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

Methane Adducts of Gold Dimer Cations: Thermochemistry and Structure from Collision-Induced Dissociation and Association Kinetics

The bond dissociation energies at 0 K (BDE) of Au₂⁺-CH₄ and Au₂CH₄⁺-CH₄ have been determined using two separate experimental methods. Analyses of collision-induced dissociation cross sections for Au₂CH₄⁺ + Xe and Au₂(CH₄)₂⁺ + Xe measured using a guided ion beam tandem mass spectrometer (GIBMS) yield BDEs of 0.71 ± 0.05 and 0.57 ± 0.07 eV, respectively. Statistical modeling of association kinetics of Au₂(CH₄)_0-2⁺ + CH₄ + He measured from 200 to 400 K and at 0.3-0.9 Torr using a selected-ion flow tube (SIFT) apparatus yields slightly higher values of 0.81 ± 0.21 and 0.75 ± 0.25 eV. The SIFT data also place a lower limit on the BDE of Au₂C₂H₈⁺-CH₄ of 0.35 eV, likely an activated isomer, not Au₂(CH₄)₂⁺-CH₄. Particular emphasis is placed on determining the uncertainty in the derivation from association kinetics measurements, including uncertainties in collisional energy transfer, calculated harmonic frequencies, and possible contribution of isomerization of the association complexes. This evaluation indicates that an uncertainty of ±0.2 eV should be expected and that an uncertainty of better than ±0.1 eV is unlikely to be reasonable.

Role of Chemical Dynamics Simulations in Mass Spectrometry Studies of Collision-Induced Dissociation and Collisions of Biological Ions with Organic Surfaces

In this article, a perspective is given of chemical dynamics simulations of collisions of biological ions with surfaces and of collision-induced dissociation (CID) of ions. The simulations provide an atomic-level understanding of the collisions and, overall, are in quite good agreement with experiment. An integral component of ion/surface collisions is energy transfer to the internal degrees of freedom of both the ion and the surface. The simulations reveal how this energy transfer depends on the collision energy, incident angle, biological ion, and surface. With energy transfer to the ion's vibration fragmentation may occur, i.e. surface-induced dissociation (SID), and the simulations discovered a new fragmentation mechanism, called shattering, for which the ion fragments as it collides with the surface. The simulations also provide insight into the atomistic dynamics of soft-landing and reactive-landing of ions on surfaces. The CID simulations compared activation by multiple "soft" collisions, resulting in random excitation, versus high energy single collisions and nonrandom excitation. These two activation methods may result in different fragment ions. Simulations provide fragmentation products in agreement with experiments and, hence, can provide additional information regarding the reaction mechanisms taking place in experiment. Such studies paved the way on using simulations as an independent and predictive tool in increasing fundamental understanding of CID and related processes.

Mass spectrometry and computational study of collision-induced dissociation of 9-methylguanine–1-methylcytosine base-pair radical cation: intra-base-pair proton transfer and hydrogen transfer, non-statistical dissociation, and reaction with a water ligand

A combined experimental and theoretical study is presented on the collision-induced dissociation of 9-methylguanine–1-methylcytosine base-pair radical cation ([9MG·1MC]˙⁺) and its monohydrate ([9MG·1MC]˙⁺·H₂O) with Xe and Ar gases.