L) (m = 3-13, L = C2H4; m = 3-9, L = C3H6) clusters decrease as the size of the silver clusters increase. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of the silver-alkene clusters of interest as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of Bonding interactions in Ag +(O 2) n and Ag 2 +(O 2) n clusters: experiment and theory

International Journal of Mass Spectrometry, 2003

Equilibrium methods were used to measure binding energies and entropies for the attachment of up ... more Equilibrium methods were used to measure binding energies and entropies for the attachment of up to four O2 ligands to ground-state Ag+(1S, 4d10) and for the attachment of up to three O2 ligands to ground-state Ag2+(2Σg, 4d20 σ(5s)1). Bond dissociation energies (BDEs) of the first three O2 ligands from Ag+(O2)n are 6.9, 7.4, and 5.5kcal/mol for n=1–3, respectively, with the BDE of the fourth ligand estimated to be 4.8kcal/mol. BDEs of the first and second O2 ligands from Ag2+(O2)n are 4.5 and 4.2kcal/mol, respectively, with the BDE of the third ligand estimated to be 3.5kcal/mol. All of the observed attachments of O2 ligands to both the monomer and dimer Ag core ions were within the first solvation shell. Theoretical calculations at the DFT-B3LYP level were done on all of the observed Ag+ and Ag2+ clusters in order to determine the vibrational frequencies and geometries and to examine the origin of the bonding and its variation with core ion coordination. Comparisons are made with the Cu+(H2)n and Cu2+(H2)n systems.

Research paper thumbnail of Dissociation reactions of diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads... more Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads to both simple ligand addition and loss of neutral Ag to form ligated Ag+. Rate constants for the dissociation of Ag2+ via association of both ethene and propene have been measured. Experimental and theoretical analysis suggests that loss of a neutral Ag atom occurs upon addition of

Research paper thumbnail of Formation, deposition and examination of size selected metal clusters on semiconductor surfaces: An experimental setup

International Journal of Mass Spectrometry, 2006

An instrument designed to investigate the chemical behavior of size selected metal clusters on se... more An instrument designed to investigate the chemical behavior of size selected metal clusters on semiconductor surfaces is described. The clusters are formed using laser vaporization, mass selected in a magnetic mass analyzer and deposited on TiO 2 substrates under UHV conditions with impact energies ranging from ≤1 to >100 eV/atom. Intensities of mass selected Au n + and Ag n + clusters range from 0.03 to 3 nA. Intensity, beam focusing and deposition energy are discussed. Once deposited on the surface, the clusters are investigated using scanning tunneling microscopy (STM) and/or temperature programmed desorption (TPD). Examples are presented showing STM images of Au 5 deposited on a clean rutile titania surface and of the TPD of propene from TiO 2 .

Research paper thumbnail of Probing Shapes of Bichromophoric Metal−Organic Complexes Using Ion Mobility Mass Spectrometry

Journal of The American Chemical Society, 2005

Ion mobility mass spectrometry (IM-MS) was used to probe the structures of several metal complexe... more Ion mobility mass spectrometry (IM-MS) was used to probe the structures of several metal complexes carrying pendant chromophores. The three complexes investigated were the copper(II) complex Cu(DAC) 2+ (DAC ) 1,8-bis(9-methylanthracyl)cyclam, cyclam ) 1,4,8,11-tetraazacyclotetradecane), the N-nitrosylated ligand DAC-NO, and the Roussin's red salt ester (µ-S,µ-S′)-protoporphyrin-IX-bis(2-thioethyl ester)tetranitrosyldiiron (PPIX-RSE). From the IM-MS data coupled with theoretical calculations, it was found that [Cu II (DAC -H)] + exists as a single conformer, with one anthracenyl group above the cyclam and the other below, similar to the crystal structure of Cu II (DAC) 2+ . The metal-free N-nitrosylated ligand (DAC-NO + H) + has two conformations: one family of structures has one anthracenyl group above the cyclam and one below, while the other has both anthracenyl groups on the same side of the cyclam. These observations are consistent with 1 H NMR data for the neutral DAC-NO complex that indicate the presence of two geometric isomers in solution. The third species, PPIX-RSE, has a porphyrin chromophore covalently linked to an Fe 2S2(NO)4 cluster for use as a precursor for the photochemical delivery of nitric oxide in single-and two-photon excitation processes. Ion mobility indicates the presence of two (PPIX-RSE + H) + conformations, consistent with the previous interpretation of the bimodal fluorescence lifetime decay seen for PPIX-RSE. DFT structures, in good agreement with the IM-MS cross sections, indicate two "bent" conformations with the planes of the porphyrin and Fe2S2 rings at different angles with respect to each other.

