Balabanoff Morgan E, Ruzi Mahmut, Anderson David T
Department of Chemistry, University of Wyoming, Laramie, WY 82071, USA.
Phys Chem Chem Phys. 2017 Dec 20;20(1):422-434. doi: 10.1039/c7cp05064j.
We are studying the details of hydrogen atom (H atom) quantum diffusion in highly enriched parahydrogen (pH) quantum solids doped with chemical species in an effort to better understand H atom transport and reactivity under these conditions. In this work we present kinetic studies of the 193 nm photo-induced chemistry of methanol (CHOH) isolated in solid pH. Short-term irradiation of CHOH at 1.8 K readily produces CHO and CO which we detect using FTIR spectroscopy. The in situ photochemistry also produces CHO and H atoms which we can infer from the post-photolysis reaction kinetics that display significant CHOH growth. The CHOH growth kinetics indicate at least three separate tunneling reactions contribute; (i) reactions of photoproduced CHO with the pH host, (ii) H atom reactions with the CHO photofragment, and (iii) long-range migration of H atoms and reaction with CHOH. We assign the rapid CHOH growth to the following CHO + H → CHOH + H → CHOH + H two-step sequential tunneling mechanism by conducting analogous kinetic measurements using deuterated methanol (CDOD). By performing photolysis experiments at 1.8 and 4.3 K, we show the post-photolysis reaction kinetics change qualitatively over this small temperature range. We use this qualitative change in the reaction kinetics with temperature to identify reactions that are quantum diffusion limited. While these results are specific to the conditions that exist in pH quantum solids, they have direct implications on the analogous low temperature H atom tunneling reactions that occur on metal surfaces and on interstellar grains.
我们正在研究在掺杂化学物种的高浓缩仲氢（pH）量子固体中氢原子（H原子）的量子扩散细节，以便更好地理解这些条件下H原子的传输和反应活性。在这项工作中，我们展示了对固态pH中分离出的甲醇（CH₃OH）的193nm光诱导化学的动力学研究。在1.8K下对CH₃OH进行短期辐照很容易产生CHO和CO，我们使用傅里叶变换红外光谱法进行检测。原位光化学还产生了CHO和H原子，我们可以从光解后反应动力学推断出这一点，该动力学显示出CH₃OH有显著增长。CH₃OH的增长动力学表明至少有三个独立的隧穿反应起作用：（i）光产生的CHO与pH主体的反应，（ii）H原子与CHO光碎片的反应，以及（iii）H原子的长程迁移和与CH₃OH的反应。通过使用氘代甲醇（CD₃OD）进行类似的动力学测量，我们将CH₃OH的快速增长归因于以下CHO + H → CHOH + H → CHOH + H两步连续隧穿机制。通过在1.8K和4.3K下进行光解实验，我们表明在这个小温度范围内光解后反应动力学发生了定性变化。我们利用反应动力学随温度的这种定性变化来识别受量子扩散限制的反应。虽然这些结果特定于pH量子固体中存在的条件，但它们对在金属表面和星际尘埃上发生的类似低温H原子隧穿反应有直接影响。
