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首页> 外文期刊>Analytical chemistry >A Strategy for Single Supersaturated Droplet Analysis: Confocal Raman Investigations on the Complicated Hygroscopic Properties of Individual MgSO_(4) Droplets on the Quartz Substrate
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A Strategy for Single Supersaturated Droplet Analysis: Confocal Raman Investigations on the Complicated Hygroscopic Properties of Individual MgSO_(4) Droplets on the Quartz Substrate

机译：单个过饱和液滴分析的策略：石英衬底上单个MgSO_（4）液滴的复杂吸湿特性的共聚焦拉曼研究

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摘要

We report a new strategy for single supersaturated droplet analysis, i.e., the complicated hygroscopic properties of MgSO_(4) aerosols under supersaturated state were studied through the micro-Raman observation on an individual MgSO_(4) droplet deposited on a quartz substrate in a relative-humidity-controlled chamber. Upon reduction of the ambient relative humidity (RH), MgSO_(4) droplets with tiny volume lost water but did not effloresce. Thus, a detailed spectral evolution of the symmetric stretching vibration band (v_(1)-SO_(4~(2-))) from free ions (at approx983 cm~(-1)) to monodentate (approx995 cm~(-1)) and then to bidentate contact ion pairs (CIPs) or more complex chain-structural compositions (approx1021 cm~(-1)) was observed with the high signal-to-noise (S/N) confocal Raman spectra of the droplet with a diameter of approx80 microns. Such a transition process could be well-described by the changes of relative intensity at 983, 995, and 1021 cm~(-1). Four steps, i.e., concentrated step, monodentate CIPs step, bidentate CIPs step, and gel step, were roughly observed in the dehumidifying-humidifying cycle according to the intensity ratios of I_(995)/I_(983) and I_(1021)/I_(983). Even though the area ratio of the O-H stretching band of water molecules to the v_(1)-SO_(4~(2-)) band seemed reversible in the dehumidifying and humidifying processes, the intensity ratios of I_(995)/I_(983) and I_(1021)/I_(983) showed a hysteresis in the decomposition of CIPs in the humidifying process with the RH < 40percent. The O-H stretching envelope of the MgSO_(4) droplet was also observed to be sensitive to the structural changes of the hydrogen bonding of water molecules in the four steps. The intensity ratio of Raman scattering for the components with strong hydrogen bonds to those with weak ones, i.e., I_(3224)/I_(3431), was used to understand the effects of CIPs on the water structures of the first hydration layer of Mg~(2+). Good consistency on the hysteresis in the humidifying process was also observed from the ratio of I_(3224)/I_(3431) changing with RH.
机译：我们报告了一种用于单个过饱和液滴分析的新策略，即，通过微拉曼观测法对沉积在石英衬底上的单个MgSO_（4）液滴的相对拉曼光谱进行了研究，研究了过饱和状态下MgSO_（4）气溶胶的复杂吸湿性能。 -湿度控制室。降低环境相对湿度（RH）后，体积很小的MgSO_（4）液滴会失水，但不会起花。因此，对称拉伸振动带（v_（1）-SO_（4〜（2-）））从自由离子（大约983 cm〜（-1））到单齿（大约995 cm〜（-1）的详细光谱演化）），然后用液滴的高信噪比（S / N）共焦拉曼光谱观察到接触离子对（CIP）或更复杂的链结构组成（约1021 cm〜（-1））直径约80微米。这种转变过程可以通过在983、995和1021 cm〜（-1）处的相对强度变化来很好地描述。根据I_（995）/ I_（983）和I_（1021）/的强度比，在除湿加湿循环中大致观察到了浓缩步骤，单齿CIP步骤，双齿CIP步骤和凝胶步骤四个步骤。我_（983）。尽管在除湿和加湿过程中水分子的OH拉伸带与v_（1）-SO_（4〜（2-））带的面积比似乎是可逆的，但I_（995）/ I_（ 983）和I_（1021）/ I_（983）在RH <40％的加湿过程中在CIP的分解中显示出滞后现象。在四个步骤中，还观察到MgSO_（4）液滴的O-H拉伸包膜对水分子氢键的结构变化敏感。用氢键强的组分与氢键弱的组分的拉曼散射强度比，即I_（3224）/ I_（3431），来了解CIPs对镁第一水化层水结构的影响。 〜（2+）。从I_（3224）/ I_（3431）随RH变化的比率，还观察到加湿过程中的磁滞具有良好的一致性。

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