Mass-spectrometric study of the cyclization of diazo compounds. 10. 2-Diazomalonic acid amides. Mass spectra of the negative ions

The mass spectra of the negative ions of the dissociative resonance capture of electrons of diazo amides and the isomeric triazoles were studied. The molecular negative ions of these compounds are unstable and do not undergo interisomerization. The principal fragmentation process involves the elimination of a molecule of nitrogen and transformation of the resulting [M-N₂]^– ions to the heterocyclic form, which is the same for the two isomers.See [1] for communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–944, July, 1987.     

Studies in cluster ion formation. Part I. Fast atom bombardment mass spectrometry of tetraalkylammonium halides: Factors influencing cluster ion size and stability

Positive and negative ion fast atom bombardment mass spectra of tetraalkylammonium halide salts (NR₄X, where X = Cl, Br, I and NR₄ = NMe₄, NEt₄) have been studied and intense cluster ion formation has been observed. The cluster ion intensity distributions were found to show enhancements at certain cluster numbers (n). The negative cluster ions of NMe₄X salts showed anomalous ion intensity regions, which differed from both the positive cluster ions of all NR₄X salts and also the corresponding negative clusters of NEt₄X salts. The influence of anion and cation size on cluster ion formation and abundances has been studied and it has been established that smaller anion and cation size favours the formation of larger cluster ions. The possible structures of the cluster ions exhibiting relative increased stabilities are discussed.     

The thermochemical characteristics of the LnCl<Superscript>−</Superscript><Subscript>4</Subscript> and Ln<Subscript>2</Subscript>Cl<Superscript>−</Superscript><Subscript>7</Subscript> negative ions

The literature data on the thermochemical characteristics of negative LnCl^? ₄ and Ln₂Cl^? ₇ ions (from lanthanum to lutetium inclusive) in the gas phase are systematized. The enthalpies of ion-molecular and ion-ion reactions with the participation of these ions were calculated and used to determine the enthalpies of formation of the ions for the whole lanthanide series.     

O2气中激光烧蚀Ta2O5产物离子的氧化反应

Ta2O5薄膜作为电容元件材料的替代品已在微电子等领域中显示出广阔的应用前景[1]．脉冲激光沉积（PLD）法制备Ta2O5薄膜以其显著的优点引起了广泛重视[2，3]．而对激光烧蚀的物理化学过程的认识是完善这一方法的重要前提．我们曾采用时间分辨与角分辨飞行四极质谱[4]和发光光谱技术[5]较系统地研究了激光烧蚀Ta2O5产生的羽状物的组成和特征，并认为在O2气氛中沉积Ta2O5薄膜可以改善甚至避免形成缺氧的薄膜．但由于上述实验方法上的限制，未能详细考察激光烧蚀Ta2O5生成的离子产物在O2气氛中发生的氧化反应．为了研究激光烧蚀产物离子…     

MALDI-MS/MS with Traveling Wave Ion Mobility for the Structural Analysis of N-Linked Glycans

The preference for singly charged ion formation by MALDI makes it a better choice than electrospray ionization for profiling mixtures of N-glycans. For structural analysis, fragmentation of negative ions often yields more informative spectra than fragmentation of positive ones but such ions are more difficult to produce from neutral glycans under MALDI conditions. This work investigates conditions for the formation of both positive and negative ions by MALDI from N-linked glycans released from glycoproteins and their subsequent MS/MS and ion mobility behaviour. 2,4,6-Trihydroxyacetophenone (THAP) doped with ammonium nitrate was found to give optimal ion yields in negative ion mode. Ammonium chloride or phosphate also yielded prominent adducts but anionic carbohydrates such as sulfated N-glycans tended to ionize preferentially. Carbohydrates adducted with all three adducts (phosphate, chloride, and nitrate) produced good negative ion CID spectra but those adducted with iodide and sulfate did not yield fragment ions although they gave stronger signals. Fragmentation paralleled that seen following electrospray ionization providing superior spectra than could be obtained by PSD on MALDI-TOF instruments or with ion traps. In addition, ion mobility drift times of the adducted glycans and the ability of this technique to separate isomers also mirrored those obtained following ESI sample introduction. Ion mobility also allowed profiles to be obtained from samples whose MALDI spectra showed no evidence of such ions allowing the technique to be used in conditions where sample amounts were limiting. The method was applied to N-glycans released from the recombinant human immunodeficiency virus glycoprotein, gp120.     

Negative-ion mass spectra of some N-mesyl derivatives of o-(cycloalk-2-enyl)-, o-(cycloalk-1-enyl)-, o-(pent-2-enyl)-, o-dibromopentylanilines and (α-bromoalkyl)indolines

The formation and fragmentation of negative ions of some N-(methylsulfonyl)anilines upon resonance electron capture have been studied. The formation of long-living molecular ions is due to the presence of the mesyl groups in the molecules. The difference in negative-ion mass spectra of isomeric N-(methylsulfonyl)anilines has been revealed.     

