Guided-ion Beam Tandem Mass Spectrometry Research Articles

Enthalpy of the Cerium (Ce) Chemi-Ionization Reaction and CeO+, CeC+, and CeCO+ Bond Energies Determined by Energy-Resolved Guided Ion Beam Mass Spectrometry Experiments.

Cerium (Ce) oxide, carbide, and carbonyl cation bond energies and the exothermicity of the Ce chemi-ionization (CI) reaction with atomic oxygen were investigated using guided-ion beam tandem mass spectrometry (GIBMS). The kinetic energy dependent product cross sections for reactions of Ce+ with O2, CO, and CO2 and CeO+ with O2, CO, Xe, and Ar were measured using GIBMS. For the reactions of Ce+ with O2 and CO2, CeO+ is formed through an exothermic reaction, whereas CeO+ formation is endothermic in the reaction with CO. This reaction also forms CeC+ and CeCO+ is formed in the reaction of Ce+ with CO2, both in endothermic processes. Reactions of CeO+ with all four gases led to endothermic collision-induced dissociation as well as exchange reactions to form CeO2+ for the O2 and CO reactants. Bond dissociation energies (BDEs) at 0 K were determined through analyses of the kinetic energy dependent cross sections for all endothermic reactions. We determined that the BDEs of CeO+, CeC+, and CeCO+ are 8.46 ± 0.15, 3.93 ± 0.16, and ≥0.25 ± 0.07 eV, respectively, where the CeO+ BDE is a weighted average of 6 independent 0 K threshold measurements. The CeO+ BDE is combined with the ionization energy (IE) of Ce to determine an exothermicity of 2.91 ± 0.15 eV for the Ce + O → CeO+ + e- chemi-ionization reaction. Combined with neutral BDEs from the literature, the thermochemistry determined here also provides IE(CeO) = 5.03 ± 0.12 eV and IE(CeC) = 6.50 ± 0.16 eV. Theoretical calculations for ground and some excited states were performed for CeO+, CeC+, and CeCO+ to provide insight into the bonding and a comparison with the experimentally determined BDEs for each molecule.

Guided Ion Beam Studies of the Dy + O → DyO+ + e– Chemi-ionization Reaction Thermochemistry and Dysprosium Oxide, Carbide, Sulfide, Dioxide, and Sulfoxide Cation Bond Energies

Guided ion beam tandem mass spectrometry (GIBMS) was used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal dysprosium cation (Dy+) with O2, SO2, and CO and reactions of DyO+ with CO, O2, and Xe. DyO+ is formed through an exothermic process when Dy+ reacts with O2, whereas all other processes observed are found to be endothermic. The kinetic energy dependences of these cross sections were analyzed to yield 0 K bond dissociation energies (BDEs) for DyO+, DyC+, DyS+, DyO2+, and DySO+. The 0 K BDE for DyO+ is determined to be 5.60 ± 0.02 eV from the weighted average of six independent thresholds, which are dominated by the slightly endothermic reaction of Dy+ with SO2. Combined with the well-established Dy ionization energy (IE), this value indicates that the chemi-ionization reaction, Dy + O → DyO+ + e-, is endothermic by 0.33 ± 0.02 eV. Theoretical BDEs for Dy+-O, Dy+-C, Dy+-S, ODy+-O, and Dy+-SO were calculated at several levels of theory and basis sets for comparison with experiment with reasonable agreement achieved.

Singlet O2 Oxidation of the Radical Cation versus the Dehydrogenated Neutral Radical of 9-Methylguanine in a Watson-Crick Base Pair. Consequences of Structural Context.

