首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 656 毫秒
1.
Hydration of alkylammonium ions under nonanalytical electrospray ionization conditions has been found to yield cluster ions with more than 20 water molecules associated with the central ion. These cluster ion species are taken to be an approximation of the conditions in liquid water. Many of the alkylammonium cation mass spectra exhibit water cluster numbers that appear to be particularly favorable, i.e., “magic number clusters” (MNC). We have found MNC in hydrates of mono- and tetra-alkyl ammonium ions, NH3(C m H2m+1)+(H2O) n , m=1–8 and N(C m H2m+1) 4 + (H2O) n , m=2–8. In contrast, NH2(CH3) 2 + (H2O) n , NH(CH3) 3 + (H2O) n1 and N(CH3) 4 + (H2O) n do not exhibit any MNC. We conjecture that the structures of these magic number clusters correspond to exohedral structures in which the ion is situated on the surface of the water cage in contrast to the widely accepted caged ion structures of H3O+(H2O) n and NH 4 + (H2O) n .  相似文献   

2.
Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C2H4)n(CH3OH)mH+]/[(C2H4)n(CH3OH)m+], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C2H4)n(CH3OH)m+ and (C2H4)n(CH3OH)m–1CH3O+ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C2H4)n(CH3OH)mH+ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH3OH)H3O+, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C2H4)n(CH3OH)mH+(n + m ≤ 3) using semi-empirical molecular orbital calculations.  相似文献   

3.
The reaction of benzoyl ion with ammonia in multiple-collision conditions in the second quadrupole assembly of a triple quadrupole mass spectrometer at (laboratory) ion kinetic energies from 0 to 20 eV produced the even-electron ions [C6H5]+, [C6H5NH3·(NH3)m]+ (m = 0, 1) and [C6H5CONH3·(NH3)n]+ (n = 0, 1, 2, 3) and the odd-electron ions [C6H4NH3·(NH3)p]+· (p = 0, 1). Thermochemical information could not be obtained under multiple-collision conditions: both exothermic and endothermic reactions were observed, with no translational-energy onset measurable for the endothermic processes, nor decrease in the yield of the exothermic processes at high energies. The behaviour of cluster-ion intensities as pressure varied was qualitatively as expected. There are pressure and energy regions where spectra change little; if this feature were to be general, it would point to some utility for these conditions in qualitative analysis.  相似文献   

4.
Neutral clusters (NH3) n ((CH3)3N) m and (H2O) n ((CH3)3N) m , prepared in a pulsed nozzle supersonic expansion, are ionized by multiphoton ionization and investigated with a reflectron time-of-flight mass spectrometry technique. The observed mixed cluster ions display a maximum intensity atm=2(n+1) whenn ≦ 5 for (NH3) n ·((CH3)3N) m H+ andm=n+2 whenn ≦ 4 for (H2O) n ((CH3)3N) m H+ indicating that the cluster ions with these combinations have a stable closed shell structure. However, the pattern begins to break down whenn>5 for ammonia system andn>4 for water system. Thereupon, the most intense peaks are reached with one molecule less than the pattern required, i.e.m=2(n+1)?1 whenn=6 for (NH3) n ((CH3)3N) m H+ andm=(n+2)?1 whenn=5 for (H2O) n ((CH3)3N) m H+. These findings strongly suggest the onset of hydrogen-bonded ring structures from chain-like ones at critical cluster sizes. This is also supported by the studies of the metastable decomposition.  相似文献   

5.
Two-photon ionization mass spectra are obtained for NH3H2O binary clusters both with a nozzle beam and an ArF excimer laser. The detected major ions are H+(NH3)n(H2O)m(1 <m + n < 9). The results suggest that ammonia molecules constitute an inner shell which is surrounted by water molecules.  相似文献   

6.
Ternary clusters (NH3)·(H2SO4)·(H2O)n have been widely studied. However, the structures and binding energies of relatively larger cluster (n > 6) remain unclear, which hinders the study of other interesting properties. Ternary clusters of (NH3)·(H2SO4)·(H2O)n, n = 0-14, were investigated using MD simulations and quantum chemical calculations. For n = 1, a proton was transferred from H2SO4 to NH3. For n = 10, both protons of H2SO4 were transferred to NH3 and H2O, respectively. The NH4+ and HSO4 formed a contact ion-pair [NH4+-HSO4] for n = 1-6 and a solvent separated ion-pair [NH4+-H2O-HSO4] for n = 7-9. Therefore, we observed two obvious transitions from neutral to single protonation (from H2SO4 to NH3) to double protonation (from H2SO4 to NH3 and H2O) with increasing n. In general, the structures with single protonation and solvated ion-pair were higher in entropy than those with double protonation and contact ion-pair of single protonation and were thus preferred at higher temperature. As a result, the inversion between single and double protonated clusters was postponed until n = 12 according to the average binding Gibbs free energy at the normal condition. These results can serve as a good start point for studies of the other properties of these clusters and as a model for the solvation of the [H2SO4-NH3] complex in bulk water.  相似文献   

