Atmospherically relevant ion chemistry of ozone and its cation

Rate coefficients for electron-impact dissociation of O3+ to singly charged fragments

Rate coefficients for electron-impact dissociation of O3+ to the O+ and O2+ fragments are calculated for the new, recommended cross section data set and for various collisional conditions. Two sets of the cross section data, measured recently by different experimental groups, are used. These cross sections differ significantly with each other, but are renormalized and optimized to the coherent data base. Rate coefficients for the ozone cation fragmentation are determined using the Maxwellian and the non-thermal electron energy distribution functions (EEDF). In the case of Maxwellian distribution, mean electron energies cover the range from zero up to 2 keV. Non-thermal electron energy distribution functions are adopted from the recent electron observations by the 3-D plasma and energetic particles experiment on the WIND spacecraft. The non-thermal rates are evaluated for the mean electron energies from 4 to 80 eV. The role of the possible contribution of electron-impact dissociation of O3+ to the ozone layer depletion has been emphasized.

Formation of Pyrylium from Aromatic Systems with a Helium:Oxygen Flowing Atmospheric Pressure Afterglow (FAPA) Plasma Source

The effects of oxygen addition on a helium-based flowing atmospheric pressure afterglow (FAPA) ionization source are explored. Small amounts of oxygen doped into the helium discharge gas resulted in an increase in abundance of protonated water clusters by at least three times. A corresponding increase in protonated analyte signal was also observed for small polar analytes, such as methanol and acetone. Meanwhile, most other reagent ions (e.g., O₂^+·, NO⁺, etc.) significantly decrease in abundance with even 0.1% v/v oxygen in the discharge gas. Interestingly, when analytes that contained aromatic constituents were subjected to a He:O₂-FAPA, a unique (M + 3)⁺ ion resulted, while molecular or protonated molecular ions were rarely detected. Exact-mass measurements revealed that these (M + 3)⁺ ions correspond to (M - CH + O)⁺, with the most likely structure being pyrylium. Presence of pyrylium-based ions was further confirmed by tandem mass spectrometry of the (M + 3)⁺ ion compared with that of a commercially available salt. Lastly, rapid and efficient production of pyrylium in the gas phase was used to convert benzene into pyridine. Though this pyrylium-formation reaction has not been shown before, the reaction is rapid and efficient. Potential reactant species, which could lead to pyrylium formation, were determined from reagent-ion mass spectra. Thermodynamic evaluation of reaction pathways was aided by calculation of the formation enthalpy for pyrylium, which was found to be 689.8 kJ/mol. Based on these results, we propose that this reaction is initiated by ionized ozone (O₃^+·), proceeds similarly to ozonolysis, and results in the neutral loss of the stable CHO₂^· radical. Graphical Abstract ᅟ.

Isotope exchange in disulfur monoxide-water charged complexes: a mass spectrometric and computational study

A hitherto unknown, isotope-exchange reaction is studied in ionized gaseous mixtures containing disulfur monoxide and water. The kinetics, mechanism, and intermediate of the reaction are investigated by experimental and theoretical methods. The reactivity of the S(2)O(*+) cation with water is investigated under a wide range of pressures ranging from 10(-7) to 10(-4) Torr, by FT-ICR, TQ, and high-resolution CAD mass spectrometry. In the high-pressure limit the reaction proves to be a route to strongly bound sulfur-containing species.

Three-body breakup in the dissociative recombination of the covalent triatomic molecular ion O3+

We report the first observation of almost exclusive three-body breakup in the dissociative recombination of a covalent triatomic molecular ion O3+. The three-body channel, constituting about 94% of the total reactivity, has been investigated in detail. The atomic fragments are formed in only the first two electronic states, 3P and 1D, while formation in the 1S state has not been observed. The breakup predominantly proceeds through dissociative states with linear geometry.

The N3+ Reactivity in Ionized Gases Containing Sulfur, Nitrogen, and Carbon Oxides

The N(3)(+) reactivity with SO(2), N(2)O, CO(2), and CO is studied by mass spectrometric techniques under a wide range of pressures from 10(-7) to 10(-4) Torr. The kinetics, reaction mechanism, and role of vibrationally excited ions are investigated by experimental and theoretical methods. Key distinguishing features of the N(3) (+) reactivity are evidenced by comparison to N(+) and N(2)(+) ions, which mainly undergo charge-exchange reactions. The N(+) transfer to SO(2) prompts formation of NO(+) ions and neutral oxides NO and SO. The N(+) transfer to N(2)O also leads to NO(+) ions by a process not allowed by spin conservation rules. In both cases no reaction intermediate is detected, whereas CO(2) and CO are captured to form the very stable NCO(2) (+) and NCO(+) ions. NCO(2)(+) ions are characterized for the first time as strongly bound triplet ions of NOCO and ONCO connectivity. DFT and CCSD(T) computations have been carried out to investigate the structural and energetic features of the NCO(2) (+) species and their formation process.

High-resolution pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopic study of the two lowest electronic states of the ozone cation O3+

The pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of jet-cooled O3 has been recorded in the range 101,000-104,000 cm(-1). The origins of the X 1A1-->X+ 2A1 and X 1A1-->A+ 2B2 transitions could be determined from the rotational structure of the bands, the photoionization selection rules, the photoionization efficiency curve, and comparison with ab initio calculations. The first adiabatic ionization energy of O3 was measured to be 101,020.5(5) cm(-1) [12.524 95(6) eV] and the energy difference between the X+ 2A1 (0,0,0) and A+ 2B2 (0,0,0) states was determined to be DeltaT0=1089.7(4) cm(-1). Whereas the X-->X+ band consists of an intense and regular progression in the bending (nu2) mode observed up to v2+=4, only the origin of the X-->A+ band was observed. The analysis of the rotational structure in each band led to the derivation of the r0 structure of O3+ in the X+ [C2v,r0=1.25(2) A,alpha0=131.5(9) degrees ] and A+[C2v,r0=1.37(5) A,alpha0=111.3(38) degrees ] states. The appearance of the spectrum, which is regular up to 102,300 cm(-1), changes abruptly at approximately 102,500 cm(-1), a position above which the spectral density increases markedly and the rotational structure of the bands collapses. On the basis of ab initio calculations, this behavior is attributed to the onset of large-amplitude motions spreading through several local minima all the way to large internuclear distances. The ab initio calculations are consistent with earlier results in predicting a seam of conical intersections between the X+ and A+ states approximately 2600 cm(-1) above the cationic ground state and demonstrate the existence of potential minima at large internuclear distances that are connected to the main minima of the X+ and A+ states through low-lying barriers.

Isotope Exchange in Ionised CO2/COMixtures: The Role of Asymmetrical C2O3+ Ions

A hitherto unknown, atmospherically relevant, isotope-exchange reaction was studied in ionised gaseous mixtures containing carbon dioxide and monoxide. The mechanism of the O exchange, proceeding over a double-minimum potential-energy surface, was positively established by mass spectrometric and theoretical methods that also allowed the identification and characterisation of the C2O3+ intermediate. The increase of internal energy displaces the observed reactivity towards an endothermic reaction path that involves only CO2 and represents an indirect route to the dissociation of carbon dioxide.