NH3R++NHR2(R=H,CH3)体系质子传递反应的从头算研究

用从头计算法在HF/6-31G^*基组水平上研究了NH₄⁺+NH₃→NH₃+NH₄⁺,NH₄⁺+NH₂CH₃→NH₃+NH₃CH₃⁺,NH₄⁺+NH(CH₃)₂→NH₃+NH₂(CH₃)₂⁺以及NH₃CH₃⁺+NH₂CH₃→NH₂CH₃+NH₃CH₃⁺等4个体系的质子传递反应的机理.结果表明:(1)上述质子传递反应均具有双阱型的势能面,质子沿N(1)、N(2)连线直接传递;(2)质子受体分子中的甲基对质子传递起促进作用,而质子给体离子中的甲基则阻碍质子的传递。     

N2O+离子B2П态的光谱与光解离动力学

用一束波长为360.55 nm的激光直接作用于超声射流的N₂O分子束, 通过(3+1)共振增强多光子电离(REMPI)过程制备纯净的N₂O⁺(X²П(0,0,0))母体离子, 再用另一束波长在243-278 nm范围的激光将母体离子激发至B²П态后解离. 扫描解离激光波长, 监测NO⁺离子碎片的强度, 从而获得N₂O⁺离子B²П态的光致碎片激发(PHOFEX)谱. 通过拟合转动分辨光谱, 得到了相应的转动常数和自旋分裂常数, 从而区分了A²Σ⁺态高振动能级和B²П态带源的贡献, 明确了N₂O⁺离子B²П态的光谱"带头"位置(37154 cm^-1), 并将获得的振动光谱初步归属为B²П(v₁,v₂,v₃)←X²П的振动跃迁序列. 通过对NO⁺碎片离子的飞行时间质谱峰形的分析, 还获得了解离过程中释放的平均平动能, 并结合电子激发态势能面, 讨论了N₂O⁺离子B²П态的解离机理.     

离子色谱法同时测定饮水中9种阴离子

建立离子色谱抑制电导检测法同时测定饮水中F^-、Cl O₂^-、Cl^-、NO₂^-、Cl O₃^-、Br^-、NO₃^-、H₂PO₄^-和SO₄^2-9种阴离子的方法。采用SH-AP-2型阴离子交换柱为分离柱，以4.0 mmol/L Na₂CO₃-4.0 mmol/L Na HCO₃溶液为淋洗液，流量为0.80 m L/min，采用等度洗脱方式将9种阴离子完全分离，利用抑制电导检测。Cl O₂^-、Cl O₃^-的质量浓度在0.05～2.0 mg/L范围内，SO₄^2-     

拉曼光谱法研究Na+, Mg2+//SO42-, Cl-, H2O四元体系中SO42-离子缔合结构特征及其变化规律

复杂水盐体系存在稳态和介稳固液相平衡以及复杂的成盐规律。为了解固液平衡状态下液相的结构特征,本文采用拉曼光谱技术并结合高斯-洛伦兹去卷积分峰拟合程序对Na⁺, Mg²⁺//SO₄^2-, Cl^-, H₂O四元体系及其二元和三元子体系中ν₁-SO₄^2-的离子缔合结构特征进行了分析。研究结果表明:SO₄^2-在Na₂SO₄-H₂O体系存在自由态SO₄^2-和SO₄^2-离子簇两种结构,在MgSO₄-H₂O, MgSO₄-MgCl₂-H₂O及Na⁺, Mg²⁺//SO₄^2-, Cl^-, H₂O等含镁体系中,还有Mg²⁺-H₂O-SO₄^2-和Mg²⁺-OSO₃^2-两种缔合结构。在二元和三元体系中ν₁-SO₄^2-的离子缔合结构以自由态SO₄^2-为主,随着SO₄^2-离子总浓度的变化,上述四种结构所占比例会发生规律性变化。Na⁺, Mg²⁺//SO₄^2-, Cl^-, H₂O四元体系在NaCl减少及等温蒸发过程中,自由态SO₄^2-结构比例逐步降低, Mg²⁺和SO₄^2-相结合形成Mg²⁺-H₂O-SO₄^2-或Mg²⁺-OSO₃^2-结构的机会增多,在复盐区还会形成SO₄^2-离子簇结构。由此判断溶液结构的适应性变化是导致介稳现象的重要原因。进一步的相关分析表明:SO₄^2-的浓度和耶涅克指数J与ν₁-SO₄^2-峰的峰强度和峰面积存在正相关关系, Mg²⁺浓度是影响ν₁-SO₄^2-峰中四种缔合结构的比例发生变化的主要因素。     

