五氧化二氮(N2O5)非均相摄取系数的定量和参数化

颗粒物污染是我国超大城市地区面临的主要污染问题,大气化学受到非均相反应的强烈影响。N₂O₅非均相反应过程的定量描述对厘清我国超大城市地区夜间大气氧化性、区域NO_x收支、臭氧生成等问题具有重要意义。本文从反应机理、摄取系数测量技术和不同气溶胶基体测量结果等方面系统总结了N₂O₅非均相反应动力学研究进展。N₂O₅非均相摄取是典型的反应性摄取过程,是气溶胶流动管测量系统的理想应用对象。实验室动力学研究从硫酸盐等模型颗粒物出发,结合外场观测获取的颗粒物信息,模拟使用的颗粒物越来越接近实际大气条件。N₂O₅在不同颗粒物表面摄取系数在0.001~0.2之间,其变化范围超过两个数量级,主要受到环境温度、湿度、颗粒物组分中NO₃^-、Cl^-、SO₄^2-、含水量、有机物、颗粒物混合状态和相态等因素影响;颗粒物中H₂O、Cl^-、SO₄^2-的浓度升高会提高非均相摄取速率,而NO₃^-、有机物则会对摄取过程产生抑制作用。欧美地区外场观测研究表明这些影响因素并不是线性叠加的,而是存在非常复杂的相互作用,基于实验室测量结果开发的参数化公式不能很好地拟合观测结果。由于N₂O₅和颗粒物的高值区共存于污染城市地区,下一步研究需要在包括我国超大城市地区在内的典型城市大气条件下开展更多的外场实测研究和建立更准确的参数化公式。     

对流层中的OH与HO2自由基的研究进展

OH与HO2自由基是大气中重要的氧化剂,研究它们的化学反应性质及对其进行实地测量,对深入理解大气氧化过程和了解区域乃至全球大气自净能力有重要意义.自工业革命以来,每年有数千万吨的自然和人为污染物进入对流层,这些物质会严重影响·OH的生成和消除,因此·OH的浓度可能在全球范围内发生大的变化.本文总结了国内外近年来有关·OH与HO2·的最新研究成果,目前比较一致的结论是由于人类活动的影响,全球·OH的浓度比工业革命前降低了.但是在一些污染地区,由于氮氧化合物对·OH的负反馈作用,一定程度上弥补了·OH的净损失.在最近20年中,·OH在对流层中的浓度基本稳定在106cm-3.本文还介绍了实验室研究方法及外场测量技术的进展,提出了尚待解决的一些问题.     

C2H与HO2双自由基反应的密度泛函理论研究

应用量子化学从头算和密度泛函理论(DFT)对C₂H与HO₂双自由基的单重态反应进行了研究.在UB3LYP/6-311G水平上优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型.在CCSD(T)/6-311G^{**水平上计算了各物种的单点能,并对总能量进行了零点能校正.研究结果表明,反应物中自由基C₂H的边端C进攻自由基HO₂的边端O是主要的进攻方式.首先形成了中间体1(HCCOOH),由此经过不同的反应通道可以得到主要产物P1,次要产物P2,P3和P5.生成P1的反应热为-814.40kJ/mol.自由基C₂H的中间C进攻自由基HO₂的边端O是次要的进攻方式,可以得到产物P4和P6.根据势能面分析,所有反应均是放热反应.}     

HO3、HO+3、HO-3光谱和结构的MP2和DFT理论研究

用B3LYP和MP2量子化学理论,详细地计算了HO3、HO+3、HO-3可能的平衡构型、能量和光谱参数,分析了它们可能的解离通道和稳定性.还分析了HO3的电离势(IE)及电子亲和势(Ea),讨论了HO3、HO3-自由基的光电子能谱的特征,及用光电子能谱去探测HO3的可能性.     

硝酸盐对羰基硫与气溶胶表面非均相反应的影响

利用原位漫反射傅里叶红外光谱(DRIFTS)对硝酸盐与α-Fe2O3形成的混合气溶胶与羰基硫(COS)的非均相反应进行研究,并比较了不同硝酸盐(NaNO3、KNO3和NH4NO3)和α-Fe2O3的混合物与COS反应的情况.结果表明:NaNO3质量分数为4％的混合颗粒物与COS反应具有最高的反应活性,相比纯α-Fe2O3的反应速率提高了约5倍;含等质量分数(24％)硝酸盐的混合物和纯α-Fe2O3对COS的转化能力依次为:α-Fe2O3/KNO3＞α-Fe2O3/NaNO3＞α-Fe2O3/NH4NO3＞α-Fe2O3,而纯NaNO3、KNO3和NH4NO3颗粒与COS不发生反应.说明硝酸盐的存在很大程度上提高了COS在α-Fe2O3颗粒物表面的转化能力.     

