Electron Impact Ionization Mass Spectrometry Research Articles

Self-reducing precursors for aluminium metal thin films: evaluation of stable aluminium hydrides for vapor phase aluminium deposition.

Thin films of Al as interconnect materials and those of AlN as wide bandgap semiconductor and piezoelectric material are of great interest for microelectronic applications. For the fabrication of these thin films via chemical vapor deposition (CVD) based routes, the available precursor library is rather limited, mostly comprising aluminium alkyls, chlorides, and few small amine-stabilized aluminium hydrides. Herein, we focused on rational precursor development for Al, their characterization and comparison to existing precursors comprising stabilized aluminium hydrides. We present and compare a series of potentially new and reported aluminium hydride precursors divided into three main groups with respect to their stabilization motive, and their systematic structural variation to evaluate the physicochemical properties. All compounds were comprehensively characterized by means of nuclear magnetic resonance spectroscopy (NMR), Fourier-transform infrared spectroscopy (FTIR), elemental analysis (EA), electron-impact ionization mass spectrometry (EI-MS) and thermogravimetric analysis (TGA). Promising representatives were further evaluated as potential single source precursors for aluminium metal formation in proof-of-concept experiments. Structure and reaction enthalpies with NH3 or H2 as co-reactants were calculated via first principles density functional theory simulations and show the great potential as atomic layer deposition (ALD) precursors for Al and AlN thin films.

Analysis of organochlorine pesticides in contaminated soil by GC-MS/MS using accelerated solvent extraction as a green sample preparation

ABSTRACT Organochlorine pesticides (OCPs), persistent organic pollutants, in the contaminated soil have been analysed by a gas chromatography-tandem mass spectrometry (MS) in this work. OCPs were extracted with a mixture of dichloromethane and n-hexane by using accelerated solvent extraction at elevated temperature and high pressure. The extractant was concentrated by a rotary vacuum evaporator and cleaned up by silica gel solid phase extraction. OCPs were then separated by a gas chromatography in combination with an electron impact ionisation MS in MS/MS mode. The limit of detection, limit of quantification and other important parameters of the GC-EI-MS/MS analytical method, such as repeatability, recovery and so on, have been investigated and presented. Limit of detection and limit of quantification have been achieved from 0.005 ng g−1 (p,p’-DDE) to 0.405 ng g−1 (dieldrin) and 0.016 ng g−1 to 1.216 ng g−1, respectively. The repeatability of this method was achieved below 8.3% and 13.7% for short- and long-term stability. Recovery of all OCPs ranged from 78.1% ± 1.5% to 117.5% ± 3.2%. The developed analytical method was validated by spiking experiments in the real samples. The validated method has been then used for the analysis of OCPs in the soil samples that were collected from the contaminated areas in Vietnam. Results showed the presence of hexachlorocyclohexane isomers and p-p’-DDT in all analysed samples at elevated levels.

Crannenols A-D, Sesquiterpenoids from the Irish Deep-Sea Soft Coral Acanella arbuscula.

Four undescribed sesquiterpenoids, crannenols A-D (1-4), have been isolated from CHCl2 and MeOH extracts of the deep-sea bamboo coral Acanella arbuscula. The corals were collected from a submarine canyon on the edge of Ireland's Porcupine Bank via a remotely operated vehicle. The structure elucidation of these (Z,E)-α-farnesene derivatives was achieved using a combination of 1D and 2D NMR, electron impact (1, 2), and electrospray ionization (3, 4) mass spectrometry.

Blue-green light is required for a maximized fatty acid unsaturation and pigment concentration in the microalga Acutodesmus obliquus.

Blue-green light is known to maximize the degree of fatty acid (FA) unsaturation in microalgae. However, knowledge on the particular waveband responsible for this stimulation of FA desaturation and its impact on the pigment composition in microalgae remains limited. In this study, Acutodesmus obliquus was cultivated for 96 h at 15°C with different light spectra (380-700 nm, 470-700 nm, 520-700 nm, 600-700 nm, and dark controls). Growth was monitored daily, and qualitative characterization of the microalgal FA composition was achieved via gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Additionally, a quantitative analysis of microalgal pigments was performed using high-performance liquid chromatography with diode array detection (HPLC-DAD). Spectra that included wavelengths between 470 and 520 nm led to a significantly higher percentage of the polyunsaturated fatty acids (PUFA) 18:3 and 16:4, compared to all other light conditions. However, no significant differences between the red light cultivations and the heterotrophic dark controls were observed for the FA 18:3 and 16:4. These results indicate, that exclusively the blue-green light waveband between 470 and 520 nm is responsible for a maximized FA unsaturation in A. obliquus. Furthermore, the growth and production of pigments were impaired if blue-green light (380-520 nm) was absent in the light spectrum. This knowledge can contribute to achieving a suitable microalgal pigment and FA composition for industrial purposes and must be considered in spectrally selective microalgae cultivation systems.