风化壳淋积型稀土矿多级逆流浸取实验研究

风化壳淋积型稀土矿的开采主要通过浸矿剂离子与吸附在黏土矿物表面的稀土离子发生离子交换浸出反应实现。以(NH₄)₂SO₄为浸矿剂,采用多级逆流浸取的方式研究了风化壳淋积型稀土矿的浸矿过程,通过在逐级浸取过程中浸出液组分的变化分析了矿土中稀土离子(RE³⁺)和主要杂质铝离子(Al³⁺)的浸出行为,并基于浸矿剂的消耗规律探讨了浸矿剂离子与RE³⁺和Al³⁺的离子交换反应机制以及原矿土的净吸附量。结果表明,在浸矿液逐级浸取新鲜矿土的过程中,浸出液中的RE³⁺和Al³⁺浓度逐渐增加,铵根离子(NH₄⁺)逐渐消耗,交换进入浸出液中的RE³⁺和Al³⁺逐级减少;同时,浸出液中的硫酸根离子(SO₄^2-)逐级损耗,说明新鲜矿土除因发生离子交换反应消耗NH₄<...     

生物铵转运蛋白对NH3/NH4+作用机理研究

铵转运蛋白广泛存在于细菌、真菌、植物以及动物等各种生命体中。生物铵转运蛋白对NH₃/NH₄⁺的传输作用已被广泛研究,然而,对于通过铵转运蛋白疏水性孔腔的物种是带电荷的NH₄⁺离子还是电中性的NH₃分子,仍存在很大争议。本文综述了近年来生物铵转运蛋白对NH₃/NH₄⁺作用机理的研究进展,主要包括NH₃或NH₄⁺的传输及NH₃和H⁺共传输等机理。     

基态H2O+的全域多体势能面

基态H₂O⁺分子离子是重要的星际反应中间体.用MRCISD/cc-pVTZ先计算H₂O⁺势能面,然后拟合成多体势能函数.全域势能面能很好地描述基态H₂O⁺的行为.与两条反应通道的实验能变和其构型翻转反应能垒比较,表明计算结果与实验值相符.对计算点完成了力场的多项式拟合,对其振动模式进行了分析     

Ag和Pd及其离子对TiO2光催化分解CH3CHO的影响

当用能量大于其禁带宽度的光照射通有氧气的TiO₂悬浮液时,在TiO₂微粒表面会产生反应活性很高的空穴和O₂^-、H₂O₂等多种活性氧.在上一篇文章中^[1]我们已报道了在通氧气和紫外光照的条件下,向TiO₂悬浮液中加入少量Ag⁺或Pd²⁺,将会大幅度提高体系中H₂O₂的生成量.另外,蔡汝雄等人也曾通过向TiO₂悬浮液中加入SOD的方法来提高其中H₂O₂的生成量^[2],而且证明了H₂O₂生成量的增多有助于杀死子宫癌细胞^[3].另一方面,利用TiO₂光催化来分解处理工业废水中的有机物已多见报道^[4～7].因此,为考察H₂O₂含量的增加是否有助于TiO₂催化分解有机物,我们以CH₃CHO为氧化对象,测定了经Ag和Pd表面修饰以及直接向悬浮体系添加Ag⁺或Pd²⁺离子前后,TiO₂光催化氧化分解CH₃CHO效率的变化,并对氮气和氧气气氛的实验结果进行了测定和比较.     

激光烧蚀Al+与乙醇团簇的反应研究

利用激光烧蚀-分子束法对Al等离子体与乙醇团簇的反应进行了研究.飞行时间质谱测得的主要反应产物有Al⁺(C₂H₅OH)_n (n=3～10)与H⁺(C₂H₅OH)_n (n=1～14)团簇正离子和(C₂H₅OH)_n(H₂O)OH^- (n=0～8)团簇负离子.实验发现,烧蚀产生的Al等离子体与脉冲分子束的不同位置反应,对团簇离子的类别、大小及强度分布均产生很大影响.Al等离子体与脉冲分子束的前段反应,主要产生金属-复合物团簇离子Al⁺(C₂H₅OH)_n,且信号较强;Al等离子体与脉冲分子束的中段及后段反应,主要产生质子化团簇离子H⁺(C₂H₅OH)_n和团簇负离子(C₂H₅OH)_n(H₂O)OH^-,同时还出现强度较小的其他水合团簇离子,如H⁺(H₂O)m(C₂H₅OH)_n (m=1～2)等.     

