Intramolecular energy transfer rates in photoexcited cluster ions: The photodissociation dynamics of CO−3⋅H2O and CO−3⋅CO2

Infrared spectroscopy of CO3 •-(H2O)1,2 and CO4 •-(H2O)1,2

Hydrated molecular anions are present in the atmosphere. Revealing the structure of the microsolvation is key to understanding their chemical properties. The infrared spectra of CO₃ ^•-(H₂O)_1,2 and CO₄ ^•-(H₂O)_1,2 were measured via infrared multiple photon dissociation spectroscopy in both warm and cold environments. Redshifted from the free O-H stretch frequency, broad, structured spectra were observed in the O-H stretching region for all cluster ions, which provide information on the interaction of the hydrogen atoms with the central ion. In the C-O stretching region, the spectra exhibit clear maxima, but dissociation of CO₃ ^•-(H₂O)_1,2 was surprisingly inefficient. While CO₃ ^•-(H₂O)_1,2 and CO₄ ^•-(H₂O) dissociate via loss of water, CO₂ loss is the dominant dissociation channel for CO₄ ^•-(H₂O)₂. The experimental spectra are compared to calculated spectra within the harmonic approximation and from analysis of molecular dynamics simulations. The simulations support the hypothesis that many isomers contribute to the observed spectrum at finite temperatures. The highly fluxional nature of the clusters is the main reason for the spectral broadening, while water-water hydrogen bonding seems to play a minor role in the doubly hydrated species.

Hydration Leads to Efficient Reactions of the Carbonate Radical Anion with Hydrogen Chloride in the Gas Phase

The carbonate radical anion CO₃^•- is a key intermediate in tropospheric anion chemistry. Despite its radical character, only a small number of reactions have been reported in the literature. Here we investigate the gas-phase reactions of CO₃^•- and CO₃^•-(H₂O) with HCl under ultrahigh vacuum conditions. Bare CO₃^•- forms OHCl^•- with a rate constant of 4.2 × 10^-12 cm³ s^-1, which corresponds to an efficiency of only 0.4%. Hydration accelerates the reaction, and ligand exchange of H₂O against HCl proceeds with a rate of 2.7 × 10^-10 cm³ s^-1. Quantum chemical calculations reveal that OHCl^•- is best described as an OH^• hydrogen bonded to Cl^-, while the ligand exchange product is Cl^-(HCO₃^•). Under tropospheric conditions, where CO₃^•-(H₂O) is the dominant species, Cl^-(HCO₃^•) is efficiently formed. These reactions must be included in models of tropospheric anion chemistry.

Kinetic energy release distributions in mass spectrometry

Kinetic energy releases (KERs) in unimolecular fragmentations of singly and multiply charged ions provide information concerning ion structures, reaction energetics and dynamics. This topic is reviewed covering both early and more recent developments. The subtopics discussed are as follows: (1) introduction and historical background; (2) ion dissociation and kinetic energy release: kinematics; potential energy surfaces; (3) the kinetic energy release distribution (KERD); (4) metastable peak observations: measurements on magnetic sector and time-of-flight instruments; energy selected results by photoelectron photoion coincidence (PEPICO); (5) extracting KERDs from metastable peak shapes; (6) ion structure determination and reaction mechanisms: singly and multiply charged ions; biomolecules and fullerenes; (7) theoretical approaches: phase space theory (PST), orbiting transition state (OTS)/PST, finite heat bath theory (FHBT) and the maximum entropy method; (8) exit channel interactions; (9) general trends: time and energy dependences; (10) thermochemistry: organometallic reactions, proton-bound clusters, fullerenes; and (11) the efficiency of phase space sampling.