7.
Compounds C6H5X(X ? F, Cl, Br, NO2, CN, OCH3) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C6H5NH3]+ (m/z 94). [NH4]+ reacts with C6H5X(X ? F, Cl, Br) to yield m/z 94 but C6H5X (X ? CN, NO2) forms this ion only by reactions involving either [NH3]+ or [C6H5X]+. C6H5OCH3 does not form m/z 94.  相似文献   

8.
The processes of H3O+ production from alcohols (ethanol, 2‐propanol, 1‐propanol, 2‐butanol) and ethers (diethyl ether and ethyl methyl ether), and their deuterium‐substituted species, by intense laser fields (800 nm, 100 fs, ~1 × 1014 W/cm) were investigated through time‐of‐flight (TOF) mass spectrometry. H3O+ formation was observed for all these compounds except for ethyl methyl ether. From the analysis of TOF signals of H(3?n)DnO+ (n = 0, 1, 2, and 3) that have expanding tails with increasing flight time, it has been confirmed that the reaction proceeds through metastable dissociation from the intermediate species C2H(5?m)DmO+(m = 0–5). The common shape of the H(3?n)DnO+ signal profiles contains two major distributions in the time constant, i.e., fast and slow components of <50 ns and ~500 ns, respectively. The H(3?n)DnO+ branching ratio is interpreted to be the result of complete scrambling of four hydrogen atoms at the C? C site in C2H4‐OH+, and partial exchange (18–38%) of a hydrogen atom in the OH group with four other hydrogen atoms within 1 ns prior to H(3?n)DnO+ production. Ab initio calculations for the isomers and transition states of C2H5O+ were also performed, and the observed H(3?n)DnO+ production mechanism has been discussed. In addition, a stable isomer having a complex structure and two isomerization pathways were discovered to contribute to the H3O+ formation process. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
The self-assembly behaviors of a series of zwitterionic heterogemini surfactants CmH2m+1-PO4–(CH2)2-N+(CH3)2-CnH2n+1, abbreviated as Cm-P-N-Cn (m, n?=?9, 9; 9, 12; 9, 15; 9, 18; 12, 12; 12, 15; 12, 18; 15, 15; 15, 18; 18, 18), have been investigated in aqueous solution by the dissipative particle dynamics (DPD) method. Morphologies such as sphere (S), rod (R), planar grid (PG), lamella (L), honeycomb (H), one-, two-, and three-dimensional tunnels (1DT, 2DT, and 3DT) have been observed showing more diversities than those of the corresponding symmetric gemini surfactants Cm-N-N-Cm (m?=?9, 12, 15, 18). With the increase of surfactant concentration in the aqueous solution, a distinct transition path ‘‘S—R—PG—3DT—L—2DT—1DT’’ is proved to be common for all the Cm-P-N-Cn systems. Besides, the hydrophobic chain length has a significant influence on the self-assembly behaviors in the case of m?≠?n. Radial distribution function is an effective method to quantitatively evaluate the interaction and relationship between each functional group in the surfactant molecule and water. Results can provide a new insight into the self-assembly behaviors of zwitterionic heterogemini surfactants and the corresponding applications.  相似文献   

10.
Homoadamantane derivatives can be divided into two groups according to their mass spectra. To the first group belong compounds with electron attracting substituents (COOH, CI, COOCH3, Br); compounds with electron releasing substituents (OCH3, OH, NH3, NHCOCH3) constitute the second group. The most characteristic feature of the first group compounds is the splitting off of the substituent. The hydrocarbon fragment [C11H17]+ thus formed then loses olefin molecules with the formation of corresponding ionic species C11?nH17?2n. The 3-substituted compounds of this group undergo thermal Wagner-Meerwein type rearrangements into adamantane derivatives, resulting in the [C10H15]+ (m/e 135) ion formation; this is the main difference between 1- and 3-substituted homoadamantanes. The series of [CnH2n?6X]+ ions (where X = OCH3, OH, NH2, NHCOCH3, n = 6 to 10) are characteristic of the mass spectra of the second group compounds, the ion [C6H6X]+, [M ? C5H11]+ being the most abundant. The intensity ratio of [M ? C5H11]+ to [M ? C4H9]+ ions is 10:1 for 1-substituted and 3:1 for 3-substituted compounds of this group, allowing the location of the substituent. Some individual features of the spectra are also reported.  相似文献   