乙二胺杂化锗酸锌纳米带的绿色合成及其对铀酰离子的吸附与检测

该文采用水热法合成了一种新型乙二胺杂化的锗酸锌纳米带(NH₂-Zn₂GeO₄ NRs),并用于铀酰离子(UO₂²⁺)的检测和吸附。利用透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)、X射线衍射(XRD)、紫外-可见吸收光谱(UV-Vis)以及荧光光谱等对纳米带的结构及其光学特性进行了表征。结果表明NH₂-Zn₂GeO₄ NRs表面含有大量的—Ge—O—H和—NH₂基团,为UO₂²⁺的检测和吸附提供了丰富的结合位点。此外NH₂-Zn₂GeO₄ NRs可高效、高选择性地吸附和检测UO₂²⁺,其对UO₂²⁺的吸附符合Langmuir等温模型,最大吸附量为190 mg...     

Differentiation of isobaric compounds using chemical ionization reaction mass spectrometry

The technique of proton transfer reaction mass spectrometry (PTR-MS) couples a proton transfer reagent, usually H3O+, with a drift tube and mass spectrometer to determine concentrations of volatile organic compounds. Here we describe a first attempt to use chemical ionization (CI) reagents other than proton transfer species inside a PTR-MS instrument. The ability to switch to other types of CI reagents provides an extra dimension to the technique. This capability is demonstrated by focusing on the ability to distinguish several isobaric aldehydes and ketones, including the atmospherically important molecules methacrolein and methyl vinyl ketone. Two CI reagents were selected, H3O+ and NO+, both being cleanly generated in a low intensity radioactive source prior to injection into the drift tube. By recording spectra with both of these reagents, the contributions from different isobaric molecules can be separated by virtue of their unique spectrometric 'fingerprints'. The work demonstrates that this form of instrumentation is not restricted to proton transfer reagents and is the basis of a more general technique, chemical ionization reaction mass spectrometry (CIRMS).     

Differentiation of isomeric compounds by two-stage proton transfer reaction time-of-flight mass spectrometry

We investigated a two-stage ion source for proton transfer reaction (PTR) ionization to achieve more selective mass spectrometric (MS) detection of selected volatile organic compounds (VOCs) than that achieved with commonly used PTR-MS instruments, which are based on single-step PTR ionization with H3O+. The two-stage PTR ion source generated reagent ions other than H3O+ by an initial PTR between H3O+ and a selected VOC, and then a second PTR ionization occurred only for VOCs with proton affinities larger than the affinity of the reagent VOC. Acetone and acetonitrile were useful as reagent VOCs because they provided dominant peaks as a protonated form. Using two-stage PTR-MS, we differentiated isomeric VOCs (for example, ethyl acetate and 1,4-dioxane) by means of differences in their proton affinities; protonated acetone formed the [M + H]+ ion from ethyl acetate but not from 1,4-dioxane. The PTR-MS-derived concentrations agreed quantitatively with those independently determined by Fourier transform infrared spectroscopy (FT-IR) at parts per million by volume (ppmv) levels. In addition, interfering fragment ions formed from alkyl benzenes at m/z 79 (C6H7+) could be distinguished from the m/z 79 ion arising from protonation of benzene, and therefore this method would prevent overestimation of benzene concentrations in air samples in which both benzene and alkyl benzenes are present. This two-stage PTR ionization may be useful for distinguishing various isomeric species, including aldehydes and ketones, if appropriate reagent ions are selected.     

质子转移反应质谱用于痕量挥发性有机化合物的在线分析

质子转移反应质谱(PTR-MS)是一种化学电离源质谱技术,专门用于痕量挥发性有机化合物(VOCs)实时在线检测.此技术利用H3O-作化学电离源试剂离子与作为质子接受体的VOCs发生质子转移反应.大气中的O2,N1,CO2等主要成分由于其质子亲和势低于H2O,而不与H3O发生质子转移反应,因此可在大气环境下检测痕量VOC...     

