极地冰中的热H/D交换-空间中的氘扰乱
Thermal H/D exchange in polar ice - deuteron scrambling in space
摘要：
通过测量H $_2$ O、HDO和D $_2$ O的特征振动弯曲模强度随时间和温度的变化，研究了混合非晶H $_2$ O：D $_2$ O中的热诱导质子/氘交换.实验已经进行了使用超高真空设置配备了红外光谱仪，用于调查的光谱演变均匀混合的冰共沉积在薄膜时，在90至140 K域的温度。用这种非能量检测方法，我们发现一个显着较低的活化能H/D交换- $3840 \pm 125$ K -比以前报道的。这很可能是由于所涉及的星际冰类似物的无定形性质。这提供了反应时间尺度（$T$ $>70$ K的$τ<10^4$年）足够快，使该过程在星际环境中变得重要。因此，D $_2$ O的天文探测将更具挑战性，因为它有可能与H $_2$ O反应形成HDO。此外，额外的实验，以及以前的研究表明，质子/氘核交换也发生在水与其他氢键分子的冰混合物中，特别是在OH和NH部分。我们的结论是，H/D交换冰是一个更普遍的过程，应纳入冰模型，适用于原行星盘或模拟变暖的彗星冰在其通过近日点，检查其影响的程度上的最终氘氢比。
英文摘要：
We have investigated the thermally induced proton/deuteron exchange in mixed amorphous H$_2$O:D$_2$O ices by monitoring the change in intensity of characteristic vibrational bending modes of H$_2$O, HDO, and D$_2$O with time and as function of temperature. The experiments have been performed using an ultra-high vacuum setup equipped with an infrared spectrometer that is used to investigate the spectral evolution of homogeneously mixed ice upon co-deposition in thin films, for temperatures in the 90 to 140 K domain. With this non-energetic detection method we find a significantly lower activation energy for H/D exchange -- $3840 \pm 125$ K -- than previously reported. Very likely this is due to the amorphous nature of the interstellar ice analogues involved. This provides reactive timescales ($τ<10^4$ years at $T$ $>70$ K) fast enough for the process to be important in interstellar environments. Consequently, an astronomical detection of D$_2$O will be even more challenging because of its potential to react with H$_2$O to form HDO. Furthermore, additional experiments, along with previous studies, show that proton/deuteron swapping also occurs in ice mixtures of water with other hydrogen bonded molecules, in particular on the OH and NH moieties. We conclude that H/D exchange in ices is a more general process that should be incorporated into ice models that are applied to protoplanetary disks or to simulate the warming up of cometary ices in their passage of the perihelion, to examine the extent of its influence on the final deuteron over hydrogen ratio.
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