11.
Silicone resins can be used as polymeric precursors in the production of ceramic materials. Cohydrolysis of mixtures of trimethylchlorosilane, methyldichlorosilane, vinylmethyldichlorosilane and phenyltrichlorosilane leads to the formation of especially suitable polysiloxanes, but also low-molar mass siloxanes are formed as undesired by-products. The structures of these by-products have been elucidated. Vaporizable components of the matrix have been isolated by distillation, separated using gas chromatography and identified by mass spectrometry in EI (electron impact ionization) and CI (chemical ionization with isobutane) mode. The EI mass spectra of the siloxane oligomers with different numbers of Si-H, Si-phenyl and Si-vinyl groups show characteristic fragments like Me3Si+, ViMe2Si+, Vi2MeSi+, PhMe2Si+, and Ph2MeSi+, which give a first indication to the structure, but generally do not show molecular peaks. A reliable determination of the molar mass has been possible considering the CI-ions and CI-fragments [M+1]+, [M−1]+, [M−27]+ and [M−77]+, respectively. The compounds M2DPh,OH and M3TPh have been identified as main components of the investigated siloxane mixture. Besides, numerous linear compounds of the type M2(DH)n(DVi)m and M2TPh(DH)n(DVi)m M as well as cyclic ones of the structure [MTPh(DH)n(DVi)m] with n, m=0–3 have been indicated. Received: 3 March 1995/Revised: 25 March 1995/Accepted: 3 April 1995  相似文献   

12.
Solubility in ternary aqueous stratifying systems containing Catamine AB (alkylbenzyldimethylammonium chloride [C n H2n + 1N+(CH3)2CH2C6H5] · Cl, a cationic surfactant, where n = 10–18) and LiCl, NaCl, KCl, and NH4Cl inorganic salts was studied for the first time at 25°C. The boundaries of two-phase liquid equilibrium fields were determined. The studied stratifying systems were proposed for use in the liquid extraction of metal ions.  相似文献   

13.
By checking the chemistry underlying the concept of “supramolecular cluster catalysis” we identified two major errors in our publications related to this topic, which are essentially due to contamination problems. (1) The conversion of the “closed” cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ (1) into the “open” cluster cation [H2Ru3(C6H6)(C6Me6)2(O)(OH)]+ (2), which we had ascribed to a reaction with water in the presence of ethylbenzene is simply an oxidation reaction which occurs in the presence of air. (2) The higher catalytic activity observed with ethylbenzene, which we had erroneously attributed to the “open” cluster cation [H2Ru3(C6H6)(C6Me6)2(O)(OH)]+ (2), was due to the formation of RuO2 · nH2O, caused by a hydroperoxide contamination present in ethylbenzene.  相似文献   

14.
Reactions of gold anions and cations generated by laser desorption/ionization were studied in the FTICR spectrometer. Au associated with C6F6 to give the novel Au(C6F6) complex, whose binding energy was estimated to be 24 ± 4 kcal mol−1 from analysis of the radiative association (RA) kinetics. Au+ associated with C6F5H to give Au+(C6F5H), with binding energy estimated to be 31 kcal mol−1. Au+ reacted with C6H6 to form the well known Au+(C6H6) and Au+(C6H6)2 complexes. The observation of rapid charge transfer from Au+(C6H6) to C6H6 was interpreted as showing that benzene binds more strongly to neutral Au than to Au+. The neutral Au–C6H6 bond is accordingly concluded to be stronger than about 70 kcal mol−1.  相似文献   

15.
The results on the synthesis and study of the crystal structures of compounds based on anionic fragments {VO(Cbdc)2}2– formed by oxovanadium(IV) (vanadyl, VO2+) and two chelate-bound anions of cyclobutane-1,1-dicarboxylic acid (H2Cbdc = C4H6(COOH)2) are presented. The use of ammonium cation NH4+ as a counterion in the synthesis leads to the formation of the mononuclear complex (NH4)2[VO(Сbdc)2(H2O)] · 2H2O (I). In the case of K+ cation, compound [K4(VO)2(Сbdc)4(H2O)4] n (II) with the 3D polymeric crystal structure is formed. The reaction of compound II with Mg(NO3)2 · 6H2O in an aqueous solution involves the partial substitution of K+ by Mg2+ cations to form 1D polymeric compound {[KMg0.5(VO)(Сbdc)2(H2O)6.5] · 3H2O} n (III), while a similar reaction of compound I does not afford the product of substitution of NH4+ by Mg2+ cations (CIF files CCDC 1551021–1551023 for compounds IIII, respectively).  相似文献   