Growth and fatty acid composition of Acutodesmus obliquus under different light spectra and temperatures.

The combined impact of temperature and light spectra on the fatty acid (FA) composition in microalgae has been sparsely investigated. The aim of this study was to investigate the interactions of light and temperature on the FA composition in Acutodesmus obliquus. For this purpose, A. obliquus was cultivated with different temperatures (20, 30, and 35°C), as well as broad light spectra (blue, green, and red light). Growth and FA composition were monitored daily. Microalgal FA were extracted, and a qualitative characterization was done by gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Compared to red light, green and blue light caused a higher percentage of the polyunsaturated fatty acids (PUFA) 16:4, 18:3, and 18:4, at all temperatures. The highest total percentage of these PUFA were observed at the lowest cultivation temperature and blue and green light. These data imply that a combination of lower temperatures and blue-green light (450-550 nm) positively influences the activity of specific FA-desaturases in A. obliquus. Additionally, a lower 16:1 trans/cis ratio was observed upon green and blue light treatment and lower cultivation temperatures. Remarkably, green light treatment resulted in a comparably high growth under all tested conditions. Therefore, a higher content of green light, compared to blue light might additionally lead to a higher biomass concentration. Microalgae cultivation with low temperatures and green light might therefore result in a suitable FA composition for the food industry and a comparably high biomass production.

Modification of the Lipid Profile of the Initial Oral Biofilm In Situ Using Linseed Oil as Mouthwash.

Lipids are of interest for the targeted modification of oral bioadhesion processes. Therefore, the sustainable effects of linseed oil on the composition and ultrastructure of the in situ pellicle were investigated. Unlike saliva, linseed oil contains linolenic acid (18:3), which served as a marker for lipid accumulation. Individual splints with bovine enamel slabs were worn by five subjects. After 1 min of pellicle formation, rinses were performed with linseed oil for 10 min, and the slabs’ oral exposure was continued for up to 2 or 8 h. Gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS) was used to characterize the fatty acid composition of the pellicle samples. Transmission electron microscopy was performed to analyze the ultrastructure. Extensive accumulation of linolenic acid was recorded in the samples of all subjects 2 h after the rinse and considerable amounts persisted after 8 h. The ultrastructure of the 2 h pellicle was less electron-dense and contained lipid vesicles when compared with controls. After 8 h, no apparent ultrastructural effects were visible. Linolenic acid is an excellent marker for the investigation of fatty acid accumulation in the pellicle. New preventive strategies could benefit from the accumulation of lipid components in the pellicle.

Time-Resolved Quantification of Phenolic Antioxidants and Oxidation Products in a Model Fuel by GC-EI-MS/MS

Phenol-type components, such as butylated hydroxytoluene (BHT), are used as antioxidants (AOs) to enhance the thermo-oxidative stability of kerosene-type Jet A-1 fuel. Although the antioxidative effect of BHT is well known and often published, there is far less information about the degradation products of BHT in fuels and their impact on stability toward oxidation. In order to monitor a time-resolved depletion of BHT in model kerosene, an artificial alteration method adapted for regular sampling was applied. Subsequently, the molecular structure of degradation products of BHT was identified by gas chromatography with electron impact ionization mass spectrometry (GC-EI-MS). For the quantification of the residual BHT as well as the two representatives of degradation products, namely, 3,5-di-tert-butyl-4-hydroxybenzaldehyde (HBA) and 2,6-di-tert-butyl-p-benzoquinone (BQ), an analytical technique comprising a GC-EI triple quadrupole mass spectrometer run in the MS/MS mode was developed. The limit of detection (LOD) and the limit of quantification (LOQ) for BHT, BQ, and HBA were determined below 1 ppb. The formation of BQ and HBA was observed shortly after the nascent degradation of BHT, while an increase of oxidation products derived from the fuel ascended remarkably after a full depletion of both the initial AO BHT and the monitored oxidation products BQ and HBA. As the evolution of BQ and HBA followed a characteristic trend, these compounds can be used as markers to reliably predict the residual time until a total consumption or a predefined threshold of BHT is reached. This way, the quality management of in-service or stored kerosene-type fuels is enhanced.

