Autoionization in liquid water

The dissociation of a water molecule in liquid water is the fundamental event in acid-base chemistry, determining the pH of water. Because of the short time scales and microscopic length scales involved, the dynamics of this autoionization have not been directly probed by experiment. Here, the autoionization mechanism is revealed by sampling and analyzing ab initio molecular dynamics trajectories. We identify the rare fluctuations in solvation energies that destabilize an oxygen-hydrogen bond. Through the transfer of protons along a hydrogen bond "wire," the nascent ions separate by three or more neighbors. If the hydrogen bond wire connecting the two ions is subsequently broken, a metastable charge-separated state is visited. The ions may then diffuse to large separations. If, however, the hydrogen bond wire remains unbroken, the ions recombine rapidly. Because of their concomitant large electric fields, the transient ionic species produced in this case may provide an experimentally detectable signal of the dynamics we report.     

The spatial structure in liquid water

Liquid state structure has traditionally been characterized with the radial distribution functions between atoms. Although these functions are routinely available from x-ray diffraction and neutron scattering experiments or from computer simulations, they cannot be interpreted unambiguously to provide the spatial order in a molecular liquid. A direct approach to determining the spatial structure in the liquid state is demonstrated here. Three-dimensional maps representing the local atomic densities are presented for several water models. These spatial maps provide a picture of the short-range order in liquid water which reveals specific details of its local structure that are important in the understanding of its properties.     

"Polywater": Possibility of p-Electron Delocalization

p-Electron delocalization may be important in determining the stability of the symmetric hydrogen bonds in a recently proposed model of "polywater."     

Mars: occurrence of liquid water

In the absence of juvenile liquid water, condensation of water vapor to ice and subsequent melting of ice are the only means of producing liquid water on the martian surface. However, the evaporation rate is so high that the available heat sources cannot melt pure ice. Liquid water is therefore limited to concentrated solutions of strongly deliquescent salts.     

Energetics of hydrogen bond network rearrangements in liquid water

A strong temperature dependence of oxygen K-edge x-ray absorption fine structure features was observed for supercooled and normal liquid water droplets prepared from the breakup of a liquid microjet. Analysis of the data over the temperature range 251 to 288 kelvin (-22 degrees to +15 degrees C) yields a value of 1.5 +/- 0.5 kilocalories per mole for the average thermal energy required to effect an observable rearrangement between the fully coordinated ("ice-like") and distorted ("broken-donor") local hydrogen-bonding configurations responsible for the pre-edge and post-edge features, respectively. This energy equals the latent heat of melting of ice with hexagonal symmetry (ice Ih) and is consistent with the distribution of hydrogen bond strengths obtained for the "overstructured" ST2 model of water.     

Inorganic liquid photovoltaic cell: tetravalent molybdenum in water

An inorganic liquid photovoltaic cell is described. The cell is based on the reaction 2Mo(4+) <--> Mo(5+) + Mo(3+), with pentavalent molybdenum formed in the illuminated half-cell and trivalent molybdenum formed in the dark half-cell. In the photochemical reaction pentavalent molybdenum precipitates. Consequently, the cell has the capability of storing energy.     

The structure of the first coordination shell in liquid water

X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen-bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen-bonded tetrahedral structure in ice. Upon heating from 25 degrees C to 90 degrees C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen-bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed.     

Negligible effect of ions on the hydrogen-bond structure in liquid water

The effects of ions on bulk properties of liquid water, such as viscosity, have suggested that ions alter water's hydrogen-bonding network. We measured the orientational correlation time of water molecules in Mg(ClO4)2, NaClO4, and Na2SO4 solutions by means of femtosecond pump-probe spectroscopy. The addition of ions had no influence on the rotational dynamics of water molecules outside the first solvation shells of the ions. This result shows that the presence of ions does not lead to an enhancement or a breakdown of the hydrogen-bond network in liquid water.     

Density maxima in high-pressure supercooled water and liquid silicon dioxide

With glass capillary pressure vessels it has been possible to study the effect of pressure on the temperature of maximum density (TMD) and on the "sharpness" of the density maximum in liquid H(2)O and D(2)O in the important but little-studied supercooled regime. A pressure of 1200 bars produces a 33 degrees C depression of the TMD in these liquids and a considerable reduction in sharpness. Comparison with the rather flat density maximum for liquid SiO(2) supports the notion that the presence or absence of density anomalies in "tetrahèdral" liquids depends on the average bridge-bond angle, which is evidently unusually large in water at normal pressure.     

