Neutralization-reionization Mass Spectrometry Research Articles

Combined quantum chemical and mass spectrometric study of [Si,C,H3,O]+isomers

The potential energy surface of [Si,C,H3,O]+ has been explored by means of ab initio MO calculations at the G2 level of theory as well as by mass spectrometric techniques. The silicon–methoxide cation H3COSi+ has been identified as the global minimum (ΔfH= 151 kcal mol–1), followed by the silaacetyl cations H3SiCO+(ΔfH= 172 kcal mol–1) and H3CSiO+(ΔfH= 180 kcal mor–1). A number of other intermediates, the transition structures associated with the mutual interconversion reactions and the energetics of possible fragmentation channels are explored computationally. It turns out that the energy demands for the unimolecular isomerizations of most of the isomers are substantially lower than those of fragmentations. Consequently, an identification of the different isomers based solely on mass spectrometric information is made difficult by intramolecular rearrangements which precede the structure-indicative fragmentation reactions, even though H3SiCO+ is clearly distinguishable from H3CSiO+ and H3COSi+. However, when the experimental findings are combined with the computationally predicted [Si,C,H3,O]+ potential-energy surface and with thermochemical information, this difficulty can be overcome, and a coherent picture of this complex system emerges. In addition, the existence of the neutral radicals H3COSi˙, H3CSiO˙, as well as H3SiCO˙ and/or H3SiOC˙ is explored by means of neutralization–reionization mass spectrometry.

The structure of C 5H 5RFe + (R = F, Cl, Br, I, O, OH, OCH 3, C 6H 5, H) ions in the gas phase and the generation of their neutral counterparts by neutralization-reionization mass spectrometry

The structure of C5H5FeR(+·) ions was studied by tandem mass spectromerry that included the neutralization-reionization (NR) method. Halogen-containing species (R = F, Cl, Br, I) showed fragmentation that was consistent with a structure that has the cyclopentadienyl ring and R as separate ligands at the metal atom (structure A). This structure also was identified for C5H5FeO(+) and CpFeOH(+·) ions, but these species also easily isomerized to metal-cyclopentadiene structure, RC5H5Fe(+·) (B), followed by hydrogen rearrangement(s) and CO loss. B was the dominant structure of C5H5FeH(+·) and C5H5FeC6H 5 (+·) ions. All ions that have structure A showed recovery signals in their NR mass spectra that indicated that their stable neutral counterparts were generated. The NR mass spectra also provided complementary information about the structure of ions before neutralization and after reionization.

Hydrogen bonding in transient bifunctional hypervalent radicals by neutralization—reionization mass spectrometry

Neutralization-reionization mass spectrometry is used to generate hypervalent 9-N-4 (ammonium) and 9-O-3 (oxonium) radicals derived from protonated α,ω-bis-(dimethylamino)alkanes and α,ω-dimethoxyalkanes, which exist as cyclic hydrogen-bonded structures in the gas phase. Collisional neutralization with dimethyl disulfide, trimethylamine, and xenon of the hydrogen-bonded onium cations followed by reionization with oxygen results in complete dissociation. Bond cleavages at the hypervalent nitrogen atoms are found to follow the order CH2-N>CH3-N>N-H, which differs from that in the monofunctional hydrogen-n-heptyldimethylammonium radical, which gives CH2-N>N-H>CH3-N. No overall stabilization through hydrogen bonding of the bifunctional hypervalent ammonium and oxonium radicals is observed. Subtle effects of ring size are found that tend to stabilize large ring structures and are attributed to intramolecular hydrogen bonding.

Characterization of the C 3H 6O +. ion from 2-methoxyethanol. Mixture analysis by dissociation and neutralization—reionization

The C3H6O(+·) ion formed upon the dissociative ionization of 2-methoxyethanol is identified by a combination of several tandem mass spectrometry methods, including metastable ion (MI) characteristics, collisionally activated dissociation (CAD), and neutralization-reionization mass spectrometry (NRMS). The experimental data conclusively show that 2-methoxyethanol molecular ion, namely, HOCH2CH2OCH 3 (+·) , loses H2O to yield mainly the distonic radical ion ·CH2CH2OCH 2 (+) along with a smaller amount of ionized methyl vinyl ether, namely, CH2=CHOCH 3 (+·) . Ring-closed products, such as the oxetane or the propylene oxide ion are not observed. The proportion of ·CH2CH2OCH 2 (+) increases with decreasing internal energy of the 2-methoxyethanol ion, which indicates a lower critical energy for the pathway leading to this product than for the competitive generation of CH2=CHOCH 3 (+·) . The present study also uses MI, CAD, and NRMS data to assess the structure of the distonic ion(+) (CH3)CHOCH2· (ring-opened ionized propylene oxide) and evaluate its isomerization proclivity toward the methyl vinyl ether ion.