NH3与Cl2在y-Al2O3颗粒物表面的非均相反应

使用离子色谱分析了常温、常压、湿润和氧气存在条件下,NH₃和Cl₂在γ-Al₂O₃颗粒物表面非均相反应的产物及其受NH₃浓度、反应时间等的影响;并定量分析了NH₃、Cl₂、SO₂和NO₂单独及共存条件下,γ-Al₂O₃表面Cl^-、NO₃^-和SO₄^2-等二次无机颗粒物的生成总量.结果表明：NH₃和Cl₂在γ-Al₂O₃表面具有协同作用,2 h后Cl^-的生成总量可达589.65 μg,其生成量随时间延长而不断增加.表面氯化物的生成量在NH₃浓度为400 ppm时达到峰值,且随NH₃浓度的增加呈先增加而后减少的趋势.活性氯存在下,NH₃对颗粒物表面Cl^-、NO₃^-和SO₄^2-的生成有促进作用,且四种气体共存时复合正反馈效应最明显.同时,本研究对NH₃和Cl₂在颗粒物表面的非均相反应机理及活性氯和氨的排放对大气中二次无机颗粒物的贡献进行了探讨.     

SO_2在TiO_2颗粒物表面的非均相反应

使用漫反射红外傅里叶变换光谱(DRIFTS)原位反应器研究了SO2在TiO2颗粒物表面的非均相反应.研究了氧气浓度、相对湿度(RH)及紫外光光照对反应的影响.结果表明,SO2在TiO2颗粒物上可转化为亚硫酸盐或被氧化为硫酸盐.水汽或者紫外光照可促进SO2在TiO2颗粒物表面的非均相氧化反应,在两者都存在的情况下,对促进硫酸盐的生成有协同效应.在干态无光照条件下和一定湿度(RH=40%)紫外光照条件下,以硫酸盐的生成来计算,SO2在TiO2颗粒物表面的反应级数分别为二级和一级;反应摄取系数γBET分别为1.94×10-6和1.35×10-5.TiO2颗粒物表面的羟基参与了反应,在紫外光照下表面生成的活性氧物种在反应中起重要作用.     

甲烷与HO2反应的微观动力学研究

应用从头算方法和变分过渡态理论,在B3LYP/6-311+G^**方法下和300～2000K温度范围内研究甲烷与HO₂反应的微观动力学特性,得到由过渡态向反应物方向、向产物方向的能垒分别是11.83和102.90kJ/mol,理论计算正向反应速率常数与实验值之比为1.08～2.85,用此方法还可以预测没有实验数据的温度点反应的速率常数.     

大气颗粒物表面的非均相反应

<正>全球空气污染及气候变化的研究中,大气化学一直发挥着核心作用.大气化学研究的三个支柱方法包括实验室研究、外场观测和数值模拟.在过去半个多世纪,大量、系统的大气化学反应动力学实验室研究从分子水平     

NO2在NaCl表面的非均相反应

采用新的样品制备方法和气-固自由扩散的实验方式,使用漫反射傅立叶转换红外光谱原位反应器,结合离子色谱、X-射线光电子能谱、扫描电子显微镜等分析方法,研究了NO2在NaCl表面的非均相反应.研究表明反应不只是发生在颗粒物表面,体相也参与了反应; 颗粒物表面的活性点对反应起决定作用,同时测定了反应级数为二级,反应摄取系数为(1.54±0.70)×10-5.     

Experimental determination of the rate constants of the reactions of HO2 + DO2 and DO2 + DO2

The rate constants of the reactions of DO₂ + HO₂ (R1) and DO₂ + DO₂ (R2) have been determined by the simultaneous, selective, and quantitative measurement of HO₂ and DO₂ by continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near infrared, coupled to a radical generation by laser photolysis. HO₂ was generated by photolyzing Cl₂ in the presence of CH₃OH and O₂. Low concentrations of DO₂ were generated simultaneously by adding low concentrations of D₂O to the reaction mixture, leading through isotopic exchange on tubing and reactor walls to formation of low concentrations of CH₃OD and thus formation of DO₂. Excess DO₂ was generated by photolyzing Cl₂ in the presence of CD₃OD and O₂, small concentrations of HO₂ were always generated simultaneously by isotopic exchange between CD₃OD and residual H₂O. The rate constant k₁ at 295 K was found to be pressure independent in the range 25–200 Torr helium, but increased with increasing D₂O concentration k₁ = (1.67 ± 0.03) × 10⁻¹² × (1 + (8.2 ± 1.6) × 10⁻¹⁸ cm³ × [D₂O] cm⁻³) cm³ s⁻¹. The rate constant for the DO₂ self-reaction k₂ has been measured under excess DO₂ concentration, and the DO₂ concentration has been determined by fitting the HO₂ decays, now governed by their reaction with DO₂, to the rate constant k₁. A rate constant with insignificant pressure dependence was found: k₂ = (4.1 ± 0.6) × 10⁻¹³ (1 + (2 ± 2) × 10⁻²⁰ cm³ × [He] cm⁻³) cm³ s⁻¹ as well as an increase of k₂ with increasing D₂O concentration was observed: k₂ = (4.14 ± 0.02) × 10⁻¹³ × (1 + (6.5 ± 1.3) × 10⁻¹⁸ cm³ × [D₂O] cm⁻³) cm³ s⁻¹. The result for k₂ is in excellent agreement with literature values, whereas this is the first determination of k₁.     

