Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI 96822, USA.
Phys Chem Chem Phys. 2011 May 28;13(20):9469-82. doi: 10.1039/c1cp20434c. Epub 2011 Apr 11.
The irradiation of pure molecular oxygen (O(2)) and carbon dioxide (CO(2)) ices with 5 keV H(+) and He(+) ions was investigated experimentally to simulate the chemical processing of oxygen rich planetary and interstellar surfaces by exposure to galactic cosmic ray (GCR), solar wind, and magnetospheric particles. Deposited at 12 K under ultra-high vacuum conditions (UHV), the irradiated condensates were monitored on-line and in situ in the solid-state by Fourier transform infrared spectroscopy (FTIR), revealing the formation of ozone (O(3)) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO(3)) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H(2)), atomic helium (He) and molecular oxygen (O(2)) were identified in the subliming oxygen and carbon dioxide condensates by quadrupole mass spectrometry (QMS). Temporal abundances of the oxygen and carbon dioxide precursors and the observed molecular products were compiled over the irradiation period to develop reaction schemes unfolding in the ices. These reactions were observed to be dependent on the generation of atomic oxygen (O) by the homolytic dissociation of molecular oxygen induced by electronic, S(e), and nuclear, S(n), interaction with the impinging ions. In addition, the destruction of the ozone and carbon trioxide products back to the molecular oxygen and carbon dioxide precursors was promoted over an extended period of ion bombardment. Finally, destruction and formation yields were calculated and compared between irradiation sources (including 5 keV electrons) which showed a surprising correlation between the molecular yields (∼10(-3)-10(-4) molecules eV(-1)) created by H(+) and He(+) impacts. However, energy transfer by isoenergetic, fast electrons typically generated ten times more product molecules per electron volt (∼10(-2)-10(-3) molecules eV(-1)) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.
用 5 keV 的 H(+)和 He(+)离子辐照纯的分子氧（O(2)）和二氧化碳（CO(2)）冰，以模拟富含氧的行星和星际表面在暴露于银河宇宙射线（GCR）、太阳风和磁层粒子时的化学处理过程。在 12 K 下，在超高真空条件（UHV）下沉积，辐照后的凝结核在固态下进行在线和原位监测，通过傅里叶变换红外光谱（FTIR），在辐照氧冰中发现了臭氧（O(3)）的形成；在辐照二氧化碳中发现了臭氧、一氧化碳（CO）和环状碳酸三酯（c-CO(3)）。除了这些辐照产物外，在升华的氧和二氧化碳凝结核中，通过四极质谱（QMS）还鉴定出气相分子氢（H(2)）、原子氦（He）和分子氧（O(2)）的演化。在辐照期间，编译了氧和二氧化碳前体的时间丰度和观察到的分子产物，以开发在冰中展开的反应方案。这些反应被观察到依赖于由电子、S(e)和核、S(n)与撞击离子的均裂解离诱导的分子氧的原子氧（O）的生成。此外，在离子轰击的延长时间内，促进了臭氧和碳酸三酯产物的破坏和形成回分子氧和二氧化碳前体。最后，计算并比较了不同辐照源（包括 5 keV 电子）之间的破坏和形成产率，结果表明 H(+)和 He(+)撞击产生的分子产率（约 10(-3)-10(-4)个分子 eV(-1)）之间存在惊人的相关性。然而，具有相同能量的快速电子的能量转移通常比暴露于离子时每电子伏特产生的产物分子多十倍（约 10(-2)-10(-3)个分子 eV(-1)）。还讨论了这些发现对太阳系化学的影响。
