Search

The reactivity of [NaL·ClO2]− cluster anions (L = ClOx−; x = 0–3) with sulphur dioxide has been investigated in the gas phase by ion–molecule reaction experiments (IMR) performed in an in-house modified Ion Trap mass spectrometer (IT-MS). The kinetic analysis revealed that SO2 is efficiently oxidised by oxygen-atom (OAT), oxygen-ion (OIT) and double oxygen transfer (DOT) reactions. The main difference from the previously investigated free reactive ClO2− is the occurrence of intracluster OIT and DOT processes, which are mediated by the different ligands of the chlorite anion. This gas-phase study highlights the importance of studying the intrinsic properties of simple reacting species, with the aim of elucidating the elementary steps of complex processes occurring in solution, such as the oxidation of sulphur dioxide.

The reactivity of carbonate cluster ions with sulfur dioxide has been investigated in the gas phase by mass spectrometric techniques. SO2 promotes the displacement of carbon dioxide from carbonate clusters through a stepwise mechanism, leading to the quantitative conversion of the carbonate aggregates into the corresponding sulfite cluster ions. The kinetic study of the reactions of positive, negative, singly, and doubly charged ions reveals very fast and efficient processes for all the carbonate ions.

The synthesis of cationic mono oxo MoIV PNP pincer complexes of the type [Mo(PNPMe-iPr)(O)X]+ (X = I, Br) from [Mo(PNPMe-iPr)(CO)X2] is described. These compounds are coordinatively unsaturated and feature a strong Mo≡O triple bond. The formation of these complexes proceeds via cationic 14e intermediates [Mo(PNPMe-iPr)(CO)X]+ and requires both molecular oxygen and water. ESI MS measurements with 18O labeled water (H2 18O) and molecular oxygen (18O2) indicates that water plays a crucial role in the formation of the Mo≡O bond. A plausible mechanism based on DFT calculations is provided. The X-ray structure of [Mo(PNPMe-iPr)(O)I]SbF6 is presented.

Unprecedented hydrolysis reactions are observed in the gas phase in clusters containing doubly-charged vanadium oxides and hydroxide anions, SO2 and H2O. The experimental and computational study shows the cooperative effects of the vanadium species, V2O62− and HV3O92−, and sulfur dioxide on the enhancement of the hydrogen bonds of water that allows the acid–base reaction and charge separation in the doubly-charged ion.

The reactivity of transition metal dioxide anions of cobalt, nickel, copper and zinc with sulfur dioxide has been investigated in the gas phase by mass spectrometric techniques and theoretical calculations. Dioxide anions of the late transition metals Cu and Zn promote an unprecedented fast and efficient oxidation to the sulfate radical anion through a double oxygen transfer, whereas the earlier transition metals Ni and Co only undergo the addition of two SO2 molecules. The ligation of a water molecule to ZnO2 − switches the reaction path to a single oxygen anion transfer, forming SO3 −.

The gas-phase reactivity of doubly-charged vanadium hydroxides anions with SO2 has been studied by experimental and computational methods. The obtained results highlight the role of sulfur dioxide in promoting unprecedented bond-forming reactions, which produce singly-charged products by breaking the Vx Oy skeleton or a terminal V-O bond.

Unprecedented redox reactions of chromium oxide anions have been observed in the gas phase and investigated by mass spectrometric techniques and electronic structure calculations. The effective oxidizing and reducing power of chromium oxide anions is unravelled by sulfur dioxide: CrO4 − and CrO2 − generate CrO3 − as the reduction and oxidation product, respectively, together with SO3 and SO as the oxidation and reduction products of SO2, respectively. Computations predict that the reactions of CrO4 − and CrO2 − proceed through rather stable ion-dipole complexes and that CrO4 - produces also a strongly bound [CrSO6] - species.