Research paper thumbnail of Probing the Structure of Gas-Phase Metallic Clusters via Ligation Energetics: Sequential Addition of C 2 H 4 to Ag m + ( m = 3−7

Journal of The American Chemical Society, 2005

A new method that utilizes ligation to probe geometries of clusters in the gas-phase has been dev... more A new method that utilizes ligation to probe geometries of clusters in the gas-phase has been developed. This technique bases structural assignments on thermodynamic quantities obtained for sequential ligand additions to a bare cluster. The information is obtained from temperature-dependent equilibrium data. This method is also sensitive to changes in bare cluster conformations that occur as a result of ligand addition, and the results can be fine-tuned by choosing ligands that appropriately adjust cluster-ligand binding energies.

Research paper thumbnail of Structural Analysis of Metal Interactions with the Dinucleotide Duplex, dCG·dCG, Using Ion Mobility Mass Spectrometry

Journal of Physical Chemistry B, 2005

The metal binding properties of the dinucleotide duplex, dCG‚dCG, were analyzed in the gas phase ... more The metal binding properties of the dinucleotide duplex, dCG‚dCG, were analyzed in the gas phase with ion mobility mass spectrometry. Both MALDI and ESI were used to generate [M(dCG‚dCG)] + complexes. The collision cross section of each complex was measured in helium using ion mobility based methods and compared to calculated cross sections of theoretical structures. When metal cations classified as hard acids were combined with dCG‚dCG, the [M(dCG‚dCG)] + complex organized into a globular structure. However, when soft acid metal cations were examined, a structure was observed where the two C-G base pairs were Watson-Crick bound.

Research paper thumbnail of Collision-induced dissociation of MO + and MO 2 + (M = Ta and W): Metal oxide and dioxide cation bond energies

International Journal of Mass Spectrometry, 2011

P.B. Armentrout).

Research paper thumbnail of Differential mobility spectrometry/mass spectrometry: The design of a new mass spectrometer for real-time chemical analysis in the field

International Journal of Mass Spectrometry, 2010

16 Differential mobility spectrometry 17 Miniature ion funnel 18 a b s t r a c t

Research paper thumbnail of Chemical, Biological, and Explosive Sensors for Field Measurements

Description/Abstract Special Technologies Laboratory (STL) is developing handheld chemical, biolo... more Description/Abstract Special Technologies Laboratory (STL) is developing handheld chemical, biological, and explosive (CBE) detection systems and sensor motes for wireless networked field operations. The CBE sensors are capable of detecting and identifying ...

Research paper thumbnail of Ion Mobility Mass Spectrometry Direct Isotope Abundance Analysis

The nuclear forensics community is currently engaged in the analysis of illicit nuclear or radioa... more The nuclear forensics community is currently engaged in the analysis of illicit nuclear or radioactive material for the purposes of non-proliferations and attribution. One technique commonly employed for gathering nuclear forensics information is isotope analysis. At ...

Research paper thumbnail of Binding interactions of mono- and diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