In DNA, guanine is the most susceptible to oxidative damage by exogenously and endogenously produced electronically excited singlet oxygen (1O2). The reaction mechanism and the product outcome strongly depend on the nucleobase ionization state and structural context. Previously, exposure of a monomeric 9-methylguanine radical cation (9MG•+, a model guanosine compound) to 1O2 was found to result in the formation of an 8-peroxide as the initial product. The present work explores the 1O2 oxidation of 9MG•+ and its dehydrogenated neutral form [9MG - H]• within a Watson-Crick base pair consisting of one-electron-oxidized 9-methylguanine-1-methylcytosine [9MG·1MC]•+. Emphasis is placed on entangling the base pair structural context and intra-base pair proton transfer with and consequences thereof on the singlet oxygenation of guanine radical species. Electrospray ionization coupled with guided-ion beam tandem mass spectrometry was used to study the formation and reaction of guanine radical species in the gas phase. The 1O2 oxidation of both 9MG•+ and [9MG - H]• is exothermic and proceeds barrierlessly either in an isolated monomer or within a base pair. Single- and multi-referential theories were tested for treating spin contaminations and multi-configurations occurring in radical-1O2 interactions, and reaction potential energy surfaces were mapped out to support experimental findings. The work provides a comprehensive profile for the singlet oxygenation of guanine radicals in different charge states and in the absence and the presence of base pairing. All results point to an 8-peroxide as the major oxidation product in the experiment, and the oxidation becomes slightly more favorable in a neutral radical form. On the basis of a variety of reaction pathways and product profiles observed in the present and previous studies, the interplay between guanine structure, base pairing, and singlet oxygenation and its biological implications are discussed.

Activation of CO2 by Actinide Cations (Th+, U+, Pu+, and Am+) as Studied by Guided Ion Beam and Triple Quadrupole Mass Spectrometry.

Reactions of CO2 with Th+ have been studied using guided ion beam tandem mass spectrometry (GIBMS) and with An+ (An+ = Th+, U+, Pu+, and Am+) using triple quadrupole inductively coupled plasma mass spectrometry (QQQ-ICP-MS). Additionally, the reactions ThO+ + CO and ThO+ + CO2 were examined using GIBMS. Modeling the kinetic energy-dependent GIBMS data allowed the determination of bond dissociation energies (BDEs) for D0(Th+-O) and D0(OTh+-O) that are in reasonable agreement with previous GIBMS measurements. The QQQ-ICP-MS reactions were studied at higher pressures where multiple collisions between An+ and the neutral CO2 occur. As a consequence, both AnO+ and AnO2+ products were observed for all An+ except Am+, where only AmO+ was observed. The relative abundances of the observed monoxides compared to the dioxides are consistent with previous reports of the AnOn+ (n = 1, 2) BDEs. A comparison of the periodic trends of the group 4 transition metal, lanthanide (Ln), and actinide atomic cations in reactions with CO2 (a formally spin-forbidden reaction for most M+ ground states) and O2 (a spin-unrestricted reaction) indicates that spin conservation plays a minor role, if any, for the heavier Ln+ and An+ metals. Further correlation of Ln+ and An+ + CO2 reaction efficiencies with the promotion energy (Ep) to the first electronic state with two valence d-electrons (Ep(5d2) for Ln+ and Ep(6d2) for An+) indicates that the primary limitation in the activation of CO2 is the energetic cost to promote from the electronic ground state of the atomic metal ion to a reactive state.

Dynamically Hidden Reaction Paths in the Reaction of CF3 + + CO.

Reaction paths on a potential energy surface are widely used in quantum chemical studies of chemical reactions. The recently developed global reaction route mapping (GRRM) strategy automatically constructs a reaction route map, which provides a complete picture of the reaction. Here, we thoroughly investigate the correspondence between the reaction route map and the actual chemical reaction dynamics for the CF3+ + CO reaction studied by guided ion beam tandem mass spectrometry (GIBMS). In our experiments, FCO+, CF2+, and CF+ product ions were observed, whereas if the collision partner is N2, only CF2+ is observed. Interestingly, for reaction with CO, GRRM-predicted reaction paths leading to the CF+ + F2CO product channel are found at a barrier height of about 2.5 eV, whereas the experimentally obtained threshold for CF+ formation was 7.48 ± 0.15 eV. In other words, the ion was not obviously observed in the GIBMS experiment, unless a much higher collision energy than the requisite energy threshold was provided. On-the-fly molecular dynamics simulations revealed a mechanism that hides these reaction paths, in which a non-statistical energy distribution at the first collisionally reached transition state prevents the reaction from proceeding along some reaction paths. Our results highlight the existence of dynamically hidden reaction paths that may be inaccessible in experiments at specific energies and hence the importance of reaction dynamics in controlling the destinations of chemical reactions.