Hydroperoxyl Radicals (HOO.): Vitamin E Regeneration and H‐Bond Effects on the Hydrogen Atom Transfer

Hydroperoxyl (HOO^.) and alkylperoxyl (ROO^.) radicals show a different behavior in H‐atom‐transfer processes. Both radicals react with an analogue of α‐tocopherol (TOH), but HOO^., unlike ROO^., is able to regenerate TOH by a fast H‐atom transfer: TO^.+HOO^.→TOH+O₂. The kinetic solvent effect on the H‐atom transfer from TOH to HOO^. is much stronger than that observed for ROO^. because noncovalent interactions with polar solvents (Solv???HOO^.) destabilize the transition state.     

Reactions of hydroxyl (HO•) and hydroperoxyl (HO) radicals generated chemically and photochemically with poly(ethylene oxide)

Poly(ethylene oxide) (poly(oxy-1,2-ethanediyl) is rapidly oxidized by hydroxyl (HO^?) and hydroperoxyl (HO) radicals generated by photolysis of hydrogen peroxide (H₂O₂) or by the catalytic decomposition of H₂O₂ by metallic silver. This process is accompanied by a chain scission during which the molecular weight decreases and the polydispersity changes. As a result of this process, the crystalline structure of poly(ethylene oxide) disappears, and the polymer becomes completely amorphous. © 1995 John Wiley & Sons, Inc.     

Experimental and theoretical investigation of the reaction of RO2 radicals with OH radicals: Dependence of the HO2 yield on the size of the alkyl group

The HO₂ yield in the reaction of peroxy radicals with OH radicals has been determined experimentally at 50 Torr helium by measuring simultaneously OH and HO₂ concentration time profiles, following the photolysis of XeF₂ in the presence of different hydrocarbons and O₂. The following yields have been obtained:  = (0.90 ± 0.1),  = (0.75 ± 0.15),  = (0.41 ± 0.08), and  = (0.15 ± 0.03). The clear decrease in HO₂ yield with increasing size of the alkyl moiety can be explained by an increased stabilization of the trioxide adduct, ROOOH. This has been confirmed by ab initio and Rice–Ramsperger–Kassel–Marcus master equation calculations. Extrapolation of the experimental results to atmospheric conditions shows that the stabilized adduct, ROOOH, is the nearly exclusive product of the reaction between OH radicals and peroxy radicals containing more than three C‐atoms. The fate and possible impact of these species is completely unexplored so far.     

Insight into the reaction mechanism of CH2SH with HO2: A density functional theory study

Density functional theory was adopted in this work to reveal the reaction mechanism of CH₂SH with HO₂. Reaction rate constants were computed from 200 to 2000 K using the transition state theory combined with Wigner and Eckart tunneling correction. Moreover, localized orbital locator, atoms in molecules and Mayer bond order analyses were used to study the essence of chemical bonding evolution. Eleven singlet paths and three triplet ones are located on the potential surface (PES). The results show that the main products on the singlet PES are ¹CH₂S and H₂O₂, whereas on the triplet PES they are CH₃SH + ³O₂, which are coincident with the similar reaction of CH₃S and HO₂. This conclusion is also supported by rate constant calculation results. Interestingly, all the possible paths are involved in the hydrogen transfer. The results have provided underlying insights to the analogous reactions and further experimental studies.     

硫代草酸异构体结构及异构化反应机理的理论研究

采用量子化学CBS-QB3组合方法对硫代草酸可能存在的异构体构型及异构体间相互转化机理进行了详细计算研究,分别得到11种稳定结构及12种异构化过渡态。其中硫代草酸异构体的相对稳定性顺序为M11M7M10M1M9M6M2M3=M4M5,不稳定异构体M5极易向稳定异构体转化。异构体M6向M11转化仅需越过1.92k J·mol-1的能垒,且放出49.04k J·mol-1能量,因此M6向M11的转化是H迁移异构化反应的主通道。     

杂萘联苯共聚醚砜的非均相磺化

以杂萘联苯共聚醚砜(PPHES)为原料,氯仿为溶剂,浓硫酸为磺化试剂,采用非均相磺化法对PPHES进行了磺化改性,得到了一系列不同磺化度的磺化杂萘联苯共聚醚砜(SPPHES).考察了浓硫酸浓度、磺化反应温度和时间等工艺条件对产物磺化度的影响.利用FT-IR、1H-NMR对SPPHES进行了表征.结果表明,磺酸基已成功引...