ABSTRACT Temperature-dependent equilibrium methods were used to measure sequential association en... more ABSTRACT Temperature-dependent equilibrium methods were used to measure sequential association energies and entropies for the attachment of C2H4 and C3H6 ligands to ground-state Ag+(1S, 4d10) and Ag2+(2Σg, 4d20 σ(5s)1). Experimental bond dissociation energies (BDEs) of Ag+(C2H4)n are 32.2, 30.1, 13.6, 6.5 and 4.4 kcal/mol for n = 1–5, respectively, with the BDE of the sixth ligand estimated to be 3.3 kcal/mol. The BDEs of Ag2+(C2H4)n are 24.7, 22.5, 12.5, 7.7 and 2.9 kcal/mol for n = 1–5, respectively. The BDEs of Ag+(C3H6)n are 39.2, 32.9, 13.3, 7.0 and 3.0 kcal/mol and the BDEs of Ag2+(C3H6)n are 28.1, 25.8, 12.4, 9.3 and 4.2 kcal/mol for n = 1–5, respectively. A first solvation shell of four is observed for the attachment of both C2H4 and C3H6 ligands to both the Ag+ and Ag2+ core ions with all subsequent ligand additions taking place in the second solvation shell. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of all the observed Ag+ and Ag2+ clusters as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of Dissociation reactions of diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads... more Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads to both simple ligand addition and loss of neutral Ag to form ligated Ag+. Rate constants for the dissociation of Ag2+ via association of both ethene and propene have been measured. Experimental and theoretical analysis suggests that loss of a neutral Ag atom occurs upon addition of either the second ethene or first propene ligand to the Ag2+ ion. The measured rate constants exhibit a negative temperature dependence and relatively high reaction efficiency suggesting that the dissociation reactions are exothermic. Electronic structure calculations were preformed using density functional theory (DFT) at the B3LYP level in order to generate potential transition state structures for the dissociation reactions. Phase space theory (PST) was used to model the experimental rate data. Good agreement was found between experiment, DFT calculations and PST results for both systems. In both reactions, the negative temperature dependence is due to two factors: The reactions are only mildly exothermic and the product density of states increases more slowly with energy than the reactant density of states. The second factor is due to an atom being one of the products. No evidence for tight transition states was found for either reaction.

Research paper thumbnail of Binding interactions of mono- and diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

Temperature-dependent equilibrium methods were used to measure sequential association energies an... more Temperature-dependent equilibrium methods were used to measure sequential association energies and entropies for the attachment of C2H4 and C3H6 ligands to ground-state Ag+(1S, 4d10) and Ag2+(2[Sigma]g, 4d20 [sigma](5s)1). Experimental bond dissociation energies (BDEs) of Ag+(C2H4)n are 32.2, 30.1, 13.6, 6.5 and 4.4 kcal/mol for n = 1-5, respectively, with the BDE of the sixth ligand estimated to be 3.3 kcal/mol. The BDEs of Ag2+(C2H4)n are 24.7, 22.5, 12.5, 7.7 and 2.9 kcal/mol for n = 1-5, respectively. The BDEs of Ag+(C3H6)n are 39.2, 32.9, 13.3, 7.0 and 3.0 kcal/mol and the BDEs of Ag2+(C3H6)n are 28.1, 25.8, 12.4, 9.3 and 4.2 kcal/mol for n = 1-5, respectively. A first solvation shell of four is observed for the attachment of both C2H4 and C3H6 ligands to both the Ag+ and Ag2+ core ions with all subsequent ligand additions taking place in the second solvation shell. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of all the observed Ag+ and Ag2+ clusters as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of Origin of Bonding Interactions in Cu 2 + (H 2 ) n Clusters: An Experimental and Theoretical Investigation

Journal of Physical Chemistry A, 2002

... Manuel J. Manard, John E. Bushnell, Summer L. Bernstein, and Michael T. Bowers*. Department o... more ... Manuel J. Manard, John E. Bushnell, Summer L. Bernstein, and Michael T. Bowers*. Department of Chemistry, University of California, Santa Barbara, Santa Barbara, California 93106-9510. J. Phys. Chem. A , 2002, 106 (42), pp ...

Research paper thumbnail of Structures and ligand binding energies of size seleceted gold and silver clusters: Approach to the bulk

Gold and silver clusters are formed by laser ablation, mass selected, and either reacted with eth... more Gold and silver clusters are formed by laser ablation, mass selected, and either reacted with ethene or subjected to ion mobility measurement. Structures are assigned by two methods. In the first sequential ligand binding energies are measured and correlated with possible structures. In the second experimental cross sections are correlated with cross sections from model structures. Both anionic and cationic clusters are measured in the size range 3 to 13. For the anions calculated and experimental detachment energies are also used as structural diagnostics. The various data are compared with bulk values and approach to the bulk assessed.