H 2 O 2 + ions are shown to be formed in ionized O2/CH4 mixtures from the secondary reaction of CH2O+ with O2. By high-resolution mass spectrometric techniques, the peroxide HOOH structure and the H2CO structure of ionized formaldehyde are assigned to the [H2O2]+ ions and the [CH2O]+ reactants, respectively. The [CH4O2]+ intermediate of the reaction between O 2 + and CH4 is characterized as a mixture of the loosely bound [ CH 4 O 2 ] + complex and the theoretically predicted insertion product CH3OOH+. The CH3OOH+ intermediate, precursor of the most abundant ionic product CH2OOH+, has been characterized for the first time as a long-lived species.

The HOOO− anion, the conjugate base of dihydrogen trioxide, HOOOH, is suggested as a key intermediate in ozonation reactions relevant to atmospheric chemistry, water purification, preparative organic chemistry, etc. Whereas recent theoretical calculations characterize HOOO− as a long-lived metastable species, so far the anion proved experimentally elusive, defying attempts at its direct detection even in solution, where it should be stabilized by solvation. We report the preparation and the proof-positive detection of HOOO− as an isolated species with a lifetime >0.8 μs. The preparation proved particularly difficult, since the only viable approach is the indirect route involving the preliminary formation of HOOO upon neutralization of HOOO+, followed by electron attachment to the radical, utilizing neutralization–reionization ( + NR − ) mass spectrometry. Direct two-electron reduction of the HOOO+ cation to the HOOO− anion by the vertical process typical of charge reversal (CR) experiments proved inefficient. This observation, and application of neutral and ion decomposition difference (NIDD) mass spectrometry, pioneered by Schwarz and coworkers [Int. J. Mass Spectrom. Ion Processes 172 (1998) 181] suggest that the geometries of HOOO+ and HOOO− are significantly different, whereas that of the HOOO radical is structurally intermediate between them, which accounts for the diversity of the Franck–Condon factors characterizing the mutual vertical transitions of the three species. This inference is consistent with the available optimized geometries of HOOO and HOOO+, computed at various levels of theory, and with that of the anion recently reported by Plesnicar et al. [J. Am. Chem. Soc. 124 (2002) 8462].

The oxidation of SO2 by nonmetal oxoanions in the gas phase is investigated in an experimental and theoretical study of the structure of the species involved and the reaction kinetics and mechanism. SO3 , SO3(.-) and SO4(.-) are efficiently produced by reaction of On XO(-) anions (X=Cl, Br, and I; n=0 and 1) with SO2 ; XO(-) ions mainly react to give SO3 by oxygen-atom transfer, whereas OXO(-) ions mainly give SO3(.-) by oxygen-anion transfer. On descending the halogen group from chlorine to iodine, the SO3 /SO3(.-) ratio decreases and increases for reactions involving XO(-) and OXO(-) anions, respectively, whereas the formation of SO4(.-) is particularly significant with OIO(-). Kinetic factors play a major role in the reactions of On XO(-), depending on the halogen atom and its oxidation state.

Recent mass spectrometric studies of simple inorganic species (both charged and neutral) of main-group elements are reviewed, focusing attention on radicals and ions of interest to the chemistry of the atmosphere and its pollution. The examples illustrated concern the detection of HO 3 , hydrogen trioxide, the O 2 /O 3 isotope exchange and its charged intermediate O 5 + , the reactions promoted by ionization of ozone/halocarbon mixtures in atmospheric gases, the ion chemistry of NO x oxides, and that of elemental chlorine and chlorine fluoride. Among the results of specific interest to gas-phase ion chemistry, the examples illustrated concern the intracluster ligand-switching reactions in ternary NO + complexes, the NO 2 + reactivity towards ethylene and acetylene, the gas-phase basicity of Cl 2 , the formation and characterization of Cl 2 X + ions (X = Cl, F) and of [H 3 C-Cl-Cl] + , a new isomer of protonated dichloromethane.

