Malyk S, Kumi G, Reisler H, Wittig C
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
J Phys Chem A. 2007 Dec 27;111(51):13365-70. doi: 10.1021/jp074083i. Epub 2007 Nov 30.
Interactions of 13CO2 guest molecules with vapor-deposited porous H2O ices have been examined using temperature-programmed desorption (TPD) and Fourier transform infrared (FTIR) techniques. Specifically, the trapping and release of 13CO2 by amorphous solid water (ASW) has been studied. The use of 13CO2 eliminates problems with background CO2. Samples were prepared by (i) depositing 13CO2 on top of ASW, (ii) depositing 13CO2 underneath ASW, and (iii) codepositing 13CO2 and H2O during ASW formation. Some of the deposited 13CO2 becomes trapped when the ice film is annealed. The amount of 13CO2 trapped in the film depends on the deposition method. The release of trapped molecules occurs in two stages. The majority of the trapped 13CO2 escapes during the ASW-to-cubic ice phase transition at 165 K, and the rest desorbs together with the cubic ice film at 185 K. We speculate that the presence of 13CO2 at temperatures up to 185 K is due to 13CO2 that is trapped in cavities within the ASW film. These cavities are similar to ones that trap the 13CO2 that is released during crystallization. The difference is that 13CO2 that remains at temperatures up to 185 K does not have access to escape pathways to the surface during crystallization.
利用程序升温脱附（TPD）和傅里叶变换红外（FTIR）技术研究了13CO2客体分子与气相沉积的多孔H2O冰之间的相互作用。具体而言，研究了非晶态固体水（ASW）对13CO2的捕获和释放。使用13CO2消除了背景CO2带来的问题。样品通过以下方式制备：（i）将13CO2沉积在ASW之上，（ii）将13CO2沉积在ASW之下，以及（iii）在ASW形成过程中共沉积13CO2和H2O。当冰膜退火时，一些沉积的13CO2会被捕获。捕获在膜中的13CO2的量取决于沉积方法。捕获分子的释放分两个阶段发生。大部分捕获的13CO2在165 K的ASW到立方冰相变过程中逸出，其余的则在185 K时与立方冰膜一起解吸。我们推测，在高达185 K的温度下13CO2的存在是由于其被困在ASW膜内的空洞中。这些空洞类似于捕获在结晶过程中释放的13CO2的空洞。不同之处在于，在高达185 K的温度下仍存在的13CO2在结晶过程中无法获得通向表面的逃逸途径。