Polycarbon Disulfides SCnS (n = 1-3) and Their Protonated and Methylated Forms (HCnS2+ and CH3CnS2+): Tandem Mass Spectrometry and ab Initio MO Study

Dissociative ionization of 4,5-bis(methylthio)-1,2-dithiole-3-thione (1) has allowed the detection of a series of carbon disulfide radical cations, SCnS.+ (n = 1-3), and their S-methylated forms, CH3SCnS+, in the gas phase of a mass spectrometer. The connectivities and stabilities of these ions and the corresponding neutrals have been probed by collisional activation (CA) and neutralization-reionization (NR) mass spectrometry. Moreover, the sites of protonation and cationic methylation of the polycarbon disulfides have been investigated by a combination of flash vacuum pyrolysis, chemical ionization, and CAMS (FVP/CI/MS/MS). The experimental results are supported by ab initio MO calculations at the QCISD(T)/6-311+G(2d,p) + ZPVE level. Both experiments and calculations indicate that the most favorable site of protonation and methylation is the carbon atom for C2S2 and C3S2 but a sulfur atom for CS2. The proton affinities (298 K) of C2S2 and C3S2 are predicted to be 842 and 818 kJ mol(-1), respectively.

THE PHOSPHOROTRITHIOUS ACID (HS)3P IS STABLE IN THE DILUTE GAS PHASE

Abstract Using the technique of neutralization-reionization mass spectrometry (NRMS) it could be shown that the elusive phosphorotrithious acid (HS)3P is a stable molecule in the rarefied gas phase. A triple propene elimination from the molecular ions of the dipropyl ester of propylphosphonotrithioic acid, PrP(S)(SPr)2, (70 eV EI) yields m/z 130 radical cations of composition “[H3PS3] +”. Analysis of their collisional activation (CA) mass spectrum using thermochemical data, shows that these “[H3PS3] +” ions have the structure [(HS)3P] + rather than that of the tautomer [(HS)2P(=S)H| +. Subjected to a NRMS experiment, these ions retain their structure and are cleanly reduced to (HS)3P. The results are entirely compatible with ab initio MO-calculations executed at the HF/3-21G∗ and HF/6-31G∗∗ levels of theory (GAUSSIAN 92 system of programs). The calculations predict that [(HS)3P] + and [(HS)2P(=S)H] + and their respective neutral counterparts are local minima which are separated by high potential energy ba...

Gas‐Phase Activation of Fluorocarbons by “Bare” and Coordinated Praseodymium Cations

Rather than CH or CC bonds, Pr+ activates CF bonds in the gas phase in a variety of aliphatic and aromatic fluorocarbons; PrF+ and PrO+ react analogously. This first general example of preferential CF bond activation in the gas phase allows interesting conclusions to be drawn regarding the importance of 4f electrons for the reactivity of isolated lanthanide species. The existence of neutral PrF and PrF2 in the gas phase was also proven by neutralization–reionization mass spectrometry (NRMS).

Letter: The generation and characterization of neutral silaethene by neutralization–reionization mass spectrometry

Letter: The generation and characterization of neutral silaethene by neutralization–reionization mass spectrometry

Polycarbon sulfides CnS (n = 2–6) and corresponding hydrides HCnS.. Neutralization–reionization mass spectrometry and ab initio molecular orbital study

AbstractA series of polycarbon sulfide radical cations, CnS+· (n = 2–6), have been detected in the 70 eV electron impact mass spectrum of benzothiazole. Application of collisional activation and neutralization–reionization mass spectrometry indicates their connectivity and the stability of the corresponding neutral molecules CnS in the gas phase. Closed shell HCnS+ ions (n = 2–6) and the corresponding radicals HCnS. have similarly been identified in the dilute gas phase of the mass spectrometer. The experimental results are supported by ab initio molecular orbital calculations at the QCISD(T)/6–311G** (based on additivity approximation) + ZPVE level.