希土离子单硫代二苯甲酰甲烷配合物的合成及性质研究

本文合成了单硫代二苯甲酰甲烷(HTDBM)和三价希土离子及路易斯碱(Q)的Ln(TDBM)_4QH型配合物(Ln=除Ce外的La～Lu,Q=二乙基胺)。测定了它们的摩尔电导值、红外光谱,可见—紫外光谱,核磁共振谱.观察到配合物是通过硫原子、氧原子同时与Ln~(3+)离子配位.Ln-O键强于Ln-S键。在Nd~(3+)、Pr~(3+)、Ho~(3+)、Er~(3+)离子的该类配合物的可见吸收光谱中发现超灵敏跃迁现象。讨论了题述配合物作为核磁共振化学位移试剂的可能性.     

潮湿空气微波放电离子形成动力学

利用微波放电电离质谱装置，通过水蒸气与空气混合气体（潮湿空气）的微波放电，同时获得了化学电离质谱探测技术中常用的三种重要母体离子H3O＋、NO＋和.结合潮湿空气中主要成分N2、O2以及水蒸气各自微波放电后的质谱探测结果，对潮湿空气微波放电后上述三种离子产生的动力学过程进行了分析，并给出了各种离子的形成机制.这些离子 分子反应过程在计算机模拟中得到了进一步的证实.     

An investigation of the reactions of H3O+ and O2+ with NO, NO2, N2O and HNO2 in support of selected ion flow tube mass spectrometry

A selected ion flow tube (SIFT) experimental investigation has been carried out of the reactions of H3O+, NO+ and O2+ with NO, NO2, N2O and HNO2, in order to obtain the essential kinetic data for the analyses of these compounds in air using selected ion flow tube mass spectrometry (SIFT-MS). These investigations show that NO+ ions do not react at a significant rate with any of these NOx compounds and that H3O+ ions react only with HNO2 (product ions H2NO2+ (75%) and NO+ (25%)). O2+ ions react with NO (product ion NO+), NO2 (product ion NO2+) and HNO2 (product ions NO+ (75%), NO2+ (25%)), but not with N2O. We conclude that both NO and NO2 can be accurately quantified in air using only O2+ precursor ions and SIFT-MS when HNO2 is not present. However, when HNO2 is present it invariably co-exists with both NO and NO2 and then both H3O+ and O2+ precursor ions are needed to determine the partial pressures of NO, NO2 and HNO2 in the air mixture. We also conclude that currently N2O cannot be analysed in air using SIFT-MS.     

An online ultra-high sensitivity Proton-transfer-reaction mass-spectrometer combined with switchable reagent ion capability (PTR + SRI − MS)

Proton-transfer-reaction mass-spectrometry (PTR-MS) developed in the 1990s is used today in a wide range of scientific and technical fields. PTR-MS allows for real-time, online determination of absolute concentrations of volatile (organic) compounds (VOCs) in air with high sensitivity (into the low pptv range) and a fast response time (in the 40–100 ms time regime). Most PTR-MS instruments employed so far use an ion source consisting of a hollow cathode (HC) discharge in water vapour which provides an intense source of proton donor H₃O⁺ ions. As the use of other ions, e.g. NO⁺ and O₂⁺, can be useful for the identification of VOCs and for the detection of VOCs with proton affinities (PA) below that of H₂O, selected ion flow tube mass spectrometry (SIFT-MS) with mass selected ions has been applied in these instances. SIFT-MS suffers, however, from at least two orders lower reagent ion counts rates and therefore SIFT-MS suffers from lower sensitivity than PTR-MS.Here we report the development of a PTR-MS instrument using a modified HC ion source and drift tube design, which allows for the easy and fast switching between H₃O⁺, NO⁺ and O₂⁺ ions produced in high purity and in large quantities in this source. This instrument is capable of measuring low concentrations (with detection limits approaching the ppqv regime) of VOCs using any of the three reagent ions investigated in this study. Therefore this instrument combines the advantages of the PTR-MS technology (the superior sensitivity) with those of SIFT-MS (detection of VOCs with PAs smaller than that of the water molecule and the capability to distinguish between isomeric compounds).We will first discuss the setup of this new PTR+SRI-MS mass spectrometer instrument, its performance for aromates, aldehydes and ketones (with a sensitivity of up to nearly 1000 cps/ppbv and a detection limit of about several 100 ppqv) and finally give some examples concerning the ability to distinguish structural isomeric compounds.     