Effect of hydration and structure on the fragmentation of 2,2-(propane-1,3-diyl)bis(isoindoline-1,3-dione) and 2,2-(ethane-1,2-diyl)bis(isoindoline-1,3-dione) in electron impact ionization-mass spectrometry: A theoretical and experimental study

Two bis-phthalimide derivatives, 2,2-(ethane-1,2-diyl)bis(isoindoline-1,3-dione) (3) and 2,2-(propane-1,3-diyl)bis(isoindoline-1,3-dione) (4) were synthesized and characterized by 1H NMR, 13C NMR and electron impact ionization-mass spectrometry (EI-MS). Effect of the alkyl length on the fragmentation of the compounds 3 and 4 was investigated and it was found that molecular ion of 3 with a CH2–CH2 group is almost completely decomposed, so that a small peak was observed for its molecular ion at m/z of 320. On the other hand, an intense peak with m/z of 334 was observed for the molecular ion of 4 indicating the stability of 4+ ion. The results were interpreted using computational method at B3LYP/6-31 + G(d) level of theory. Also, comparison of the mass spectra showed that the cation 4+ is tri-hydrated while 3+ is not hydrated. From the optimized structures of 4+(H2O)1-3 clusters, it was found that the extra stability of 4+(H2O)3 is due to formation of hydronium ion (H2O)2H3O+.

Ammonium Salts as a Source of Small Molecules Observed with High-Resolution Electron-Impact Ionization Mass Spectrometry.

Recent high-resolution in situ mass spectrometry at comet 67P/Churyumov-Gerasimenko visited by European Space Agency's Rosetta spacecraft raised the question, if sublimating ammonium salts can unequivocally be detected in the cometary coma. In laboratory experiments with the twin model of the space instrument, two prototypic ammonium salts NH4B, namely, ammonium chloride (B = Cl-) and ammonium formate (B = HCOO-) (as well as methodologically relevant isotopologues), were allowed to sublimate in vacuum while mass spectra were collected. High-resolution electron-impact ionization mass spectrometry provides an outstanding experimental tool to investigate the complex physicochemical processes occurring during the sublimation of ammonium salts. Sublimation of ammonium chloride led to the observation of the ammonium cation NH4+ and the chloramide molecule NH2Cl in the neutral gas mode of the instrument. These observations could be jointly interpreted as indirect evidence for the existence of a neutral gaseous parent species (either as the molecular complex NH3···HB or the double-ionic species NH4+···B-). However, the qualitative fragmentation pattern we present for 13C15N-ammonium formate suggests an alternative route of NH4+ production within the ionization region of the instrument, namely, by protonation/hydrogenation. Besides NH4+, other species were observed that were formed in protonation/hydrogenation reactions. Moreover, together with the two major species from the decomposition of the salt, ammonia and formic acid, three minor species also contributed to the fragmentation pattern: HCN/HNC, HOCN/HNCO, and CH3NO. Like chloramide, formamide (CH3NO) also is a secondary species probably formed in a pseudo-intramolecular chemical reaction while ammonia and the respective acid are in a state of association. HCN/HNC and HOCN/HNCO are ternary products coming out of formamide decomposition reactions. We discuss our experimental findings, summarized in a tentative chemical reaction network, in light of the available theoretical literature and highlight their relevance for the interpretation of in situ measurements in space research.

Soil concentrations of polybrominated diphenyl ethers and trace metals from an electronic waste dump site in the Greater Accra Region, Ghana: Implications for human exposure

Unregulated electronic waste (e-waste) recycling operations have become a significant environmental issue as well as human health risk in developing countries across the world. The present study evaluated the extent of pollution in Agbogbloshie e-waste recycling site in Accra, Ghana. The concentrations of polybrominated diphenyl ethers (PBDEs) and some selected trace metals were determined using gas chromatography electron impact ionization mass spectrometry and flame atomic absorption spectrophotometry, respectively. The concentrations of ∑ PBDEs ranged from 15.6 to 96.8ngg−1 dry weight, with an overall mean of 54.8ngg−1dw. BDE-28 was the dominant congener followed by BDE-209 and BDE-47. The order of mean concentrations of the abundant trace metals was Fe>Cu>Pb≫Mn, with a mean range of .531–289mgkg−1. Geoaccumulation index suggested that the surface soils deteriorated from moderate to high metal pollution, particularly for Cu, Pb and Fe. Of the trace metals analysed, Fe exhibited the highest concentration ranging from 3.97 to 918mgkg−1. Correlation and principal component analyses suggested possible interactions between PBDEs and the trace metals analysed, while source assessment suggested that PBDEs and trace metals were mostly derived from inputs from the e-waste recycling activities. Average daily dose (ADD) was estimated using concentrations corresponding to 5th percentile, median and 95th percentile. Hazard quotients of 380 and 862 were obtained for adults and children respectively, for Cu and Pb which is a cause for concern especially for local children.

