School of Chemistry and Biochemistry, Georgia Institute of Technology , 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States.
J Phys Chem A. 2014 Feb 20;118(7):1228-36. doi: 10.1021/jp4042815. Epub 2014 Feb 7.
Lyman-α (121.6 nm) photon and 1 keV electron-beam irradiation of pure HCONH2 (FA) ice and H2O:HCONH2 ice mixtures on high-surface-area SiO2 nanoparticles have been investigated with FT-IR spectroscopy and temperature programmed desorption (TPD). Lyman-α photolysis of pure amorphous FA ice grown at 70 K and crystalline FA ice produced by annealing to 165 K gives spectral signatures between 2120 and 2195 cm(-1) that we assign primarily to OCN(-) and CO. The OCN(-) and CO yields are ∼25% less abundant for crystalline FA ice. Photon and electron processing also produces H2 that is released from the ice between ∼90 and 140 K. A decrease in the H2 TPD peak is seen for irradiated crystalline HCONH2 ice. Lyman-α photolysis of H2O:HCONH2 mixed ices increases OCN(-) and CO production, suggesting a catalytic role of H2O. Also, for pure FA, 1 keV electron irradiation slightly increases the yield of OCN(-), while CO decarboxylation is selectively prevented. CO is also not produced in H2O:HCONH2 ices upon electron irradiation. Dissociative ionization, direct dissociative excitation, and dissociative electron attachment (DEA) channels are accessible in the Lyman-α (121.6 nm) photon and 1 keV electron-beam energy range. DEA energetically favors OCN(-) and H(-) formation, with the latter leading to H2 formation. The FA fragment product identities, yields, and branching ratios are considerably different relative to the gas phase and depend upon the radiation type, ice structure, and the presence of SiO2 nanoparticles. The latter may increase ion-electron recombination and radical recombination rates. The main products observed suggest very different condensed-phase dissociation channels from those reported for gas-phase dissociation. Formation of ions/products from FA is not negligible upon Lyman-α photolysis or electron irradiation, both of which could process ices in interstellar regions as well as in Titan's atmosphere.
用傅里叶变换红外光谱（FT-IR）和程序升温脱附（TPD）研究了 Lyman-α（121.6nm）光子和 1keV 电子束辐照纯 HCONH2（FA）冰和 H2O:HCONH2 冰混合物在高表面积 SiO2 纳米颗粒上的情况。在 70K 下生长的非晶态 FA 冰和在 165K 退火生成的晶态 FA 冰的 Lyman-α光解产生了 2120 到 2195cm-1 之间的光谱特征，我们主要将其归因于 OCN-和 CO。对于晶态 FA 冰，OCN-和 CO 的产率要低 25%。光子和电子处理还会产生氢气，这些氢气在 90 到 140K 之间从冰中释放出来。辐照晶态 HCONH2 冰时，H2 的 TPD 峰会下降。H2O:HCONH2 混合冰的 Lyman-α光解增加了 OCN-和 CO 的产生，表明 H2O 具有催化作用。此外，对于纯 FA，1keV 电子辐照略微增加了 OCN-的产率，而 CO 的脱羧反应则被选择性地阻止。在电子辐照下，H2O:HCONH2 冰中也不会产生 CO。在 Lyman-α（121.6nm）光子和 1keV 电子束能量范围内，可以通过离解电离、直接离解激发和离解电子俘获（DEA）通道进行反应。DEA 在能量上有利于 OCN-和 H-的形成，而后者则导致 H2 的形成。FA 碎片产物的身份、产率和分支比与气相有很大不同，并且取决于辐射类型、冰结构以及 SiO2 纳米颗粒的存在。后者可能会增加离子-电子复合和自由基复合的速率。观察到的主要产物表明，与气相离解相比，凝聚相离解通道有很大的不同。在 Lyman-α光解或电子辐照下，FA 形成离子/产物的情况不容忽视，这两种过程都可能在星际区域以及土卫六的大气层中处理冰。
