通过OH拉伸模式的选择性红外辐射揭示非晶态固体水的表面结构
Unveiling the Surface Structure of Amorphous Solid Water via Selective Infrared Irradiation of OH Stretching Modes
摘要：
在探索生命的形成过程中，非晶态固体水（ASW）是研究最广泛的分子系统之一。事实上，ASW在冷星际介质（ISM）中无处不在，ASW涂层的尘埃颗粒为固相化学提供了催化表面，并且被认为存在于地球大气层的高海拔地区。已经表明，冰表面吸附诸如CO、N $_2$或CH $_4$的小分子，最可能是在表面悬挂的OH基团上。我们的研究提出了全新的见解ASW的行为后，选择性红外（IR）照射其悬挂模式。当照射时，这些表面H $_2$ O分子重组，主要在冰表面上形成稳定的单体状水模式。我们表明，我们系统地挑起“烧孔”效应（或净损失的振荡器）在照射波长和再生相同的吸收水单体的ASW表面上。我们的研究表明，所有悬挂模式共享一个共同的振动弛豫通道;冰保持无定形，但结合位点的范围减少，从而改变了催化能力。
英文摘要：
In the quest to understand the formation of the building blocks of life, amorphous solid water (ASW) is one of the most widely studied molecular systems. Indeed, ASW is ubiquitous in the cold interstellar medium (ISM), where ASW-coated dust grains provide a catalytic surface for solid phase chemistry, and is believed to be present in the Earth's atmosphere at high altitudes. It has been shown that the ice surface adsorbs small molecules such as CO, N$_2$, or CH$_4$, most likely at OH groups dangling from the surface. Our study presents completely new insights concerning the behaviour of ASW upon selective infrared (IR) irradiation of its dangling modes. When irradiated, these surface H$_2$O molecules reorganise, predominantly forming a stabilised monomer-like water mode on the ice surface. We show that we systematically provoke "hole-burning" effects (or net loss of oscillators) at the wavelength of irradiation and reproduce the same absorbed water monomer on the ASW surface. Our study suggests that all dangling modes share one common channel of vibrational relaxation; the ice remains amorphous but with a reduced range of binding sites, and thus an altered catalytic capacity.
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