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Energy Transfer in Amorphous Solid Water: Light-Mediated Expulsion of N2o4 Guest Molecules

机译：非晶态固体水中的能量转移：N2o4客体分子的光介导排出

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摘要

Molecular transport and morphological change were examined in films of vapor-deposited amorphous solid water, H2O(as). A buried N2O4 layer absorbs pulsed 266-nm radiation, creating heated fluid. Temperature and pressure gradients facilitate the formation of fissures through which fluid travels to vacuum. Film thickness up to 1440 Langmuirs was examined. In all cases, transport to vacuum could be achieved with a single pulse. Material that entered vacuum was detected using a time-of-flight mass spectrometer that recorded spectra every 10 mus. An amorphous solid water layer insulated the N2O4 layer from the high-thermal-conductivity MgO(100) substrate; this was verified experimentally and with heat transfer calculations. Laser-heated fluid strips water from fissure walls throughout its trip to vacuum. Experiments with alternate H2O(as) and D2O(as) layers reveal efficient isotope scrambling, consistent with water reaching vacuum via this mechanism. It is likely that ejected water undergoes collisions just above the film surface due to the high density of material that reaches the surface via fissures. Little material enters vacuum after cessation of the 10 ns pulse because cold amorphous solid water near the film surface freezes material that is no longer being heated. A proposed model is in accord with the data. A commercial program (COMSOL Multiphysics(c)) was used to simulate the heat transfer behavior of a multi-component system comprising solid N2O4 and ASW strata supported by a MgO substrate, wherein the application of heat to the amorphous solid water occurs via transfer from the N2O4. The N2O4 layer is heated, and the system is allowed to evolve. The transience of elevated temperatures is consistent with transmission Fourier-transform infrared spectroscopy of the films before and after irradiation, together leading us to conclude that crystallization does not occur in the amorphous solid water upon irradiation of the guest molecules. The time for heat to travel to the surface of an H2O(as)/N2O4/H2O(as) sample with a thick upper layer argues for material transport via fissures, and not via surface evaporation.
机译：在汽相沉积的无定形固体水H2O（as）的膜中检查了分子迁移和形态变化。掩埋的N2O4层吸收266 nm的脉冲辐射，产生加热的流体。温度和压力梯度有助于形成裂缝，流体通过裂缝传播到真空中。检查了直至1440 Langmuirs的膜厚。在所有情况下，都可以通过单个脉冲实现向真空的传输。使用飞行时间质谱仪检测进入真空的材料，该质谱仪每10毫秒记录一次光谱。非晶态固体水层使N2O4层与高导热MgO（100）衬底绝缘；这已经通过实验和传热计算得到了验证。激光加热的流体在其通向真空的整个过程中都会从裂隙壁上剥离水。在交替的H2O（as）和D2O（as）层上进行的实验表明，同位素加扰有效，这与通过此机制达到真空的水相一致。由于通过裂缝到达表面的高密度材料，喷射的水很可能在薄膜表面上方发生碰撞。停止10 ns脉冲后，几乎没有材料进入真空，因为薄膜表面附近的冷非晶态固态水冻结了不再加热的材料。提出的模型与数据相符。使用商业程序（COMSOL Multiphysics（c））模拟由MgO基质支撑的固体N2O4和ASW地层组成的多组分系统的传热行为，其中热量通过从N2O4。加热N2O4层，并允许系统析出。高温的瞬变与辐照前后薄膜的透射傅立叶变换红外光谱一致，一起使我们得出结论，在客体分子辐照下，非晶态固体水中不会发生结晶。热量传播到上层较厚的H2O（as）/ N2O4 / H2O（as）样品表面的时间表明，材料是通过裂缝而不是通过表面蒸发来传递的。

著录项

  • 作者

    McKean, Stephanie Anne.;

  • 作者单位

    University of Southern California.;

  • 授予单位 University of Southern California.;
  • 学科 Molecular chemistry.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 140 p.
  • 总页数 140
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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