Dissociation characteristics of [M + X] + ions (X = H, Li, Na, K) from linear and cyclic polyglycols

The unimolecular reactions of protonated and metalated polyglycols with kiloelectronvolt translational energies have been studied by collisionally activated dissociation and neutralization-reionization mass spectrometry. The former method provides information on the ionic dissociation products, whereas the latter allows for the identification of the complementary neutral losses. Protonated linear polyglycols mainly undergo charge-initiated decompositions that lead to eliminations of smaller oligomers. On the other hand, protonated crown ethers (“cyclic” polyglycols) favor charge-induced reactions that proceed by cleavages of two ethylene oxide units in the form of 1,4-dioxane. Replacement of one O by NH in the crown ether dramatically changes its unimolecular chemistry; now, charge-remote 1,4-eliminations from ring-opened isomers are preferred. Charge-remote reactions are also the major decomposition channels of all metalated precursors studied. The linear polyglycols decompose primarily by 1,4-H 2 eliminations and to a lesser extent by homolytic cleavages near chain ends. The reverse is true for metalated crown ethers, which preferentially produce distonic radical cations by the loss of saturated radicals; these reactions are proposed to involve prior rearrangement to open-chain isomers. The nature of the metal ion (Li +, Na +, or K +) does not greatly affect the unimolecular chemistry of the cationized polyglycol. In general, metalated precursors form many abundant fragment ions over the entire mass range; hence, collisional activation of such ions at high kinetic energy should be particularly useful for structure elucidations.

Internal energy distributions of tungsten hexacarbonyl ions after neutralization-reionization

The internal energy distributions P(ϵ) transferred to W(CO) + 6 during the kiloelectronvolt collisions that occur upon neutralization-reionization (NR) have been estimated based on the relative abundances of the W(CO) + 0−6 products present in NR spectra (thermochemical method). The average internal energy of the incipient W(CO) + 6 * ions arising after near thermoneutral neutralization with trimethylamine followed by reionization with O 2 is −9 eV for 8-keV precursor ions and is mainly deposited during reionization. For comparison, the mean internal energy of W(CO) + 6* after electron ionization (EI) or collisionally activated dissociation (CAD) is −6 eV. Making the neutralization step endothermic slightly increases the overall excitation gained; however, a large increase in endothermicity ( > 16 eV) causes only a modest rise of the average internal energy (< 2 eV). The P(ϵ) curve for NR increases exponentially up to ∼ 6 eV and levels off at higher energies, showing that the probability of imparting large internal energies (6–17 eV) is high. In sharp contrast, the most probable excitation on CAD is ≤ 6 eV, and the probability of deposition of larger energies declines exponentially. The mean internal energies after CAD and NR decrease steadily when the kinetic energy is lowered. The structure (minima-maxima) observed in the P(ϵ) distribution for EI, which most likely originates from Franck-Condon factors, is not reproduced in the distributions for NR or high energy CAD, despite the fact that all three methods involve electronic excitation. Because of the large internal energies transferred upon NR, NR mass spectrometry could be particularly useful in the differentiation of ionic isomers with high dissociation but low isomerization thresholds. ( J Am Soc Mass Spectrom 1994, 5, 1093-1101)

Neutralization-reionization mass spectrometry: a powerful "laboratory" to generate and probe elusive neutral molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNeutralization-reionization mass spectrometry: a powerful "laboratory" to generate and probe elusive neutral moleculesNorman Goldberg and Helmut SchwarzCite this: Acc. Chem. Res. 1994, 27, 11, 347–352Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://doi.org/10.1021/ar00047a005RIGHTS & PERMISSIONSArticle Views309Altmetric-Citations175LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (831 KB) Get e-Alerts Get e-Alerts

The thionitroxyl free radical (H2NS) and its ionic counterparts (H2NS+ and H2NS−): A theoretical and experimental study

An experimental and theoretical characterization has been carried out for the thionitroxyl radical (H2NS) and its ionic counterparts (H2NS)+ and (H2NS)−. Experimentally, (H2NS)+ and (H2NS) have been detected by a combination of collisional activation and neutralization-reionization mass spectrometry. Thiourea has been used as a precursor. Theoretically, the neutral and ionic potential energy surfaces have been explored using (PU)MP4/6-311++G(3df,2p) energies based on (U)MP2/6-311++(d,p) geometries. Predictions for some spectroscopic and thermochemical properties have been made on the basis of molecular orbital calculations and empirical corrections. The rearrangements leading to the (HNSH) and (NSH2) isomeric species and the loss of hydrogen or other fragmentations have also been examined. The (HNSH) and (NSH2) species are less stable than their respective thionitroxyl isomers in all states considered. For the (H2NS)+ cation, an H loss constitutes the lowest energy fragmentation followed by an H2 elimination giving NS+ and a cleavage of the N–S bond. The thermochemical data are predicted as follows: ΔH0f,0 (H2NS)=31.2±3 kcal/mol, IEa(H2NS)=88.±0.2 eV, EAa(H2NS)=1.4±0.2 eV, PA(H2NS−)=357.5±3 kcal/mol as compared with the experimental value of 356.8±3 kcal/mol, ΔH0f,0(HNS)=52.6±3 kcal/mol and ΔH0f,0(H2NSH)=13.4±3 kcal/mol.

