Differential adsorption of complex organic molecules isomers at interstellar ice
Differential adsorption of complex organic molecules isomers at interstellar ice
复制标题
星际冰中复杂有机分子异构体的差异吸附
DOI：
10.1051/0004-6361/201016184
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发表时间：
2011
期刊：
影响因子：
56.9
通讯作者：
Y. Ellinger
中科院分区：
文献类型：
--
作者：
M. Lattelais;M. Bertin;H. Mokrane;C. Romanzin;X. Michaut;P. Jeseck;J. Fillion;H. Chaabouni;E. Congiu;F. Dulieu;S. Baouche;J. Lemaire;F. Pauzat;J. Pilmé;C. Minot;Y. Ellinger
上下文在星际和星周介质中检测到的约150种不同物种中，有20多种也是在冰冷的环境中发现的。对于目前在星际介质中观测到的大多数物种，给定化学式的最丰富的异构体是最稳定的异构体（最小能量原理- MEP），只有少数例外，例如CH 3COOH/HCOOCH 3和CH 3CH 2 OH/CH 3 OCH 3，它们的形成被认为发生在星际颗粒的冰冷地幔上。
目标。我们调查分子冰和周围的气相的组合物中发现的差异是否可以起源于一个异构体从另一个在冰表面的吸附之间的差异。
方法.本文对上述四种分子，即乙酸（AA）/甲酸甲酯（MF）和乙醇（EtOH）/二甲醚（DME）在水冰表面的低温吸附能进行了系统的理论和实验研究。这个问题首先在LCT理论上解决，使用固态周期密度泛函理论（DFT）来表示有组织的固体载体。然后由LPMAA和LERMA/LAMAp的两个团队在70和160 K之间的超高真空（UHV）下使用程序升温脱附（TPD）独立地进行冰/分子相互作用能的实验测定。
结果对于每对异构体，理论和实验都同意，最稳定的异构体（AA或EtOH）与水冰的相互作用比更高能量的异构体（MF或DME）更有效。这种差异吸附可以清楚地看出，在不同的解吸温度的异构体。这与它们的内在稳定性无关，而是与AA和EtOH与冰表面产生更多更强的氢键有关。
结论.我们发现，氢键可能发挥重要作用，从谷物中释放的有机物种，并建议，根据环境的不同，不应拒绝差分吸附作为一种可能的方式来解释MEP例外。
Context. Over 20 of the ~150 different species detected in the interstellar and circumstellar media have also been identified in icy environments. For most of the species observed so far in the interstellar medium (ISM), the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle – MEP) with few exceptions such as, for example, CH3COOH/HCOOCH3 and CH3CH2OH/CH3OCH3, whose formation is thought to occur on the icy mantles of interstellar grains.
Aims. We investigate whether differences found in the compositions of molecular ices and the surrounding gas phase could originate from differences between the adsorption of one isomer from that of another at the ice surface.
Methods. We performed a coherent and concerted theoretical/experimental study of the adsorption energies of the four molecules mentioned above, i.e. acetic acid (AA)/methyl formate (MF) and ethanol (EtOH)/dimethyl ether (DME) on the surface of water ice at low temperature. The question was first addressed theoretically at LCT using solid state periodic density functional theory (DFT) to represent the organized solid support. The experimental determination of the ice/molecule interaction energies was then carried out independently by two teams at LPMAA and LERMA/LAMAp using temperature programmed desorption (TPD) under an ultra-high vacuum (UHV) between 70 and 160 K.
Results. For each pair of isomers, theory and experiments both agree that the most stable isomer (AA or EtOH) interacts more efficiently with the water ice than the higher energy isomer (MF or DME). This differential adsorption can be clearly seen in the different desorption temperatures of the isomers. It is not related to their intrinsic stability but instead to both AA and EtOH producing more and stronger hydrogen bonds with the ice surface.
Conclusions. We show that hydrogen bonding may play an important role in the release of organic species from grains and propose that, depending on the environment, differential adsorption should not be rejected as a possible way of interpreting MEP exceptions.