EI-MS and ESI–MS/MS study of O,O-dialkyl(diaryl) methylphosphonoselenoates

For the first time, a new series of compounds, O,O-dialkyl(diaryl) methylphosphonoselenoates, listed in Schedule 2.B.04 of the Chemical Weapons Convention was synthesized and investigated by the electron-impact (EI) and electrospray ionization (ESI) mass spectrometry. General EI and ESI fragmentation pathways were proposed and confirmed by analyzing fragment ions of deuterated analogs and by the use of density functional theory (DFT) calculations. Several novel fragmentations and rearrangements, involving an intramolecular selenono-selenolo rearrangement have been observed. The study also suggests that a previously unknown nucleophilic aromatic substitution reaction takes place during the fragmentation process.

Identification and hazard prediction of tattoo pigments by means of pyrolysis-gas chromatography/mass spectrometry.

The implementation of regulation for tattoo ink ingredients across Europe has generated the need for analytical methods suitable to identify prohibited compounds. Common challenges of this subject are the poor solubility and the lack of volatility for most pigments and polymers applied in tattoo inks. Here, we present pyrolysis coupled to online gas chromatography and electron impact ionization mass spectrometry (py-GC/MS) as quick and reliable tool for pigment identification using both purified pigments and tattoo ink formulations. Some 36 organic pigments frequently used in tattoo inks were subjected to py-GC/MS with the aim to establish a pyrogram library. To cross-validate pigment identification, 28 commercially available tattoo inks as well as 18 self-made pigment mixtures were analyzed. Pyrograms of inks and mixtures were evaluated by two different means to work out the most reliable and fastest strategy for an otherwise rather time-consuming data review. Using this approach, the declaration of tattoo pigments currently used on the market could be verified. The pyrolysis library presented here is also assumed suitable to predict decomposition patterns of pigments when affected by other degradation scenarios, such as sunlight exposure or laser irradiation. Thus, the consumers’ risk associated with the exposure to toxicologically relevant substances that originate from pigment decomposition in the dermal layers of the skin can be assessed. Differentiation between more or less harmful pigments for this field of application now will become feasible.Electronic supplementary materialThe online version of this article (doi:10.1007/s00204-016-1739-2) contains supplementary material, which is available to authorized users.

Polybrominated diphenyl ethers in car dust in Nigeria: Concentrations and implications for non-dietary human exposure

In the present study, the levels of polybrominated diphenyl ethers in car dust samples collected from 12 randomly selected cars in Nigeria were measured, and the daily intake via dust ingestion were estimated for four categories of individuals. PBDEs were extracted and analyzed using ultra-sonication extraction and gas chromatography electron impact ionization mass spectrometry (GC-EIMS), respectively. The concentrations of ∑7PBDEs ranged from 159 to 736ngg−1 dry weight. BDE-209 was found to be the most prevalent congener with a total of 2130ngg−1, contributing up to 47% of the total congener values (4554ngg−1) and the other congeners contributed 53%. The mean and median concentrations of detected congeners ranged from 65 to 137 and 14 to 127ngg−1 dry weight, respectively. BDE-47 was detected in all the dust samples at a detection frequency of 100%, and this was followed by BDE-209 with 92%. The daily intake (DI) was estimated using concentrations corresponding to 5th percentile, median, and 95th percentile. The estimated DI was highest for professional drivers at 0.12ngkg−1 bw day−1 and this was followed by toddlers (0–3years) at 0.09ngkg−1 bw day−1 while DI estimate of 0.01ngkg−1 bw day−1 was determined for children (4–18years) and adults (>19years). PBDEs daily intake rates from car dust estimated in the present study are way below the USEPA reference dose (RfD) for oral exposure to PBDEs 47, 99, 153, and 209 of 100, 100, 200, and 7000ngkg bw day−1

Analysis of anonymized pooled urine in nine UK cities: variation in classical recreational drug, novel psychoactive substance and anabolic steroid use.

