Kumi G, Malyk S, Hawkins S, Reisler H, Wittig C
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
J Phys Chem A. 2006 Feb 16;110(6):2097-105. doi: 10.1021/jp058234y.
Guest-host interactions have been examined experimentally for amorphous solid water (ASW) films doped with CO2 or N2O. The main diagnostics are Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD). ASW films deposited at 90 K are exposed to a dopant, and the first molecules that attach to a film enter its bulk until it is saturated with them. Subsequent dopant adsorption results in crystal growth atop the ASW film. There are distinct spectral signatures for these two cases: LO and TO vibrational modes for the crystal overlayer, and an easily distinguished peak for dopant molecules that reside within the ASW film. Above 105 K, the dopant surface layer desorbs fully. Some dopants residing within the ASW film remain until 155 K, at which point the ASW-to-crystalline-ice transition occurs, expelling essentially all of the dopant. No substantial differences are observed for CO2 versus N2O. It is shown that annealing an ASW film to 130 K lowers the film's capacity to include dopants by a factor of approximately 3, despite the fact that the ASW spectral feature centered at approximately 3250 cm(-1) shows no discernible change. Sandwiches were prepared: ASW-dopant-ASW etc., with the dopant layer displaying crystallinity. Raising these samples past 105 K resulted in the expulsion of essentially all of the crystalline dopant. What remained displayed the same spectral signature as the molecules that entered the bulk following adsorption at the surface. It is concluded that the adsorption sites, though prepared differently, have a lot in common. Dangling OH bonds were observed. When they interacted with a dopant, they underwent a red shift of approximately 50 cm(-1). This is in qualitative agreement with studies that have been carried out with weakly bound binary complexes. As a result of this study, a fairly complete, albeit qualitative, picture is in place for the adsorption, binding, and transport of CO2 and N2O in ASW films.
已通过实验研究了掺杂二氧化碳或一氧化二氮的非晶态固体水（ASW）薄膜中的客体-主体相互作用。主要诊断方法是傅里叶变换红外（FTIR）光谱和程序升温脱附（TPD）。在90 K下沉积的ASW薄膜暴露于掺杂剂，首先附着在薄膜上的分子会进入其主体，直到主体被它们饱和。随后的掺杂剂吸附会导致在ASW薄膜顶部形成晶体生长。这两种情况有明显的光谱特征：晶体覆盖层的LO和TO振动模式，以及ASW薄膜内掺杂剂分子的一个易于区分的峰。在105 K以上，掺杂剂表面层完全脱附。一些存在于ASW薄膜内的掺杂剂会一直存在到155 K，此时发生ASW向结晶冰的转变，基本上排出了所有掺杂剂。对于二氧化碳和一氧化二氮，未观察到实质性差异。结果表明，将ASW薄膜退火至130 K会使薄膜容纳掺杂剂的能力降低约3倍，尽管以约3250 cm(-1)为中心的ASW光谱特征没有明显变化。制备了夹心结构：ASW-掺杂剂-ASW等，其中掺杂剂层显示出结晶性。将这些样品加热到105 K以上会导致基本上所有结晶掺杂剂被排出。剩余部分显示出与在表面吸附后进入主体的分子相同的光谱特征。得出的结论是，吸附位点尽管制备方式不同，但有很多共同之处。观察到了悬空的OH键。当它们与掺杂剂相互作用时，会发生约50 cm(-1)的红移。这与对弱结合二元配合物进行的研究在定性上是一致的。作为这项研究的结果，对于二氧化碳和一氧化二氮在ASW薄膜中的吸附、结合和传输，已经形成了一个相当完整（尽管是定性的）的图景。