Unimolecular neutral and ion kinetics by variable‐time neutralization—reionization mass spectrometry

AbstractA new method is described for the determination of rate parameters of unimolecular dissociations of neutral intermediates and ions produced by collisional neutralization and reionization at kiloelectronvolt kinetic energies. The method utilizes variable time‐scales for neutral and ion dissociations to obtain time‐dependent survivor and product ion yields. Kinetic analysis then provides phenomenological rate constants for both neutral and ion dissociations. Neutralization with CH3I, NO, (C2H5)2O, C6H6 and Xe of methyl iodide cation radicals is shown to produce the intermediate neutral molecules with different internal energies, resulting in different rates of neutral and ion dissociations. Vibrational excitation in neutralized CH3I results in neutral dissociations with rate parameters in the (1–3) × 105 s–1 range. The origin of neutral excitation by fast collision is explained by the intermediate formation of highly excited Rydberg states that decay by photon emission to the vibrationally excited ground state of the molecule.

The Intriguing Diversity of Neutral and Cationic Selenium-Nitrogen Heterocycles

Abstract Salts containing ternary Se,N,Cl cations, [(SeCl)2N]+X− (X− = SbCl6 −, 1; FeCl4 −, 2) and [(SeCl2)2N]+Y− (Y− = AsF6 −, 3), were prepared by reaction of N(SiMe3)3 with [SeCl3]+X− or [SeCl3]+Y−, respectively. In addition, 1 was formed from the reaction of Se2NCl3 with SbCl5. The structures of 1–3 were determined by X-ray crystallography. Reaction of 1 with F3C-C[tbnd]C-CF3 led to the formation of the novel five-membered heterocyclic cation . Compound 4 turned out to be a useful building block to generate new selenium containing heterocycles such as the neutral rings (7π radical) (5), (6) and (7). The heterocycle 6 was shown by electron diffraction studies to have a close to planar four-ring structure. The solid state structure of compound 7 was determined by X-ray crystallography. The existence of the neutral radical 5 was established by means of neutralization-reionization mass spectrometry. The structures of 6 and of the cation in 4 were computed ab initio using model compounds in which the CF3 g...

The unimolecular chemistry of quaternary ammonium ions and their neutral counterparts

The quaternary ammonium ions (CH 3) 4N + ( 1 +), (CH 3CH 2) 4N + ( 2 +), C 6H 5N + (CH 3) 3( 3 +), C 6H 5CH 2N + (CH 3) 3 ( 4 +) and C 6H 5CH 2N + (CH 2CH 3) 3 ( 5 +) and the corresponding ammonium radicals 1–5 have been studied in the gas phase by metastable ion (MI) characteristics, collisionally activated dissociation (CAD) and neutralization—reionization mass spectrometry (NRMS). The unimolecular chemistry of the ammonium ions is influenced by the nature of their substituents (R). Based on cations 3 +– 5 +, which carry different types of N +R bonds, preferential dissociation at N +—benzyl > N +—alkyl > N +—phenyl takes place. The two major fragmentation channels observed for all ions are (i) direct cleavage of the N +R bond with charge retention on the species of lowest ionization energy and (ii) formation of an immonium ion by loss of the hydrocarbon RH (from all cations) or RCH 3 (only from 2 + and 5 +). These decompositions proceed after initial, rate-determining isomerization of 1 +–5 + to ion/dipole complexes R 3N + / R or, in case of benzyl substitution, to R +/NR 3. The NRMS experiments reveal that the hypervalent radicals 1–5 are unstable, decaying within ⪡ 0.2 μs by rupture of one of the NR bonds. 3–5 mainly cleave the NR bond which yields the thermodynamically most stable products.