Analysis of anonymous pooled urine samples from street urinals has been used to demonstrate time-trends in the detection of classical recreational drugs and novel psychoactive substances (NPS). This study aimed to expand this to undertake a geographical trend analysis of classical recreational drugs/NPS across UK. Samples of anonymous pooled urine were collected from street urinals that had been in place for one night in April 2014 in nine cities across the UK. Collected samples were then analysed for the presence of recreational drugs, NPS anabolic steroids using high-performance liquid chromatography coupled to high-resolution accurate mass full-scan mass spectrometry and gas chromatography coupled to electron impact ionization mass spectrometry operating in selected ion monitoring and full-scan modes. Ten classical recreational drugs, nine NPS and four anabolic steroids were detected across the nine cities; the range of detection was from 1 in Leeds to 14 in London. The most common classical drugs were cocaine (9 cities) and 3,4-methylenedioxy-methamphetamine (8 cities); the most common NPS was 4-methylmethcathinone (5 cities). In addition there was variation in the detection of NPS, with methylhexaneamine detected only in Bristol and London, piperazines (3-trifluoromethylphenylpiperazine and 1-benzylpiperazine) and pentedrone only detected in Birmingham and the cathinone methylone only detected in London. There is variability in the detection of classical recreational drugs, NPS and anabolic steroids across UK, likely reflecting variation in their use. This technique can be used to supplement drug use surveys to determine geographical and time trends in the use of these substances. This is important to ensure appropriate targeting of drug-related interventions.

Multi-photon and electron impact ionisation studies of reactivity in adenine–water clusters

Multi-photon ionisation (MPI) and electron impact ionisation (EII) mass spectrometry experiments have been carried out to probe unimolecular and intermolecular reactivities in hydrated adenine clusters. The effects of clustering with water on fragment ion production from adenine have been studied for the first time. While the observation of NH4+ fragments indicated the dissociation of protonated adenine, the dominant hydration effects were enhanced C4H4N4+ production and the suppression of dissociative ionisation pathways with high activation energies. These observations can be attributed to energy removal from the excited adenine radical cation via cluster dissociation. Comparisons of MPI and EII measurements provided the first experimental evidence supporting hypoxanthine formation in adenine–water clusters via theoretically predicted barrierless deamination reactions in closed shell complexes.

Cross validation of gas chromatography-flame photometric detection and gas chromatography–mass spectrometry methods for measuring dialkylphosphate metabolites of organophosphate pesticides in human urine

We report two analytical methods for the measurement of dialkylphosphate (DAP) metabolites of organophosphate pesticides in human urine. These methods were independently developed/modified and implemented in two separate laboratories and cross validated. The aim was to develop simple, cost effective, and reliable methods that could use available resources and sample matrices in Thailand and the United States. While several methods already exist, we found that direct application of these methods required modification of sample preparation and chromatographic conditions to render accurate, reliable data. The problems encountered with existing methods were attributable to urinary matrix interferences, and differences in the pH of urine samples and reagents used during the extraction and derivatization processes. Thus, we provide information on key parameters that require attention during method modification and execution that affect the ruggedness of the methods. The methods presented here employ gas chromatography (GC) coupled with either flame photometric detection (FPD) or electron impact ionization-mass spectrometry (EI-MS) with isotopic dilution quantification. The limits of detection were reported from 0.10ng/mL urine to 2.5ng/mL urine (for GC-FPD), while the limits of quantification were reported from 0.25ng/mL urine to 2.5ng/mL urine (for GC-MS), for all six common DAP metabolites (i.e., dimethylphosphate, dimethylthiophosphate, dimethyldithiophosphate, diethylphosphate, diethylthiophosphate, and diethyldithiophosphate). Each method showed a relative recovery range of 94-119% (for GC-FPD) and 92-103% (for GC-MS), and relative standard deviations (RSD) of less than 20%. Cross-validation was performed on the same set of urine samples (n=46) collected from pregnant women residing in the agricultural areas of northern Thailand. The results from split sample analysis from both laboratories agreed well for each metabolite, suggesting that each method can produce comparable data. In addition, results from analyses of specimens from the German External Quality Assessment Scheme (G-EQUAS) suggested that the GC-FPD method produced accurate results that can be reasonably compared to other studies.

