The following full text is a publisher's version.For additional information about this publication click this link. https://hdl.handle.net/2066/227109Please be advised that this information was generated on 2022-07-11 and may be subject to change.

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.

No abstract

The hydrated radical anions CO − 3 (H 2 O) 1,2 and CO − 4 (H 2 O) 1,2 are important anions in the atmosphere. Quantitative models predict the steady state fractional abundance of CO − 3 (H 2 O) 0,1 to be in the range of 0.3-2.3 % of the total negative ion inventory, with CO − 3 (H 2 O) being predicted to be dominating up to an altitude of 11 km [1]. Direct sampling of ions in the boreal forest confirmed the presence of. The CO − 4 ion is another radical anion that is derived from CO 2 and found with a fractional abundance of about 0.01 % [2]. The reactivity often depends strongly on the number of solvating water molecules [3], and therefore the hydration structure is key to understand their reactivity. Infrared multiphoton dissociation (IRMPD) spectroscopy is an excellent tool to collect information on the structure of ions. The spectra were measured in both the C-O and O-H stretch region at ion trap temperatures of 295 K and approx. 80 K [4]. The O-H stretching region exhibits broad spectra with additional maxima and shoulders beside the free O-H stretch frequency for all ions. Clear absorptions are observed in the C-O stretching region, but dissociation of CO − 3 (H 2 O) 1,2 was surprisingly inefficient, probably due to radiative cooling. While CO − 3 (H 2 O) 1,2 and CO − 4 (H 2 O) lose water upon dissociation, CO −4 (H 2 O) 2 exhibits an additional dissociation channel with loss of CO 2 . All experimentally measured infrared spectra are compared to calculated spectra within harmonic approximation and from analysis of molecular dynamics (MD) simulations. The comparison of experiment and theory indicates that multiple isomers contribute to the observed spectrum at finite temperatures.[1] H. Kawamoto and T.

Proton transfer reactions (PTR) are important for chemical ionization, especially in trace gas analysis in air. In an effort to extend their application to the analysis of high‐purity inert gases, we studied PTR of N2H+ and ArH+ with various reaction gases, viz. O2, N2, CH4, CO2, NO2, H2O and CH3OH. Oxygen, nitrogen, methane, carbon dioxide, and water undergo non‐dissociative proton transfer, where the original molecule remains intact. PTR to nitrogen dioxide leads to NO+ with release of neutral OH⋅. While PTR from N2H+ to methanol exclusively yields protonated methanol, the reaction with ArH+ exhibits dissociative proton transfer, due to its higher exothermicity. Products include methenium, protonated formaldehyde, and protonated methanol. The latter undergoes a slow secondary reaction to form protonated dimethyl ether. Within error limits, most reactions proceed at or close to collision rate. Quantum chemical calculations provide energetics and reaction pathways. In such highly exothermic proton transfer reactions, identification and quantification of trace compounds require detailed understanding of the fragmentation pathways and branching ratios.