Structures, proton transfer and dissociation of hydroxylammonium nitrate (HAN) revealed by electrospray ionization tandem mass spectrometry and molecular dynamics simulations.

Hydroxylammonium nitrate (HAN) is a potential propellant candidate for dual-mode propulsion systems that combine chemical and electrospray thrust capabilities for spacecraft applications. However, the electrospray dynamics of HAN is currently not well understood. Capitalizing on electrospray ionization guided-ion beam tandem mass spectrometry and collision-induced dissociation measurements, and augmented by extensive molecular dynamics simulations, this work characterized the structures and reaction dynamics of the species present in the electrosprays of HAN under different conditions, which mimic those possibly occurring in low earth orbit and outer space. While being ionic in nature, the HAN monomer, however, adopts a stable covalent structure HONH2·HNO3 in the gas phase. Spontaneous proton transfer between the HONH2 and HNO3 moieties within the HAN monomer can be induced in the presence of a NO3-, a water ligand or a second HAN monomer within 3-5 Å or a H+ within 8 Å, regardless of their collision impact parameters. These facts imply that HAN proton transfer is trigged by a charge and/or a dipole of the collision partner without the need of chemical interaction or physical contact. Moreover, the addition of NO3- to HAN leads to the formation of a stable -O3N·HONH3+·NO3- anion in negative electrosprays. In contrast, when a proton approaches the HONH2·HNO3 structure, dissociative reactions occur that lead to the H2O, NO2 and HONH2 fragments (and their cations) but not intact HAN species in positive electrosprays.

Singlet O2 Reactions with Radical Cations of 8-Bromoguanine and 8-Bromoguanosine: Guided-Ion Beam Mass Spectrometric Measurements and Theoretical Treatments.

8-Bromoguanosine is generated in vivo as a biomarker for early inflammation. Its formation and secondary reactions lead to a variety of biological sequelae at inflammation sites, most of which are mutagenic and linked to cancer. Herein, we report the formation of radical cations of 8-bromoguanine (8BrG•+) and 8-bromoguanosine (8BrGuo•+) and their reactions toward the lowest excited singlet molecular oxygen (1O2)─a common reactive oxygen species generated in biological systems. This work aims to investigate synergistic, oxidatively generated damage of 8-brominated guanine and guanosine that may occur upon ionizing radiation, one-electron oxidation, and 1O2 oxidation. Capitalizing on measurements of reaction product ions and cross sections of 8BrG•+ and 8BrGuo•+ with 1O2 using guided-ion beam tandem mass spectrometry and augmented by computational modeling of the prototype reaction system, 8BrG•+ + 1O2, using the approximately spin-projected ωB97XD/6-31+G(d,p) density functional theory, the coupled cluster DLPNO-CCSD(T)/aug-cc-pVTZ and the multireference CASPT2(21,15)/6-31G**, probable reaction products, and potential energy surfaces (PESs) were mapped out. 8BrG•+ and 8BrGuo•+ present similar exothermic oxidation products, and their reaction efficiencies with 1O2 increase with decreasing collision energy. Both single- and multireference theories predicted that the two most energetically favorable reaction pathways correspond to 1O2-addition to the C8 and C5-positions of 8BrG•+, respectively. The CASPT2-calculated PES represents the best quantitative agreement with the experimental benchmark, in that the oxidation exothermicity is close to the water hydration energy of product ions and, thus, is able to eliminate a water ligand in the product ions.

Holmium (Ho) oxide, carbide, and dioxide cation bond energies and evaluation of the Ho + O → HoO+ + e- chemi-ionization reaction enthalpy.

