Fifty years of ion and neutral thermochemistry by mass spectrometry

pre-printOriginating with the appearance potentials for "positive rays", the ability of mass spectrometry to obtain quantitative information about the energetics of both ions and neutrals has evolved dramatically. About 50 years ago, many of the techniques that are now common place were first implemented, the interim has seen significant advances in both instrumentation and analysis tools. In this review, a short historical perspective of mass spectrometric approaches to ion and neutral thermochemistry is provided. Included are determinations of ionization and appearance energies, electron affinities, and dissociation energies. The latter are explored via techniques utilizing metastable decomposition, visible and vuv photodissociation, infrared photodissociation, collision-induced dissociation, and electron-induced dissociations, as well as applications of equilibrium methods and association processes. Although many of these techniques focus on ion thermochemistry, the ability to measure the thermodynamics of neutrals via mass spectrometric approaches is also highlighted

The bond energy of ReO+: Guided ion-beam and theoretical studies of the reaction of Re+ (7S) with O2

pre-printThe kinetic-energy dependence of the Re+ + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for ReO+ formation from ground state Re+ (7S) is unusual, exhibiting two endothermic features. The kinetic energy dependence for ReO+ formation is analyzed to determine D0(Re+-O) = 4.82 ± 0.05 eV, with the higher energy feature having a threshold 1.35 ± 0.28 eV higher in energy. This bond energy is consistent with much less precise values determined in the literature. Formation of ReO2 + is also observed with a pressure dependent cross section, establishing that it is formed in an exothermic reaction of ReO+ with O2. The nature of the bonding for ReO+ and ReO2 + is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. The ground state of ReO+ is identified as either 5 or 3, with the latter favored once estimates of spin-orbit splitting are included. Bond energies for ground state ReO+ are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are lower, although estimated spin-orbit corrections increase the latter close to experiment. Potential energy surfaces for the reaction of Re+ with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Re+ (7S) inserts into O2 by forming a Re+(O2) (5A) complex which can then couple with additional surfaces to form ground state ReO2 + (3B1). Several explanations for the unusual dual endothermic features are explored, with no unambiguous explanation being evident. As such, this heavy metal system provides a very interesting experimental phenomenon of both adiabatic and nonadiabatic behavior

Transition metal cluster ion chemistry

Journal ArticleThe reactivity and thermochemistry of ionic metal atoms and clusters has been explored using guided ion beam mass spectrometry. With this apparatus, cross sections of ion-molecule reactions can be measured from thermal energies to hundreds of eV. Application to metal cluster chemistry demonstrates its utility for elucidating reaction dynamics and mechanisms and for determining cluster binding energies and ligand binding energies for both ionic and neutral species. Early results compare the largely unreactive atomic Mn+ with the dimer Mn2+

Statistical modeling of sequential collision-induced dissociation thresholds

Journal ArticleThermochemistry determined from careful analysis of the energy dependence of cross sections for collision-induced dissociation (CID) reactions has primarily come from the primary dissociation channel. Higher order dissociations generally have thresholds measured to be higher than the thermodynamic limit because of the unknown internal and kinetic energy distributions of the primary products

Mechanism of proton exchange: guided ion beam studies of the reactions, H(H2O)n+ (n=1-4) + D2O and D(D 2O)n+ (n=1-4) + H2O

Journal ArticleReactions of protonated water clusters, H(H2O)n+ (n=1-4) with D2O and their "mirror" reactions, D(D2O)n+ (n=1-4) with H2O, are are studied using guided-ion beam mass spectrometry. Absolute reaction cross sections are determined as a function of collision energy from thermal energy to over 10 eV

Thermochemistry of the activation of N2 on iron cluster cations: guided ion beam studies of the reactions of Fen+ (n=1-19) with N2

Journal ArticleThe kinetic energy dependences of the reactions of Fen + (n=1-19) with N2 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-15 eV. In addition to collision-induced dissociation forming Fem + ions, which dominate the product spectra, a variety of FemN2+ and FemN+ product ions, where m<n, is observed

Methane activation by nickel cluster cations, Nin+ (n=2-16): reaction mechanisms and thermochemistry of cluster-CHx (x=0-3) complexes

Journal ArticleThe kinetic energy dependences of the reactions of Nin+ (n=2-16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-10 eV. The main products are hydride formation NinD1, dehydrogenation to form NinCD2 1 , and double dehydrogenation yielding NinC1

Methane activation by cobalt cluster cations, Con+ (n=2-16): reaction mechanisms and thermochemistry of cluster-CHx (x=0-3) complexes

Journal ArticleThe kinetic energy dependences of the reactions of Con + (n=2-16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-10 eV. The main products are hydride formation, ConD+, dehydrogenation to form ConCD2 +, and double dehydrogenation yielding ConC+

Guided ion beam studies of the reaction of Nin+ (n=2-16) with D2: nickel cluster-deuteride bond energies

Journal ArticleThe kinetic-energy dependences of the reactions of Nin+ (n=2-16) with D2 are studied in a guided ion beam tandem mass spectrometer. The products observed are NinD+ for all clusters and NinD2 + for n=5-16. Reactions for formation of NinD+ are observed to exhibit thresholds, whereas cross sections for formation of NinD2+ (n=5-16) exhibit no obvious barriers to reaction

Reaction of Cu+ with dimethoxyethane: competition between association and multiple dissociation channels

Journal ArticleThe reaction of Cu1 with dimethoxyethane (DXE) is studied using kinetic-energy dependent guided ion beam mass spectrometry. The bimolecular reaction forms an associative Cu1(DXE) complex that is long-lived and dissociates into several competitive channels: C4H9O2 11CuH, Cu1(C3H6O)1CH3OH, back to reactants, and other minor channels. The kinetic-energy dependences of the cross sections for the three largest product channels are interpreted with several different models (including rigorous phase space theory ) to yield 0 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the reactant ions, Doppler broadening, and dissociation lifetimes