Fatty Acid Profile of the Initial Oral Biofilm (Pellicle): an In‐Situ Study

The first step of bioadhesion on dental surfaces is the formation of the acquired pellicle. This mainly acellular layer is formed instantaneously on all solid surfaces exposed to oral fluids. It is composed of proteins, glycoproteins and lipids. However, information on the lipid composition is sparse. The aim of the present study was to evaluate the fatty acid (FA) profile of the in-situ pellicle for the first time. Furthermore, the impact of rinses with safflower oil on the pellicle's FA composition was investigated. Pellicles were formed in situ on bovine enamel slabs mounted on individual upper jaw splints. The splints were carried by ten subjects over durations of 3-240min. After comprehensive sample preparation, gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS) was used in order to characterize qualitatively and quantitatively a wide range of FA (C12-C24). The relative FA profiles of the pellicle samples gained from different subjects were remarkably similar, whereas the amount of FA showed significant interindividual variability. An increase in FA in the pellicle was observed over time. The application of rinses with safflower oil resulted in an accumulation of its specific FA in the pellicle. Pellicle formation is a highly selective process that does not correlate directly with salivary composition, as shown for FA.

Enhancement of Gaseous Iodine Emission by Aqueous Ferrous Ions during the Heterogeneous Reaction of Gaseous Ozone with Aqueous Iodide

Gaseous I2 formation from the heterogeneous reaction of gaseous ozone with aqueous iodide in the presence of aqueous ferrous ion (Fe(2+)) was investigated by electron impact ionization mass spectrometry. Emission of gaseous I2 increased as a function of the aqueous FeCl2 concentration, and the maximum I2 formation with Fe(2+) was about 10 times more than without Fe(2+). This enhancement can be explained by the OH(-) scavenging by Fe(3+) formed from Fe(2+) ozonation to produce colloidal Fe(OH)3. This mechanism was confirmed by measurements of aqueous phase products using a UV-vis spectrometer and an electrospray ionization mass spectrometer. We infer that such a pH-buffering effect may play the key role in general halogen activations.

Theoretical and experimental study of the non-stoichiometric LinI (n = 3 and 5) clusters

The neutrals of the LinI (n=2–6) clusters were detected using Knudsen-cell which was placed into ionization chamber of the magnetic sector mass spectrometer. The first theoretical and experimental data on the Li3I and Li5I clusters were presented in this Letter. The ionization energies of the neutral of Li3I and Li5I clusters, obtained by the electron impact ionization mass spectrometry, were (5.14±0.25) and (4.62±0.25)eV, respectively. We report the geometry, ionization energies and thermodynamical stability of these clusters, calculated at the restricted coupled cluster RHF-RCCSD/cc-pVTZ(Li), cc-pVTZ-PP(I) level of theory.

A theoretical study of SnF2+, SnCl2+, and SnO2+ and their experimental search

We present a detailed theoretical study of the stability of the gas-phase diatomic dications SnF(2+), SnCl(2+), and SnO(2+) using ab initio computer calculations. The ground states of SnF(2+), SnCl(2+), and SnO(2+) are thermodynamically stable, respectively, with dissociation energies of 0.45, 0.30, and 0.42 eV. Whereas SnF(2+) dissociates into Sn(2+) + F, the long range behaviour of the potential energy curves of SnCl(2+) and SnO(2+) is repulsive and wide barrier heights due to avoided crossing act as a kind of effective dissociation energy. Their equilibrium internuclear distances are 4.855, 5.201, and 4.852 a(0), respectively. The double ionisation energies (T(e)) to form SnF(2+), SnCl(2+), and SnO(2+) from their respective neutral parents are 25.87, 23.71, and 25.97 eV. We combine our theoretical work with the experimental results of a search for these doubly positively charged diatomic molecules in the gas phase. SnO(2+) and SnF(2+) have been observed for prolonged oxygen ((16)O(-)) ion beam sputtering of a tin metal foil and of tin (II) fluoride (SnF(2)) powder, respectively, for ion flight times of about 10(-5) s through a magnetic-sector mass spectrometer. In addition, SnCl(2+) has been detected for (16)O(-) ion surface bombardment of stannous (tin (II)) chloride (SnCl(2)) powder. To our knowledge, SnF(2+) is a novel gas-phase molecule, whereas SnCl(2+) had been detected previously by electron-impact ionization mass spectrometry, and SnO(2+) had been observed before by spark source mass spectrometry as well as by atom probe mass spectrometry. We are not aware of any previous theoretical studies of these molecular systems.