Ion–molecule reactions of CoAr₆⁺ with nitrogen oxides N₂O, NO, and NO₂: measuring absolute pressure by shock-freezing of the collision complex

A new method to determine the absolute pressure in an ultra-high vacuum apparatus is tested using ion molecule reactions with CoAr₆⁺. In a collision with a neutral reactant, the complex between Co⁺ and the collision partner is stabilized by evaporation of argon atoms. If CoAr₆⁺ reacts with collision rate, the absolute pressure can be determined by comparing the experimental collision rate with the collision rate calculated from average dipole orientation theory. The experimental results with N₂O, NO, and NO₂ indeed show that the collision complex is frozen out. Comparison of the rates of primary, secondary and tertiary reaction products, however, suggests that not all collisions of CoAr₆⁺ are reactive

Photodissociation and photochemistry of V⁺ (H₂O)n, n = 1–4, in the 360–680 nm region

The photodissociation and photochemistry of V⁺ (H₂O)n, n = 1–4, was studied in the 360–680 nm region in a Fourier transform ion cyclotron resonance mass spectrometer. The light of a high pressure mercury arc lamp was filtered with band pass filters, with center wavelengths from 360 to 680 nm in steps of 20 nm. The bandwidth of the filters, defined as full width at half maximum, was 10 nm. Photodissociation channels are loss of water molecules, as well as loss of atomic or molecular hydrogen, which may be accompanied by loss of water molecules. The most intense absorptions are red shifted with increasing hydration. Theoretical spectra are calculated with time dependent density functional theory. Calculations reproduce all features of the experimental spectra, including the red shift with increasing hydration shell and the overall pattern of strong and weak absorptions

Reactions of hydrated electrons (H2O)n- with formic acid

International audienceThe chemistry of gas phase hydrated electrons (H2O) n- with formic acid is studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Black body infrared radiative dissociation and ligand exchange of water by formic acid molecules take place, accompanied by a small contribution of an intracluster redox reaction. During incorporation of the first formic acid molecule, the electron may recombine with the acidic proton and evaporate as a hydrogen atom, leaving formate as new cluster core. At long time scales, all water molecules are exchanged against formic acid, and three formic acid molecules are sufficient to stabilize the electron. For m = 3 and 4, slow formation of (HCOOH)m-1(HCOO -) is observed. This loss of hydrogen may be activated by collisions with HCOOH, resulting in [HCOOH + H] reaction products of unknown structure. © 2006 Elsevier B.V. All rights reserved

Reactions of large water cluster anions with hydrogen chloride: Formation of atomic hydrogen and phase separation in the gas phase

International audienceThe reactions of water cluster anions (H2O)n-, n = 30-70, with hydrogen chloride have been studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The first HCl taken up by the clusters is presumably ionically dissolved. The solvated electron recombines with the proton, which is thereby reduced to atomic hydrogen and evaporates from the cluster. This process is accompanied by blackbody radiation and collision induced loss of water molecules. Subsequent collisions lead to uptake of HCl and loss of H2O, yielding mixed clusters Cl-(HCl)m(H2O)n until they are saturated with HCl. Those saturated clusters lose H2O and HCl in a characteristic sequence. The final stage of the reaction, involving clusters with m = 0-4 and n = 0-6, is studied in detail with density functional theory calculations. The Cl-(HCl)4(H2O)6 cluster represents an example for supramolecular self-organization in the gas phase: it consists of a tetrahedral Cl-(HCl)4, connected on one side of the tetrahedron to a compact water hexamer. © 2007 American Chemical Society