Research paper thumbnail of An experimental and theoretical investigation into the binding interactions of silver cluster cations with ethene and propene

International Journal of Mass Spectrometry, 2006

Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C2H4... more Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C2H4 ligands to ground-state Agm+ (m = 3-13) clusters and for the attachment of C3H6 ligands to ground-state Agm+ (m = 3-9) clusters have been measured using temperature-dependent equilibrium methods. Variations in metal-ligand BDEs are examined in detail both as a function of sequential ligand addition to a given Agm+ cluster and as a function Agm+ cluster size for the first ligand additions. With the exception of the Ag6+ and Ag7+ clusters, BDEs for the loss of a ligand from the Agm+(L) (m = 3-13, L = C2H4; m = 3-9, L = C3H6) clusters decrease as the size of the silver clusters increase. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of the silver-alkene clusters of interest as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of An experimental and theoretical investigation into the binding interactions of silver cluster cations with ethene and propene

International Journal of Mass Spectrometry, 2006

ABSTRACT Sequential bond dissociation energies (BDEs) and association entropies for the attachmen... more ABSTRACT Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C2H4 ligands to ground-state Agm+ (m = 3-13) clusters and for the attachment of C3H6 ligands to ground-state Agm+ (m = 3-9) clusters have been measured using temperature-dependent equilibrium methods. Variations in metal-ligand BDEs are examined in detail both as a function of sequential ligand addition to a given Agm+ cluster and as a function Agm+ cluster size for the first ligand additions. With the exception of the Ag6+ and Ag7+ clusters, BDEs for the loss of a ligand from the Agm+(L) (m = 3-13, L = C2H4; m = 3-9, L = C3H6) clusters decrease as the size of the silver clusters increase. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of the silver-alkene clusters of interest as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Research paper thumbnail of Bonding interactions in Ag +(O 2) n and Ag 2 +(O 2) n clusters: experiment and theory

International Journal of Mass Spectrometry, 2003

Equilibrium methods were used to measure binding energies and entropies for the attachment of up ... more Equilibrium methods were used to measure binding energies and entropies for the attachment of up to four O2 ligands to ground-state Ag+(1S, 4d10) and for the attachment of up to three O2 ligands to ground-state Ag2+(2Σg, 4d20 σ(5s)1). Bond dissociation energies (BDEs) of the first three O2 ligands from Ag+(O2)n are 6.9, 7.4, and 5.5kcal/mol for n=1–3, respectively, with the BDE of the fourth ligand estimated to be 4.8kcal/mol. BDEs of the first and second O2 ligands from Ag2+(O2)n are 4.5 and 4.2kcal/mol, respectively, with the BDE of the third ligand estimated to be 3.5kcal/mol. All of the observed attachments of O2 ligands to both the monomer and dimer Ag core ions were within the first solvation shell. Theoretical calculations at the DFT-B3LYP level were done on all of the observed Ag+ and Ag2+ clusters in order to determine the vibrational frequencies and geometries and to examine the origin of the bonding and its variation with core ion coordination. Comparisons are made with the Cu+(H2)n and Cu2+(H2)n systems.

Research paper thumbnail of Dissociation reactions of diatomic silver cations with small alkenes: experiment and theory

International Journal of Mass Spectrometry, 2005

Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads... more Reaction of ground-state Ag2+ (2[Sigma]g+, 4d20 [sigma](5s)1) with either ethene or propene leads to both simple ligand addition and loss of neutral Ag to form ligated Ag+. Rate constants for the dissociation of Ag2+ via association of both ethene and propene have been measured. Experimental and theoretical analysis suggests that loss of a neutral Ag atom occurs upon addition of

Research paper thumbnail of Formation, deposition and examination of size selected metal clusters on semiconductor surfaces: An experimental setup

International Journal of Mass Spectrometry, 2006

An instrument designed to investigate the chemical behavior of size selected metal clusters on se... more An instrument designed to investigate the chemical behavior of size selected metal clusters on semiconductor surfaces is described. The clusters are formed using laser vaporization, mass selected in a magnetic mass analyzer and deposited on TiO 2 substrates under UHV conditions with impact energies ranging from ≤1 to >100 eV/atom. Intensities of mass selected Au n + and Ag n + clusters range from 0.03 to 3 nA. Intensity, beam focusing and deposition energy are discussed. Once deposited on the surface, the clusters are investigated using scanning tunneling microscopy (STM) and/or temperature programmed desorption (TPD). Examples are presented showing STM images of Au 5 deposited on a clean rutile titania surface and of the TPD of propene from TiO 2 .