Gas-phase reactions and rearrangements of alkyl esters with H3O+, NO+, and O2*+: a selected ion flow tube study

Selected ion flow tube mass spectrometry (SIFT-MS) has been employed to study the ion-molecule reactions of 17 alkyl esters reacting with the common SIFT-MS reagent ions, H3O+, H3O+.nH2O (n = 1, 2, 3), NO+, and O2+. The majority of reactions were observed to proceed at or near collision rate, with the exception of H3O+.3H2O, which was found to be slow for 8 of 17 alkyl esters. Unexpected product ions in the form of the parent carboxylic acid cation were observed to arise from the H3O+ and NO+ reactions of some alkyl esters. The observed reactions have been probed by the ab initio CBS-4M and G2(MP2,SVP) methods. The postulated reaction pathway involves a 1,5 H atom migration from a beta-carbon onto the carbonyl oxygen.     

Simultaneous uptake of Ni2+, NH4+ and PO4(3-) by amorphous CaO-Al2O3-SiO2 compounds

Simultaneous uptake of Ni2+, NH4+, and PO4(3-) by amorphous CaO-Al2O3-SiO2 (C-A-S) compounds was investigated using batch and column methods. Fifteen different C-A-S samples with systematically varied chemical compositions were prepared by coprecipitation from ethanol-water solutions containing Ca(NO3)2.4H2O, Al(NO3)3.9H2O, and Si(OC2H5)4, using NH4OH as the precipitating agent. The resulting precipitates were dried and heated at various temperatures to produce the C-A-S samples, which were then characterized by XRD, FTIR, solid state MAS NMR, DTA-TG, and N2 adsorption. All the C-A-S samples prepared at 600-900 degrees C were amorphous, apart from the CaO-rich samples. Simultaneous uptake of Ni2+, NH4+, and PO4(3-) was determined by a batch method using a solution with an initial concentration of 2 mM. In these experiments, the uptake abilities of the C-A-S samples for Ni2+ and PO4(3-) were high, but were relatively low for NH4+. The uptake abilities for Ni2+ and PO4(3-) increased but that for NH4+ decreased as the silica content in the C-A-S decreased, suggesting that similar uptake mechanisms (ion substitution and/or precipitation) are operating for Ni2+ and PO4(3-), but the uptake mechanism for NH4+ is different (physical adsorption). The column experiments indicate that the order of uptake ability of C-A-S for the three ions is NH4+ < PO4(3-) < Ni2+. Although the silica content of the C-A-S does not have the expected influence on the uptake of these three ions, for NH4+ it plays an important role in the formation of the amorphous phase and also in the suppression of Ca2+ and/or Al3+ release from the C-A-S during the uptake experiments. The optimum uptake properties of the C-A-S can thus be controlled by adjusting the chemical compositions and heating conditions under which the samples are prepared.     

On-line analysis of diesel engine exhaust gases by selected ion flow tube mass spectrometry

Selected ion flow tube mass spectrometry (SIFT-MS) has been used to analyse on-line and in real time the exhaust gas emissions from a Caterpillar 3304 diesel engine under different conditions of load (idle and 50% of rated load) and speed (910, 1500 and 2200 rpm) using three types of fuel: an ultra-low-sulphur diesel, a rapeseed methyl ester and gas oil. SIFT-MS analyses of the alkanes, alkenes and aromatic hydrocarbons in the headspace of these fuels were also performed, but the headspace of the rapeseed methyl ester consists mainly of methanol and a compound with the molecular formula C4H8O. The exhaust gases were analysed for NO and NO2 using O2+* reagent ions and for HNO2 using H3O+ reagent ions. The following aldehydes and ketones in the exhaust gases were quantified by using the combination of H3O+ and NO+ reagent ions: formaldehyde, acetaldehyde, propenal, propanal, acetone, butanal, pentanal, butanone and pentanone. Formaldehyde, acetaldehyde and pentenal, all known respiratory irritants associated with sensitisation to asthma of workers exposed to diesel exhaust, are variously present within the range 100-2000 ppb. Hydrocarbons in the exhaust gases accessible to SIFT-MS analyses were also quantified as total concentrations of the various isomers of C3H4, C3H6, C4H6, C5H8, C5H10, C6H8, C6H10, C7H14, C6H6, C7H8, C8H10 and C9H12.