Guided ion beam tandem mass spectrometry (GIBMS) and quantum chemical calculations are employed to evaluate the title chemi-ionization reaction with holmium. Exchange reactions of Ho+ with O2, CO, and SO2 and HoO+ with CO, as well as collision-induced dissociation (CID) reactions of HoO+ with Xe, O2, and CO, were performed using GIBMS. Formation of HoO+ is exothermic in reactions with O2 and SO2 but endothermic for reaction with CO, as is the exchange reaction of HoO+ with CO. Quantitative analysis of these reactions and the three CID reactions provides a robust method to determine the bond dissociation energy (BDE) of Ho+-O, 6.02 ± 0.13eV. BDEs for Ho+-C and OHo+-O are also measured as 2.27 ± 0.19 and 2.70 ± 0.27eV, respectively. All three measurements are the first direct determinations of these BDEs. By combining the BDE of HoO+ with the well-established ionization energy of Ho, the exothermicity of Ho in the title chemi-ionization reaction can also be obtained as 0.00 ± 0.13eV. All experimental thermochemistry was then compared to quantum chemical calculations for the purpose of establishing benchmarks and validation. BDEs determined via these calculations are in agreement with the experiment within the inherent experimental and theoretical uncertainties, with results obtained at the coupled-cluster with single, double, and perturbative triple excitations, CCSD(T), using all-electron basis sets yielding the most accurate results.

Energetics and mechanisms for decomposition of cationized amino acids and peptides explored using guided ion beam tandem mass spectrometry.

Fragmentation studies of cationized amino acids and small peptides as studied using guided ion beam tandem mass spectrometry (GIBMS) are reviewed. After a brief examination of the key attributes of the GIBMS approach, results for a variety of systems are examined, compared, and contrasted. Cationization of amino acids, diglycine, and triglycine with alkali cations generally leads to dissociations in which the intact biomolecule is lost. Exceptions include most lithiated species as well as a few examples for sodiated and one example for potassiated species. Like the lithiated species, cationization by protons leads to numerous dissociation channels. Results for protonated glycine, cysteine, asparagine, diglycine, and a series of tripeptides are reviewed, along with the thermodynamic consequences that can be gleaned. Finally, the important physiological process of the deamidation of asparagine (Asn) residues is explored by the comparison of five dipeptides in which the C-terminal partner (AsnXxx) is altered. The GIBMS thermochemistry is shown to correlate well with kinetic results from solution phase studies.

Relative Energetics of the Gas Phase Protomers of p-Aminobenzoic Acid and the Effect of Protonation Site on Fragmentation.

Guided ion beam tandem mass spectrometry (GIBMS) is used to investigate the energy-dependent threshold collision-induced dissociation (TCID) of the two protonated isomers (protomers) of p-aminobenzoic acid (p-ABA). The O-protomer of p-ABA (protonated at the carbonyl oxygen) was generated via electrospray ionization (ESI) from a methanol/water solution, whereas the N-protomer (protonated at the amine) was produced via ESI from an acetonitrile/water solution. The two protomers are clearly distinguishable from differences in the onsets of the fragmentation channels and in the abundance and identity of the products observed. Additional GIBMS experiments were performed on protonated benzoic acid (BA) and aniline, which serve as simple models for fragmentation driven by protonation at the carbonyl or amine group of p-ABA and provide insights into the dissociation channels of the two p-ABA protomers. Theoretical calculations were carried out to determine the dissociation mechanisms and for comparison with the experimental thermochemistry, which is obtained from modeling the kinetic energy dependent TCID cross sections after accounting for multiple collisions, kinetic shifts, competition between channels, and sequential dissociations. Calculations together with the energy-resolved experiments show that a product ion (C5H5+, m/z 65) common to both p-ABA protomers is produced from sequential dissociations via two different mechanisms. Furthermore, we demonstrate here that the relative stabilities of the two p-ABA protomers can be determined directly from experiment via shared product channels for which there are no barriers exceeding their asymptotic energies. Our results indicate that the two p-ABA protomers are nearly isoenergetic in the gas phase with a relative energy of 0.01 ± 0.26 eV favoring the O-protomer over the N-protomer. This result is in good agreement with calculations at the MP2 and CCSD(T) levels of theory.

Experimental and theoretical assessment of protonated Hoogsteen 9-methylguanine-1-methylcytosine base-pair dissociation: kinetics within a statistical reaction framework.