Thermochemical determination of structure of negative ions on the basis of data from resonance electron capture mass spectrometry. 1. Heterocyclic analogs of cyclopentadiene

Appearance energies have been measured for negative ions formed in the gas phase upon dissociative capture of electrons by molecules of cyclopentadiene, pyrrole, selenophene, thiophene, furan, and furan derivatives. From an analysis of the enthalpies of formation of the fragmentation products, it has been established that electron capture by molecules of C₄H₄X (X=O, S, Se, NH, CH₂) leads to the formation of ions with cyclic and acyclic structures.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 590–592, March, 1991.     

Resonant dissociative electron capture by the simplest amino acids and dipeptides

The formation of ions from amino acids (glycine and alanine) and dipeptides (glycylglycine, alanylalanine, and glycylalanine) under the resonant electron capture conditions was studied by negative ion resonant electron capture mass spectrometry. The isobaric ions were found, their effective yield curves were experimentally separated, and the elemental composition was determined. The thermochemical aspect of ion formation was considered, and probable dissociative channels of fragmentation ion formation and their structures were established on the basis of this aspect. Bond cleavage reactions only and H-shift processes were revealed. The rearrangements occur presumably through the stage of formation of intramolecular hydrogen bonds. The cross-sections of formation of ions [M − H]⁻ were measured in the energy range 1.1–1.3 eV. The metastable decay channels of ions [M − H]⁻ and [M − COOH]⁻ were found in the energy range 4.5–7.5 eV for dipeptides, which enabled establishing the genetic relationship between the parental and daughter ions and revealing hidden fragmentation pathways.     

Formation and dissociation of the chloroethylene anions

Electron attachment spectroscopy is employed to study the formation of negative ions from the chloroethylenes. It is found that the resonances recently observed in the total electron scattering cross section are predominantly associated with the formation of Cl^?. Only in tetrachloroethylene is a long-lived parent negative ion observed.     

Dissociative electron attachment to glycyl-glycine, glycyl-alanine and alanyl-alanine

The processes of negative ions formation of dipeptides glycyl-glycine, glycyl-alanine and alanyl-alanine in the conditions of resonant electron capture have been studied with a help of negative ions mass spectrometry. Using a thermochemical approach, the main channels of fragment negative ions formation were found and the structure of the ions were established. The isobaric ions have been identified by the experiments with high mass resolution. The cross sections of fragment ions formation were measured. The metastable fragmentation of [M-H](-) and [M-COOH](-) ions in the energy range 4.5-7.5 eV have been found.     

SN2 reactions in the gas phase. Structure of the transition state

The alkylhalide-halide association ions, [RX₂]^? that are observed in the negative chemical ionization mass spectra of alkyl halides appear to be directly related to the corresponding S_N2 transition states in solution. ‘Frontside’ association of halide ions with bridgehead alkyl halides does not occur in our system. The Change in heats and entropies of association for the chloromethane series is consistent with delocalization in the [RX]₂^? ions.     

Detection of negative ions in glow discharge mass spectrometry for analysis of solid specimens

A new method is presented for elemental and molecular analysis of halogen-containing samples by glow discharge time-of-flight mass spectrometry, consisting of detection of negative ions from a pulsed RF glow discharge in argon. Analyte signals are mainly extracted from the afterglow regime of the discharge, where the cross section for electron attachment increases. The formation of negative ions from sputtering of metals and metal oxides is compared with that for positive ions. It is shown that the negative ion signals of F^? and TaO₂F^? are enhanced relative to positive ion signals and can be used to study the distribution of a tantalum fluoride layer within the anodized tantala layer. Further, comparison is made with data obtained using glow-discharge optical emission spectroscopy, where elemental fluorine can only be detected using a neon plasma. The ionization mechanisms responsible for the formation of negative ions in glow discharge time-of-flight mass spectrometry are briefly discussed.     

碳酸酯类电解液中Mg(NO3)2添加剂抑制锂枝晶生长的研究

在锂-硫化聚丙烯腈电池体系中,负极锂枝晶的形成和生长严重恶化了电池充放电性能,并给电池带来了安全隐患。而在更有利于稳定正极硫化聚丙烯腈材料的碳酸酯类电解液中,锂枝晶生长尤为严重。本文通过将硝酸镁添加到碳酸酯类电解液中,研究硝酸根和镁离子对锂金属表面改性的共同作用。实验数据发现,在硝酸根和镁离子共同作用下,锂枝晶生长被有效抑制。当硝酸镁浓度为100 mmol·L^-1时,锂铜半电池的库仑效率明显提高,并显著改善了锂-硫化聚丙烯腈电池的循环性能。300次循环后容量保持率为71%,远高于硝酸锂的61%和无添加剂的50%。     

Resonance electron capture by aniline molecules and its derivatives

Processes of the formation of negative ions from aniline and its derivatives were studied by the resonance electron capture technique. The results were compared with those obtained earlier for molecules of benzene, phenol, and chlorophenols. It was concluded that the processes of formation of negative ions in aniline differ substantially from those in benzene and phenol. The triplet series of resonances beginning from the resonance at 2.6 eV is observed.     