Gaseous [HN2O5]+ ions formed upon addition of NO2+ to nitric acid have been studied by mass spectrometric and computational methods. The results from MIKE, CAD and FT-ICR spectrometry and calculations at the B3LYP 6-311++G(3df, 3dp)//6-311G(d,p) level of theory show that the most stable adduct formed is an electrostatic HNO3·NO2+ complex where NO2+ is coordinated to the nitro group of nitric acid. Consequently, the nitro group is the energetically preferred protonation site of N2O5, whose experimental proton affinity (PA) amounts to 189.8 ± 2 kcal mol-1, vs theoretically computed values ranging from 182 to 188 kcal mol-1. Addition of NO2+ to XNO2 molecules (X = CH3O, C2H5O and NH2) also yields electrostatic complexes where the nitronium ion is coordinated to the NO2 group. The most stable [HN2O4]+ ion from the addition of NO+ to HNO3 is also identified as a cluster characterized by coordination of the nitrosonium ion to the nitro group, whose almost thermoneutral isomerization into a cluster where a nitro...

It has long been assumed that ionizing neutral acetonitrile produces ions with the same atomic connectivity, CH(3)CN(+*). Recent calculations on the C(2)H(3)N(+*) potential energy surface have suggested that it may be difficult to generate pure CH(3)CN(+*) when ionizing acetonitrile. We have probed the interconversion of CH(3)CN(+*) and its lower energy isomer CH(2)CNH(+*) by calculation, collision-induced dissociation mass spectrometry and ion-molecule reaction. The latter ion, ionized ketenimine, is co-generated upon electron or chemical ionization of neutral acetonitrile in the ion source of a mass spectrometer. An estimate of the ratio of the two isomers can be obtained from their respective ion-molecule reactions with CO(2) or COS. CH(3)CN(+*) reacts by proton-transfer with CO(2) and charge transfer with COS, whereas CH(2)CNH(+*) is unreactive.

The Proton Affinity and Gas-Phase Basicity of Sulfur Dioxide

The room-temperature C-H activation of ethane by metal-free SO2 center dot+ radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H2SO2 center dot+ the radical cation of sulfoxylic acid. The mechanism of the double C-H activation, in the absence of the single activation product HSO2+, is elucidated by kinetic studies and quantum chemical calculations. Under near single-collision conditions the reaction occurs with rate constant k = 1.0 x 10(-9) (+/-30%) cm(3) s(-1) molecule(-1), efficiency = 90%, kinetic isotope effect k(H)/k(D)=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO2 center dot+ with ethane through an oxygen atom directly leads to the C-H activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double C-H activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron-transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal-free electrophiles may contribute to the current understanding of the C-H activation of ethane.

The oxywater cation H2OO+ was generated in the gas phase by ionization of mixtures containing O3, O2 and H2O. Different ionic mixtures, rich in either the H2OO+ or the HOOH+ isomer, were obtained by O3/O2/H2O–O2/H2O CI, and by CH3OH/O2–CH2O/O2 CI, respectively. The H2O2+ ions were characterized by high-resolution CAD mass spectrometry, and structural and energetic effects were examined.

The N3+ reactivity with SO2, N2O, CO2 and CO is studied by mass spectrometric techniques under a wide range of pressures ranging from 10-7 to 10-4 Torr. The N+ transfer features the N3+ reactivity with these simple inorganic molecules. The kinetics, reaction mechanism and the role of vibrationally excited ions are investigated by experimental and theoretical methods. Key distinguishing features of the N3+ reactivity are evidenced by comparison to N+ and N2+ ions, that mainly undergo charge exchange reactions. The N+ transfer to SO2 prompts formation of NO+ ions and neutral oxides NO and SO. The N+ transfer to N2O also leads to NO+ by a process not allowed by spin conservation rules. In both cases no reaction intermediate is detected, whereas CO2 and CO are captured to form the very stable NCO2+ and NCO+ ions. NCO2+ 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 NCO2+ species and their formation process.

An ionic route to the CS2 degradation was studied by mass spectrometric and theoretical methods. Ionized mixtures containing carbon disulfide and ozone prove an effective source of S2+andSO+ ions, formed by remarkable molecular reorganization and open to further reactions with ozone and surrounding species. Both the O-transfer and dissociative oxidation processes, typical of the O3 reactivity in ionized mixtures, were observed.