We investigated the collision-induced dissociation (CID) reactions of a protonated Hoogsteen 9-methylguanine-1-methylcytosine base pair (HG-[9MG·1MC + H]+), which aims to address the mystery of the literature reported "anomaly" in product ion distributions and compare the kinetics of a Hoogsteen base pair with its Watson-Crick isomer WC-[9MG·1MC + H]+ (reported recently by Sun et al.; Phys. Chem. Chem. Phys., 2020, 22, 24986). Product ion cross sections and branching ratios were measured as a function of center-of-mass collision energy using guided-ion beam tandem mass spectrometry, from which base-pair dissociation energies were determined. Product structures and energetics were assessed using various theories, of which the composite DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97XD/6-311++G(d,p) was adopted as the best-performing method for constructing a reaction potential energy surface. The statistical Rice-Ramsperger-Kassel-Marcus theory was found to provide a useful framework for rationalizing the dominating abundance of [1MC + H]+ over [9MG + H]+ in the fragment ions of HG-[9MG·1MC + H]+. The kinetics analysis proved the necessity for incorporating into kinetics modeling not only the static properties of reaction minima and transition states but more importantly, the kinetics of individual base-pair conformers that have formed in collisional activation. The analysis also pinpointed the origin of the statistical kinetics of HG-[9MG·1MC + H]+vs. the non-statistical behavior of WC-[9MG·1MC + H]+ in terms of their distinctively different intra-base-pair hydrogen-bonds and consequently the absence of proton transfer between the N1 position of 9MG and the N3' of 1MC in the Hoogsteen base pair. Finally, the Hoogsteen base pair was examined in the presence of a water ligand, i.e., HG-[9MG·1MC + H]+·H2O. Besides the same type of base-pair dissociation as detected in dry HG-[9MG·1MC + H]+, secondary methanol elimination was observed via the SN2 reaction of water with nucleobase methyl groups.

Activation of CO2 by Gadolinium Cation (Gd+): Energetics and Mechanism from Experiment and Theory

The exothermic and barrierless activation of CO2 by the lanthanide gadolinium cation (Gd+) to form GdO+ and CO is investigated in detail using guided ion beam tandem mass spectrometry (GIBMS) and theory. Kinetic energy dependent product ion cross sections from collision-induced dissociation (CID) experiments of GdCO2 + are measured to determine the energetics of OGd+(CO) and Gd+(OCO) intermediates. Modeling these cross sections yields bond dissociation energies (BDEs) for OGd+–CO and Gd+–OCO of 0.57 ± 0.05 and 0.38 ± 0.05 eV, respectively. The OGd+–CO BDE is similar to that previously measured for Gd+–CO, which can be attributed to the comparable electrostatic interaction with CO in both complexes. The Gd+(OCO) adduct is identified from calculations to correspond to an electronically excited state. The thermochemistry here and the recently measured GdO+ BDE allows for the potential energy surface (PES) of the Gd+ reaction with CO2 to be deduced from experiment in some detail. Theoretical calculations are performed for comparison with the experimental thermochemistry and for insight into the electronic states of the GdCO2 + intermediates, transition states, and the reaction mechanism. Although the reaction between ground state Gd+ (10D) and CO2 (1Σg +) reactants to form ground state GdO+ (8Σ−) and CO (1Σ+) products is formally spin-forbidden, calculations indicate that there are octet and dectet surfaces having a small energy gap in the entrance channel, such that they can readily mix. Thereby, the reaction can efficiently proceed along the lowest energy octet surface to yield ground state products, consistent with the experimental observations of an efficient, barrierless process. At high collision energies, the measured GdO+ cross section from the Gd+ reaction with CO2 exhibits a distinct feature, attributed to formation of electronically excited GdO+ products along a single dectet PES in a diabatic and spin-allowed process. Modeling this high-energy feature gives an excitation energy of 3.25 ± 0.16 eV relative to the GdO+ (8Σ−) ground state, in good agreement with calculated excitation energies for GdO+ (10Π, 10Σ−) electronic states. The reactivity of Gd+ with CO2 is compared with the group 3 transition metal cations and other lanthanide cations and periodic trends are discussed.

Cross sections and transport properties for Na+ in (DXE) gas

In this work we select most probable reactions of alkali metal ion Na+ with dimethoxyethane (DXE) molecule. Appropriate gas phase enthalpies of formation for the products were used to calculate scattering cross section as a function of kinetic energy with Denpoh-Nanbu theory. Calculated cross sections were compared with existing experimental results obtained by guided ion beam tandem mass spectrometry. Three body association reactions of ions with DXE is studied and compared to experimental results. Calculated cross sections were used to obtain transport parameters for alkali metal ion in DXE gas.

