Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
Phys Chem Chem Phys. 2019 Mar 13;21(11):6247-6255. doi: 10.1039/c8cp07474g.
The diffusional dynamics of atomic oxygen in and on amorphous solid water (ASW) to form molecular oxygen is characterized. Reactive molecular dynamics simulations to study bond breaking and bond formation show that vibrational relaxation of the highly excited diatomic occurs on the 10 ns to 100 ns time scale. The relaxation process is highly nonexponential and can be characterized by a stretched exponential decay reminiscent of the dynamics of glasses. The stretched exponents range from β = 0.15 for relaxation on the surface to β = 0.21 for the dynamics in bulk. It is also found that coupling of the O2 relaxation to the internal water modes occurs which speeds up the vibrational relaxation by a factor of 4. Extrapolation of the stretched exponential decay to 1 μs yields a final vibrational quantum number v = 2 for O2(X3Σ-g), consistent with experimental results from photolysis of SO2 on ASW at 193 nm which find v ≤ 3. Desorption energies of water from the surface range from 1.5 to 2.0 kcal mol-1 compared with 1.8 kcal mol-1 found from experiment, depending on whether the water molecules are flexible or not.
研究了原子氧在非晶态水（ASW）中及表面的扩散动力学，以形成分子氧。反应分子动力学模拟研究表明，高度激发的双原子的振动弛豫发生在 10 ns 到 100 ns 的时间尺度内。弛豫过程高度非指数，可用类似于玻璃动力学的拉伸指数衰减来描述。拉伸指数的范围从表面上的 β = 0.15 到体相中的 β = 0.21。还发现，O2 弛豫与内部水分子模式的耦合会加速振动弛豫，使其速度提高 4 倍。将拉伸指数衰减外推到 1 μs，得到 O2（X3Σ-g）的最终振动量子数 v = 2，与在 193nm 处用 ASW 光解 SO2 的实验结果一致，实验结果发现 v ≤ 3。与实验值 1.8 kcal mol-1 相比，表面上水的脱附能范围为 1.5 到 2.0 kcal mol-1，具体取决于水分子是否灵活。