谐振式液位传感器在喷雾机药液箱液位检测中的应用

分析了洗衣机用谐振式液位传感器的工作原理及其相对于其他液位检测设备的优势,针对将其用于车载大型喷雾机药液箱时在测量范围上的不足,通过结构改进使测量范围由原来的600 mm增加到1 200 mm;在选用AVR系列单片机ATmega8作为测量用处理器的基础上,开发了测量电路和相应的程序;通过安装设计,有效地避免了液位大幅度抖动而损坏传感器的风险。结果表明,传感器系统量程符合要求,液位高度与传感器输出信号频率的决定系数R2为0.989。     

液态悬浮大量元素水溶肥生产技术

液体悬浮大量水溶肥料可施用于多种作物、果树中,具有提高施肥效率,降低成本,便捷操作等效果。介绍液态悬浮大量元素水溶肥的定义与生产要求,并总结其生产工艺流程操作与检测等方面内容。     

Formation of cyclic water hexamer in liquid helium: the smallest piece of Ice

The cyclic water hexamer, a higher energy isomer than the cage structure previously characterized in the gas phase, was formed in liquid helium droplets and studied with infrared spectroscopy. This isomer is formed selectively as a result of unique cluster growth processes in liquid helium. The experimental results indicate that the cyclic hexamer is formed by insertion of water molecules into smaller preformed cyclic complexes and that the rapid quenching provided by the liquid helium inhibits its rearrangement to the more stable cage structure.     

高效液相色谱-串联质谱法测定水中全氟辛烷磺酸含量

建立了水中全氟辛烷磺酸(perfluoro-rooctane sulfonate, PFOS)的高效液相色谱-串联质谱法分析方法。用0.22μm PP滤膜过滤水样,Poly-Sery HLB固相萃取柱对200 mL水样进行富集处理,以质量分数为10%的甲醇水溶液淋洗HLB柱以去除表面杂质,随后抽真空,再用4 mL纯甲醇溶液洗脱HLB柱。取洗脱液上机检测,以质量分数为0.1%的甲酸为流动相A,甲醇为流动相B,采用ACQΜITYΜPLC BEH C₁₈色谱柱对洗脱液进行分离,负离子多反应监测模式检测,碎片离子m/z=80,内标法定量分析。在优化条件下,PFOS在0.01～50μg/L范围内线性较好,相关系数r>0.99,方法检出限为0.25μg/L。方法加标回收实验添加浓度0.2、2.0和20μg/L,PFOS加标回收率为82.1%～104.5%,相对标准偏差(RSD)为2.34%～5.64%。采集湖泊及养殖虾塘进出口水样进行测定,其PFOS含量均低于检出限,其中,湖水加标回收率为84.75%～112.2%,RSD<5.62%,养殖塘水样加标回收率为81....     

水肥液膜配合对玉米生物学特性及水分利用效率的影响

玉米节水节肥高产研究对保障粮食安全具有重要现实意义,本研究供试玉米品种为‘郑单958’,采用旱棚盆栽试验,研究液膜覆盖、灌水与施肥对夏玉米生物学特性、产量及水分利用效率的影响。结果表明:在欠水条件(200mm)与贫水条件(300mm)下,液膜覆盖促进夏玉米生长发育的效果显著,L3水平(液膜45kg/hm~2)玉米株高和叶面积指数比L1水平(无液膜)分别增加了33.88%,36.07%,产量增加53.77%,20.76%;平水(400mm)、丰水条件(500mm)下,夏玉米株高、茎粗与叶面积指数在全生育期均高于欠水、贫水处理,并且产量显著高于欠水、贫水处理,水、肥、液膜对夏玉米生物学特性及产量的影响为:W(水分)F(施肥)L(液膜);以C11(W3F3L1)处理玉米茎粗、叶面积指数、产量均为最高,分别为20.2mm,5.86,148.83g/pot。综上,在缺水条件下,喷施液态膜可提高玉米水分利用效率,最高达28.18kg/(mm·hm~2);水分充足时夏玉米高产高效的最优方案为:W3(400mm)+F3(N-P-K:180-120-135kg/hm~2)+L1(液膜0kg/hm~2)。     

固相萃取-高效液相色谱法优化测定 饮用水中的微囊藻毒素

对流动相酸度,洗脱速度和色谱柱柱温进行了优化,建立了一个非常适用于检测饮用水中微囊藻毒素 LR 的分析方法,该方法用0.04%TFA/乙腈,63,37,为流动相,洗脱时间为7 min,该方法具有温和,快速,经济,适用等 特点,经过对广东省某典型水库的微囊藻毒素进行检测分析,结果表明院该方法定量可靠,准确、灵敏,回收率为 88%,最低检出限为0.05 滋g/L.