16.
The 70 eV electron ionization mass spectra of polycyclic aromatic compounds are characterized by the presence of relatively stable multiply charged molecular ions [M]n+ (n=2–4). When generated from the compounds benzene, napthalene, anthracene, phenanthrene, 2,3-benzanthracene, 1,2-benzanthracene, chrysene, 9,10-benzophenanthrene and pyrene, the relative abundances of the multiply charged ions increase dramatically with the number of rings. These compounds form multiply charged molecular ions (n=2, 3) which undergo unimolecular decompositions indicative of considerable ionic rearrangement. The main charge separation processes observed here [M]2+→m1++m2+, [M]3+˙→m3++m→+m42+) involve, in almost every case, one or more of the products [CH3]+, [C2H3]+˙ and [C3H3]+. This suggests the existence of preferred structures amongst the metastable parent ions. Information on the relative importance of the various fragmentation pathways is presented here along with translational energy release data. Some tentative structural information about the metastable ions has been inferred from the translational energy release on the assumption that the released energy is due primarily to coulombic repulsion within the transition state structure. For the triply charged ions these interpretations have necessitated the use of a coulombic repulsion model which takes account of an extra charge. Vertical ionization energies for the process [M]n++G→[M](n+1)+G+e? (charge stripping) have also been determined where possible for n=1 and 2 and the results from these experiments allow the derivation of simple empirical equations which relate successive ionization energies for the formation of [M]2+ and [M]3+˙ to the appearance energy of [M]+˙.  相似文献   

17.
Five novel phosphate-type hybrid surfactants, CmF2m+1C6H4CH[OPO2(OC6H5)Na]CnH2n+1 (FmPHnPPhNa: m = 4, 6, 8; n = 3, 5), have been synthesized. When compared with sulfate-type hybrid surfactants, CmF2m+1C6H4CH(OSO3Na)CnH2n+1 (C6H4 = p-phenylene), the new hybrid surfactants were found to have comparable abilities to lower the surface tension of water. The critical micelle concentrations of FmPHnPPhNa followed Klevens’ rule and their occupied areas per molecule increased with increasing m and n. Calcium hydroxyapatite (CaHAp) pellets modified with FmPH3PPhNa gave high hydro and lipophobic surfaces. The hybrid surfactants are expected to be useful as new dental reagents for oral hygiene.  相似文献   

18.
For compounds C6H5X (X?Cl, Br, I) under chemical ionization conditions, methylamine causes ipso substitution of X by [NH2CH3]+ and by [NH2]+˙. C6H5F is less reactive; it gives some [C6H5NH2]+˙. Nitrobenzene gives an adduct ion [M+CH3NH3]+, a reduction product ion [C6H5NO2]+˙, and an ion at m/z93, probably a substitution product [C6H5NH2]+˙, but no [C6H5NH2CH3]+. It is also shown that the ion m/z94, formed from nitrobenzene with ammonia as reagent gas, is a substitution product rather than a reduction product ion. Carbonyl compounds C6H5. CO. X give adduct ions and some substitution, mainly [C6H5NH2]+˙.  相似文献   

19.
The yields of tris(2,4-pentanedionato)chrvmium(III) (Cr(acac)3) formed in the presence of either the ammonia (Am), ethanoate (ET), trichloroethanoate (TCE), or trifluoroethanoate (TFE) ligand in high pH aqueous solution, were compared with those from a medium containing only hydroxyl and water as the principal ligands besides the acac. The presence of Am, ET, and TCE drastically reduced the yields at pH’s 9.5–10.5, 7.5–9.0/9.5–11.0, and 9.0–12.0, respectively in increasing order ET > Am < TCE. The role of Am is attributed mainly to the oxo-bridged species ((OH)m(H2O)nAm5-(m+n)Cr(O)(OH)CrAm5-(m+n)(H2O)n(OH)m)3-2m (1), ((OH)m(H2O)nAm5-(m+n)Cr(O)2CrAm5-(m+n)(H2O)n(OH)m)2-2m (2), and ((OH)m(H2O)nAm5-(m+n)Cr(O)(OH)CrAm4(m+n)(H2O)n(OH)m+1)2-2m (3). 2 is the most deactivating species mainly on the basis that the Cr-O bond of the oxo-bridge is suggested as being stronger than the Cr-O bond of the hydroxo-bridge. As for ET and TCE, oxo-bridged polymeric ethanoato- and trichloroethanoatochromium(III) species are also proposed as the main origin of the drastic deactivation of the reaction not observed for TFE due possibly, to the insignificance of oxo-bridges in tnfluoroethanoatochromium(III) species.  相似文献   

20.
Structures and energetic characteristics of Li(H2O) n and Li+(H2O) n clusters with n = 1–6, 19, and 27 determined in the second order of the Møller-Plesset perturbation theory with 6–31++G(d,p) basis set are analyzed. The electron density redistribution, which takes place upon the electron addition to a Li+(H2O) n cluster, is found to be provided by hydrogen-bonded water molecules: initially almost neutral molecules, which are most distant from lithium, become negatively charged. The calculated energies of the electron capture by Li+(H2O) n clusters are approximated with the appropriate electrostatic model, and estimates of the lithium ionization energy in water clusters of various sizes are found. Similar estimates obtained earlier for sodium are made more accurate.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号