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.

Gaseous ionized carbonyl sulfide/ozone mixtures have been studied by mass spectrometric techniques and theoretical calculations. The evidence obtained points to this system as an effective route to the SO+ ion, which in turn promotes a rich ion chemistry leading to SnO+ (n = 2−5) and Sn+ (n = 2−9) ions via oligomerization processes.

No Abstract

The chemistry of the title cations was investigated in the gas phase by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and by theoretical methods. Cl2H+ (1) was obtained from the protonation of Cl2 by gaseous Bronsted acids and the chlorination of HCl by Cl2F+ and XeCl+. The proton affinity (PA) of Cl2 measured by the FT-ICR equilibrium method is 131.4 ± 1 kcal mol-1 at 298 K, which compares with the 132.0 kcal mol-1 value computed at the CCSD(T) level of theory. 1 has the Cl−Cl−H connectivity, as indicated by its 2-fold reactivity as a Bronsted acid and a chlorinating agent, and confirmed by the theoretical results. The FClH+ cation was obtained from the fluorination of HCl by XeF+ and its most stable protomer (2) has the F−Cl−H connectivity, as shown by its behavior as a pure Bronsted acid and by the theoretical results that identify 2 as the global minimum, whereas protomer 3, having the H−F−Cl connectivity, is computed to be less stable by 5.0 kcal mol-1 at the CCSD(T) level of t...

H 4 PO + 3 ions have been generated in a mass spectrometer by proton-transfer to H 3 PO 3 from different Bronsted acids. The proton affinity of H 3 PO 3 has been estimated by bracketing and kinetic methods to be 198.6 ± 2 kcal mol −1 . Gaseous H 4 PO + 3 ions have been structurally assessed by metastable ion kinetic energy (MIKE) and collisionally induced dissociation (CID) mass spectrometry leading to the detection of a single isomeric species. The chemistry of H 2 PO − 3 is characterized by facile addition-elimination reactions leading to formation of polyanions. Species containing up to six P atoms have been detected.

S3O, a novel, linear sulfur oxide has been detected in the gas phase by means of neutralization reionization mass spectrometry; the upper limit of stability of acyclic forms of SnO oxides has been set by theoretical calculations.

The cover pictures shows…‥the mass spectrum of nitrogen hydroxide oxide, the H2NO3. radical, which was discovered by neutralization reionization mass spectrometry (NRMS) and characterized as a relatively long-lived (over 1 μs) metastable species. The discovery required the availability of the appropriate charged precursor that fortunately had previously been prepared by this group (1989) as a result of their sustained interest in gas-phase ion chemistry of nitrates, nitrites and related molecules. Cacace et al. found that protonation of nitric acid by strong Bronsted acids yields, in addition to the H2ONO2+ ion, smaller amounts of the less stable (HO)2NO+ isomer, namely charged nitrogen hydroxide oxide. This result has allowed the present discovery by NRMS (yellow trace), whereas NRMS of the H2ONO2+ ion does not result in detectable H2NO3. neutral species (green trace). The importance of nitrogen hydroxide oxide stems from its relevance to a variety of research areas, from the reduction of the NO32− anion, to atmospheric chemistry, radiolysis of nuclear-waste solutions, the charge-transfer mechanism of aromatic nitration, etc. Find out more in the communication by Cacace et al. on pp. 1128–131.

The reactions occurring upon ionization of mixtures containing ozone and CHX2Y (X = H, Cl, F; Y = Cl, F) halocarbons diluted in atmospheric gases (O2, N2) have been investigated in detail by mass spectrometric and theoretical methods. In all systems investigated the reactivity pattern is characterized by the preliminary formation of [CHXY x O3+] adducts which undergo unimolecular dissociation into HXYO2+ and CO. This remarkable dissociation which requires extensive molecular reorganization is exceptional for hydrogenated halocarbons. The work represents the first systematic study of the ionic chemistry in systems containing both ozone and halocarbons diluted in atmospheric gases.