Mass spectrometric contributions to problems related to the chemistry of atmospheres

Photoinduced Sulfur-Nitrogen Bond Rotation and Thermal Nitrogen Inversion in Heterocumulene OSNSO

An exotic ternary S, N, O heterocumulene OSNSO in syn-syn (A) and syn-anti (B) conformations has been generated in the gas phase through flash vacuum pyrolysis of CF₃S(O)NSO at 700 K. Upon visible light irradiation (570 ± 20 or 532 nm), both A and B, isolated in cryogenic matrices (N₂, Ne, Ar, and Kr, <30 K), convert to a higher-energy anti-anti conformer (C). The reverse conformational transformation occurs either through S═N bond rotation (C to A and B) under visible light irradiation (400 ± 20 nm) at 2.8 K or through thermal nitrogen inversion (C to A) in the temperature range of 20-30 K, for which an exceptionally low activation barrier of 1.18 ± 0.07 kcal mol^-1 has been experimentally determined.

SSOH and HSSO Radicals: An Experimental and Theoretical Study of [S2OH]0/+/- Species

New radicals containing sulfur-sulfur bonds are detected in the gas phase: disulfur hydroxide SSOH and thiosulfenoxide HSSO, stable toward dissociation by ca. 50 and 40 kcal mol(-1), respectively. Energetic, structural features and fragmentation pathways of these [S2OH] radicals and their charged species [S2OH]+ and [S2OH]- are experimentally and computationally investigated by mass spectrometric techniques and ab initio calculations. [S2OH]+ is obtained by various ion-molecule reactions leading to S2O protonated on the oxygen and end-sulfur atoms, whose proton affinity is computed at different levels of theory. The first detection of [S2OH]-, the conjugate base of the oxatrisulfane HSSOH, is also reported.

Ions in space

We review the detection history, observation, distribution, and reactivity of molecular ions in extraterrestrial space, with particular (though not exclusive) reference to interstellar monocations. The diversity of interstellar ion chemistry is highlighted with reaction examples, drawn from the authors' own laboratories and elsewhere, and attempt to provide an overview of this broad and increasingly divergent field. Emphasis is given to the role of ions in the synthesis of molecules, including their ability to catalyze the transformation of neutral molecules.

Direct Experimental Observation of CS2OH

The first experimental detection of CS(2)OH is reported. CS(2)OH was observed for about one microsecond after its formation, as an intact isolated species in the gas phase. It was generated by electron transfer to the CS(2)OH(+) ion, prepared in the source of a multisector mass spectrometer by suitable ion-molecule reactions. The vertical formation process allowed characterization of CS(2)OH by structural analysis of CS(2)OH(+). Theoretical calculations were performed at the B3LYP/6-311+G(2d,p) and CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2d,p) levels of theory. The computed structure and stability of CS(2)OH and CS(2)OH(+) as well as the energetics of the involved processes satisfactorily fit with the experimental results.

S3O and S3O+ in the gas phase: ring and open-chain structures

Ring and open-chain S3O sulfur oxides are detected by neutralization-reionization experiments.

Atmospherically relevant ion chemistry of ozone and its cation

The importance of ionic processes that occur in terrestrial, planetary, and stellar atmospheres is receiving increasing recognition. Actually, ions play important, often crucial, roles in a variety of atmospheric processes throughout the universe, and a strong link with the neutral chemistry is also apparent. In the terrestrial atmosphere, the ionic reactions are most relevant in those transient and fleeting events, e.g., lightning, coronas (in thunderstorm clouds and along power lines), where the local ion density is much higher than in unperturbed air, and the chemical systems are typically far from equilibrium. In such cases, ozone, a key molecule for the terrestrial atmosphere, is also present in high local concentrations; it is formed from O(2) by the same transient event. Accordingly, this review provides a survey of the positive ion chemistry of ozone with several of the most important "atmospheric" species: the reactions, the products, and the importance of the examined processes are discussed also in the light of the local thermodynamic disequilibrium (LTD) approach to the chemistry of transient atmospheric events. In all such studies, mass spectrometry is traditionally, and remains today, the experimental technique of choice. The novel application of mass spectrometry to the study of neutral species (NRMS), highly successful for the preparation and positive detection of long-sought, otherwise inaccessible, short-lived neutrals, makes mass spectrometry the most powerful tool now available for the study of the species and processes that are relevant to atmospheric chemistry. Selected examples of the interlink between the neutral and the ionic chemistry are also illustrated.

Charged and neutral NO3 isomers from the ionization of NOx and O3 mixtures

Mass spectrometric techniques have been utilized in conjunction with theoretical methods to detect and characterize new species formed upon ionization of gaseous mixtures containing ozone and an NOx oxide. NO5+ as well as isomeric NO4+ and NO3+ ions have been identified. Moreover, utilization of neutralization reionization mass spectrometry (NRMS) has provided strong evidence for, if not a conclusive demonstration of, the existence of a new NO3 isomer, in addition to the long-known trigonal radical, as a gaseous species with a lifetime in excess of approximately 1 microsecond.