Research paper thumbnail of Probing Shapes of Bichromophoric Metal−Organic Complexes Using Ion Mobility Mass Spectrometry

Journal of The American Chemical Society, 2005

Ion mobility mass spectrometry (IM-MS) was used to probe the structures of several metal complexe... more Ion mobility mass spectrometry (IM-MS) was used to probe the structures of several metal complexes carrying pendant chromophores. The three complexes investigated were the copper(II) complex Cu(DAC) 2+ (DAC ) 1,8-bis(9-methylanthracyl)cyclam, cyclam ) 1,4,8,11-tetraazacyclotetradecane), the N-nitrosylated ligand DAC-NO, and the Roussin's red salt ester (µ-S,µ-S′)-protoporphyrin-IX-bis(2-thioethyl ester)tetranitrosyldiiron (PPIX-RSE). From the IM-MS data coupled with theoretical calculations, it was found that [Cu II (DAC -H)] + exists as a single conformer, with one anthracenyl group above the cyclam and the other below, similar to the crystal structure of Cu II (DAC) 2+ . The metal-free N-nitrosylated ligand (DAC-NO + H) + has two conformations: one family of structures has one anthracenyl group above the cyclam and one below, while the other has both anthracenyl groups on the same side of the cyclam. These observations are consistent with 1 H NMR data for the neutral DAC-NO complex that indicate the presence of two geometric isomers in solution. The third species, PPIX-RSE, has a porphyrin chromophore covalently linked to an Fe 2S2(NO)4 cluster for use as a precursor for the photochemical delivery of nitric oxide in single-and two-photon excitation processes. Ion mobility indicates the presence of two (PPIX-RSE + H) + conformations, consistent with the previous interpretation of the bimodal fluorescence lifetime decay seen for PPIX-RSE. DFT structures, in good agreement with the IM-MS cross sections, indicate two "bent" conformations with the planes of the porphyrin and Fe2S2 rings at different angles with respect to each other.

Research paper thumbnail of Probing the Structure of Gas-Phase Metallic Clusters via Ligation Energetics: Sequential Addition of C 2 H 4 to Ag m + ( m = 3−7

Journal of The American Chemical Society, 2005

A new method that utilizes ligation to probe geometries of clusters in the gas-phase has been dev... more A new method that utilizes ligation to probe geometries of clusters in the gas-phase has been developed. This technique bases structural assignments on thermodynamic quantities obtained for sequential ligand additions to a bare cluster. The information is obtained from temperature-dependent equilibrium data. This method is also sensitive to changes in bare cluster conformations that occur as a result of ligand addition, and the results can be fine-tuned by choosing ligands that appropriately adjust cluster-ligand binding energies.

Research paper thumbnail of Structural Analysis of Metal Interactions with the Dinucleotide Duplex, dCG·dCG, Using Ion Mobility Mass Spectrometry

Journal of Physical Chemistry B, 2005

The metal binding properties of the dinucleotide duplex, dCG‚dCG, were analyzed in the gas phase ... more The metal binding properties of the dinucleotide duplex, dCG‚dCG, were analyzed in the gas phase with ion mobility mass spectrometry. Both MALDI and ESI were used to generate [M(dCG‚dCG)] + complexes. The collision cross section of each complex was measured in helium using ion mobility based methods and compared to calculated cross sections of theoretical structures. When metal cations classified as hard acids were combined with dCG‚dCG, the [M(dCG‚dCG)] + complex organized into a globular structure. However, when soft acid metal cations were examined, a structure was observed where the two C-G base pairs were Watson-Crick bound.