Energy-Resolved Collision-Induced Dissociation Studies of 2,2'-Bipyridine Complexes of the Late First-Row Divalent Transition-Metal Cations: Determination of the Third-Sequential Binding Energies.

The third-sequential binding energies of the late first-row divalent transition-metal cations with 2,2'-bipyridine (Bpy) are determined using guided-ion-beam tandem mass spectrometry (GIBMS) techniques. The metal cations investigated include the late first-row divalent transition-metal cations, Fe2+ , Co2+ , Ni2+ , Cu2+ , and Zn2+ . The kinetic-energy-dependent cross sections for collision-induced dissociation (CID) of the M2+ (Bpy)3 complexes are analyzed to extract absolute 0 and 298 K bond dissociation energies (BDEs) for the loss of an intact Bpy ligand. Theoretical electronic structure calculations at the B3LYP, BHandHLYP, and M06 levels of theory are performed to determine stable geometries and sequential BDEs of the M2+ (Bpy)x complexes (x=1-3). BDEs computed using the M06 functional are the largest, BHandHLYP values are intermediate, whereas B3LYP produces the smallest values. Very good agreement between the B3LYP theoretically calculated and threshold collision-induced dissociation experimentally determined BDEs is found, which suggests that the B3LYP functional is capable of accurately describing the binding in these M2+ (Bpy)3 complexes. Periodic trends in the binding of the M2+ (Bpy)x complexes are examined and compared to the analogous complexes with 1,10-phenanthroline (Phen), M2+ (Phen)x . Comparisons are also made to the analogous Bpy complexes, M+ (Bpy)x , with the late first-row monovalent transition-metal cations, Co+ , Ni+ , Cu+ , and Zn+ investigated previously.

Multiply charged gas-phase NaAOT reverse micelles: Formation, encapsulation of glycine, and collision-induced dissociation

We report a study of the generation and characterization of multiply charged, sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) aggregates in the gas phase, using electrospray ionization (ESI) guided-ion beam tandem mass spectrometry. It was found that distributions of gas-phase NaAOT aggregate size and charge are related to the surfactant states in electrosprayed solutions. ESI mass spectra of NaAOT/water/hexane reverse micellar solutions show the compositions of [(NaAOT) n Na z ] z+ , with the aggregation number ( n) and charge ( z) increase with increasing water content in solution. In contrast, gas-phase aggregates from NaAOT monomers in solution have smaller aggregation numbers and lower charges. Gas-phase NaAOT aggregates of n ≥ 13 could encapsulate one glycine molecule, and those of n ≥ 16 could encapsulate two glycine molecules. Up to five glycine molecules could be accommodated in single aggregates of n ≥ 24. Regardless of glycine encapsulation, no water molecules were detected within gas-phase NaAOT aggregates. Collision-induced dissociation (CID) was studied for mass-selected NaAOT aggregates with Xe, including measurements of product ion masses and CID cross-sections for both empty and glycine-encapsulating aggregates over the center-of-mass collision energy range of 0.1–8.0 eV. CID results provide a detailed probe of aggregate structures as well as the interactions between surfactants and the encapsulated glycine molecules. Specifically, the dependence of glycine encapsulation on aggregate size is observed in CID product ion mass spectra, too. The present study demonstrates that NaAOT surfactants are able to form reverse micelles in the gas phase, and gas-phase reverse micelles can act as nanometer-sized vehicles for transport of non-volatile biomolecules.

Size-Dependent Reaction Cross Section of Protonated Water Clusters H+(H2O)n (n = 2−11) with D2O

Collisional dynamics of size- and translational-energy-selected protonated water clusters H+(H2O)n (n = 2−11) in single collisions with D2O were investigated using guided-ion beam tandem mass spectrometry. The dominant reaction channel for the collision involves the incorporation of D2O into H+(H2O)n at low collision energy, whereas at high collision energy, the dissociation of H+(H2O)n is predominant. The measured total reaction cross section of H+(H2O)n with D2O is found to depend strongly on the cluster size; the cross section drastically increases as the cluster size increases from n = 4 to 5, 6 to 7, and 8 to 9 and has local minima at n = 6 and 8 at collision energies of 0.05 and 0.10 eV, respectively. The size dependence of the total cross section is discussed herein in terms of a comparison with the collision cross section obtained from ab initio calculations.