Ion/Molecule reactions in SiH4/H2S and GeH4/H2S mixtures

The gas phase ion chemistry of silane/hydrogen sulfide and germane/hydrogen sulfide mixtures was studied by ion trap mass spectrometry (ITMS), in both positive and negative ionization mode. In positive ionization, formation of X/S (X = Si, Ge) mixed ions mainly takes place via reactions of silane or germane ions with H₂S, through condensation followed by dehydrogenation. This is particularly evident in the system with silane. On the other side, reactions of H_nS₂⁺ ions with XH₄ (X = Si, Ge) invariably lead to formation of a single X? S bond. In negative ionization, a more limited number of mixed ion species is detected, but their overall abundance reaches appreciable values, especially in the SiH₄/H₂S system. Present results clearly indicate that ion processes play an important role in formation and growth of clusters eventually leading to deposition of amorphous solids in chemical vapor deposition (CVD) processes. Copyright © 2009 John Wiley & Sons, Ltd.     

On the structure of negative ions formed by dissociative electron attachment by monochlorophenol molecules

The energetics of negative ion formation by resonant dissociative electron attachment by o-, m-, and p-chlorophenol molecules was studied. The structures of some fragment ions and their neutral partners were established. Hidden rearrangement processes leading to the formation of oxy anions by the detachment of chlorine atoms from molecular ions were found. The O—H bond dissociation energies for o-, m-, and p-chlorophenol molecules were 3.74±0.11, 3.72±0.17, and 3.94±0.11 eV, respectively.     

原子簇正负离子的统计分布与生成机理

在分析了实验记录的大量原子簇离子质谱的基础上，发现原子簇的正负离子通常表现为不同的统计分布形式．将它们的分布形式与求解动力学方程得出的分布函数相比，发现由此反映了原子簇正负离子的不同的生成机理：实验所检测的原子簇正离子在许多情况下仅经历了聚合与解离反应，主要是中性原子簇分子电离后的产物；而相应的原子簇负离子则是经历了一系列离子一分子反应后的产物．     

Formation of Negative Hydrogen Ions in a Ne–H2 Hollow Cathode Discharge

The formation of negative hydrogen ions in a conventional hollow cathode discharge has been investigated. A mixture of Ne and H₂ proved to be more advantageous compared to pure hydrogen. The study has been performed by solving the electron Boltzmann equation, coupled with a system of balance equations for neon and hydrogen neutral and charged particles. The vibrational distribution function of hydrogen has been calculated. Our calculations show unusually high population of vibrationally excited hydrogen molecules in a Ne–H₂ mixture, which explains the high density of negative hydrogen ions under optimal conditions (total gas pressure of few Torr, hydrogen number mole fraction of 1–10% and discharge current of 10–100 mA). Line intensities originating from highly excited neon states vs. hydrogen pressure have been calculated and a comparison with existing experimental results has been made.     

About the plausible contribution of field ionization in the mechanism of the formation of dyes of ions under conditions of laser desorption/ionization from a nanostructurized graphite surface

An approach is proposed for the estimation of the contribution of field ionization (FI) to the mechanism of dye ion formation under the conditions of laser desorption/ionization (LDI) from a nanostructurized graphite surface. As test systems, rough graphite layers with dyes, e.g., imidazophenazine derivatives applied to them were chosen; these ensure FI in a strong electric field. The dyes form three neutral precursors upon reduction and various types of ions in different ionization methods. It was found that the mass distribution within the group of peaks formed by the initial dye molecule and the products of its reduction in the positive ion mode upon LDI from a rough graphite surface is shifted to lower masses by one atomic mass unit in comparison to the distribution recorded for LDI from a smooth metal support. The analysis of plausible pathways of ion formation has shown that such a shift may be due to the superposition of ions formed by the FI mechanism on a graphite substrate with a number of ions formed by protonation in LDI with no dependence on the support type. In the negative ion mode, the registration of LDI dye spectra succeeded only if the graphite substrates used favored negative FI and electron emission enhanced by the field.     

Reactions of [aryloxy(phenyl)carbene]pentacarbonylchromium(0) complexes with thiolate ions. Decreasing reactivity with increasing basicity of the nucleophile

A kinetic study of the reactions of thiolate ions with three Fischer-type [aryloxy(phenyl)carbene]pentacarbonyl chromium(0) complexes in 50% MeCN-50% water (v/v) is reported. Br?nsted plots of the second-order rate constants are biphasic with an initial steep rise for weakly basic thiolate ions (beta(nuc) approximately equal to 1.0) followed by a slightly descending leg with a negative slope (beta(nuc) approximately equal to -0.2) for strongly basic thiolate ions. This indicates a change from rate-limiting leaving group departure at low pK(RSH)(a) to rate-limiting nucleophilic attachment at high pK(RSH)(a). The negative beta(nuc) values result from a combination of minimal progress of C-S bond formation at the transition state and the requirement for partial desolvation of the nucleophile before it enters the transition state. Possible factors that may affect the degree of bond formation in reactions of Fischer carbene complexes as well as reactions of other unsaturated electrophiles with thiolate ions are discussed.