A neutralization—reionization (NR) case study for cationic iron complexes with simple ligands: NR mass spectra of Fe(C 2H 4) + and Fe(CO) +

The cationic iron(I) complexes Fe(C 2H 4) + and Fe(CO) + were examined by neutralization—reionization mass spectrometry (NRMS). Whereas the NR mass spectrum of the carbonyl complex exhibits a signal corresponding to the reionized neutral molecule Fe(CO), for the neutral Fe(C 2H 4) complex no recovery signal is observed; rather, in the course of the experiment the complex dissociates to Fe and C 2H 4. An explanation for this seemingly contradictory behaviour of structurally related metal complexes in a NR process is provided by ab initio MO calculations, in which the geometries of Fe(C 2H 4) + ( 4B 2), Fe(C 2H 4) ( 5B 2), Fe(CO) + ( 4Σ −, Fe(CO) ( 3Σ −, and Fe(CO) ( 5Σ −) have been fully optimized at the QCISD(T) level of theory. From the theoretical results, a neutralization-reionization scheme for organometallic ions MX + emerges which considers the effects caused by curve-crossing from a bound state to a repulsive ground-state asymptote of the neutral building blocks M and X. Thus, even for bound organometallic complexes MX, recovery signals in the NR mass spectrum can only be detected if the internal energy deposited in MX in the vertical electron-transfer reaction MX + → MX is too small to permit this curve-crossing. If dissociation occurs on the time scale of the NR experiments, the spectrum exhibits features of both the metal M and the ligand X, thus revealing the structural properties of the (organic) ligand X bound to the metal ion.

Protonated Forms of Iminopropadienones, RN:C:C:C:O, and Cyanoketenes: Combined ab initio MO and Mass Spectrometry Studies

The structures and unimolecular fragmentation reactions of protonated iminopropadienones, RN=C=C=C=O (R=H and CH3), were investigated by a combination of mass spectrometry based experiments (collisional activation (CA), neutralization-reionization (NR), and chemical ionization (CI) mass spectrometry and flash vacuum pyrolysis) and high-level ad initio molecular orbital calculations, at the QCISD(T)/6-311+G(2d,p) level of theory. The C- and N-protonated forms, RN(+)=C-CH=C=O and R(HN+=C=C=O, were separately generated from a variety of precursors. The experiments and calculations indicate that the most favorable site of protonation of iminopropadienones is the central carbon atom (C-2), and the resulting ions are best regarded as N-alkylated or N-protonated cyanoketenes. The N-protonated iminopropadienone is close in energy to the C-protonated one, while the O-protonated form is significantly higher in energy. The proton affinities (298 K) of HNCCCO, CH3NCCCO, NCCECO, and NCC(CH3)CO are predicted to be 861, 920, 784, and 798 kJ mol(-1), respectively.

Iminoethenethiones, RN:C:C:S: Characterization by Neutralization-Reionization Mass Spectrometry and G2(MP2) Theory

(Methylimino)ethenethione (2) and iminoethenethione (4) are stable molecules on the microsecond time scale of neutralization-reionization mass spectrometry experiments. The corresponding radical cations were generated by fragmentation of thiazolopyrimidinedione molecular ions 1(.+) and 3(.+). Iminoethenethione (4) does not tautomerize to thioformyl cyanide (H-CS-CN, 5) under the wall-less conditions of the MS experiment, but it does so under FVP conditions when generated from isoxazolones 6. Thioformyl cyanide was unequivocally identified by IR and mass spectra. The structures and stabilities of 2, 4, and 4(.+) were investigated by ab initio calculations at the G2(MP2) level of theory. Both 2 and 4 are predicted to have a singlet ground state, in contrast to O double bond C double bond C double bond S, for which a triplet state is preferred. The singlet-triplet gaps are approximately 40 kJ mol(-1). In agreement with experimental findings, both iminoethenethiones are calculated to be thermodynamically and kinetically stable species, lying in energy wells with at least a 100 kJ mol(-1) barrier to dissociation into HNC (or CH3NC) + CS. The IR and UV spectra and ionization energies of 2 and 4 are predicted. The iminoethenethione radical cation (4(.+)) is found to be the global minimum on the C2HNS.+ potential energy surface and stable toward all possible fragmentations: the most favorable fragmentations into H-. + NCCS+ and HNC + CS.+ are in accord with the mass spectrometric observations.

Experimental Evidence for the Existence of Cyanovinylidene :C:C(H)CN. Gas-Phase Characterization of a Possible Interstellar Molecule

Experiments on the first successful gas-phase generation of the theoretically predicted cyanovinylidene:C=C-(H)CN are reported by applying the technique of neutralization-reionization mass spectrometry