Incorporation probability of a water molecule into a water cluster

Abstract The cross-sections for incorporation of D 2 O into size- and energy-selected water cluster ions H + (H 2 O) n ( n =2–9) were experimentally measured under single-collision conditions using guided-ion beam tandem mass spectrometry. After estimation of the collision cross-section, the reaction probability for incorporation of D 2 O into H + (H 2 O) n was investigated as a function of the collision energy. The reaction probability for incorporation was found to be equal to unity at low collision energy by using the experimental data and theoretical curve derived from our model related to the recoil energy of the incident molecule. We examined, by calculation, the temperature dependence of the probability of the incorporation of H 2 O into neutral water clusters (H 2 O) n .

Collisional reaction of water cluster cations (H 2O) n+ ( n=2 and 3) with D 2O

Collisional reactions of size- and energy-selected unprotonated water clusters (H 2O) n + ( n=2 and 3) in a single-collision with D 2O were investigated at very low collision energy ranging from 0.05 to 2.0 eV using guided-ion beam tandem mass spectrometry. First, in the unimolecular and collision-induced dissociations of (H 2O) 2 + and (H 2O) 3 +, only the H 2O + fragment, but not the H 3O + fragment, was observed. These results suggest that the structure of (H 2O) 2 + is primarily hemibonded ‘(H 2O⋯OH 2) +’ rather than proton-transferred ‘(H 3O +⋯OH)’. Second, the measured incorporation cross-section of (H 2O) 2 + was found to be smaller than that of H +(H 2O) 2. From the dipole moment obtained by ab initio calculation, we found that the small values of the incorporation cross-section for (H 2O) 2 + were caused by the small value, 0.0 debye, of the dipole moment of the cluster.

Sequential bond energies of Pt +(NH 3) x ( x=1–4) determined by collision-induced dissociation and theory

The sequential bond energies of Pt +(NH 3) x ( x=1–4) are determined by collision-induced dissociation (CID) with Xe using guided-ion beam tandem mass spectrometry. Analysis of the kinetic energy-dependent cross sections includes consideration of multiple ion–neutral collisions, the internal energies of the complexes, and the dissociation lifetimes. We obtain the following 0 K bond energies in eV (kJ/mol): 2.84±0.12 (274±12), 2.71±0.10 (261±10), 0.80±0.05 (77±5), and 0.48±0.04 (46±4) for (NH 3) x−1 Pt +NH 3 with x=1–4, respectively. These values are in reasonable agreement with results of density functional ab initio calculations performed here. The trend in these bond energies is compared with those of platinum carbonyl cations and nickel ammonia cation complexes and discussed in terms of sdσ-hybridization, electrostatic interactions, and ligand–ligand steric interactions.

Sequential Bond Energies of Pt(CO)x+ (x = 1 −4) Determined by Collision-Induced Dissociation

The sequential bond energies of Pt(CO)x+ (x = 1−4) are determined by collision-induced dissociation with Xe using guided-ion beam tandem mass spectrometry. Analysis of the kinetic energy dependent cross sections yields 0 K bond energies in eV (kJ/mol) of 2.20 ± 0.10 (212 ± 10), 2.00 ± 0.10 (193 ± 10), 1.02 ± 0.05 (98 ± 5), and 0.55 ± 0.05 (53 ± 5) for (CO)x-1Pt+−CO with x = 1−4, respectively. These values are in reasonable agreement with results of density functional ab initio calculations in the literature. D0(Pt+−Xe) is determined as 0.86 ± 0.30 eV (83 ± 29 kJ/mol) from analysis of the ligand exchange reaction with PtCO+. The trend in these bond energies is compared with those of nickel and sodium carbonyl cations and discussed in terms of sdσ hybridization, electrostatic interactions, and ligand−ligand steric interactions.