Yuan Bing, Bernstein Elliot R
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA.
J Chem Phys. 2017 Jan 7;146(1):014301. doi: 10.1063/1.4972259.
Unimolecular decomposition of energetic molecules, 3,3'-diamino-4,4'-bisfuroxan (labeled as A) and 4,4'-diamino-3,3'-bisfuroxan (labeled as B), has been explored via 226/236 nm single photon laser excitation/decomposition. These two energetic molecules, subsequent to UV excitation, create NO as an initial decomposition product at the nanosecond excitation energies (5.0-5.5 eV) with warm vibrational temperature (1170 ± 50 K for A, 1400 ± 50 K for B) and cold rotational temperature (<55 K). Initial decomposition mechanisms for these two electronically excited, isolated molecules are explored at the complete active space self-consistent field (CASSCF(12,12)/6-31G(d)) level with and without MP2 correction. Potential energy surface calculations illustrate that conical intersections play an essential role in the calculated decomposition mechanisms. Based on experimental observations and theoretical calculations, NO product is released through opening of the furoxan ring: ring opening can occur either on the S excited or S ground electronic state. The reaction path with the lowest energetic barrier is that for which the furoxan ring opens on the S state via the breaking of the N1-O1 bond. Subsequently, the molecule moves to the ground S state through related ring-opening conical intersections, and an NO product is formed on the ground state surface with little rotational excitation at the last NO dissociation step. For the ground state ring opening decomposition mechanism, the N-O bond and C-N bond break together in order to generate dissociated NO. With the MP2 correction for the CASSCF(12,12) surface, the potential energies of molecules with dissociated NO product are in the range from 2.04 to 3.14 eV, close to the theoretical result for the density functional theory (B3LYP) and MP2 methods. The CASMP2(12,12) corrected approach is essential in order to obtain a reasonable potential energy surface that corresponds to the observed decomposition behavior of these molecules. Apparently, highly excited states are essential for an accurate representation of the kinetics and dynamics of excited state decomposition of both of these bisfuroxan energetic molecules. The experimental vibrational temperatures of NO products of A and B are about 800-1000 K lower than previously studied energetic molecules with NO as a decomposition product.
通过226/236 nm单光子激光激发/分解，研究了含能分子3,3'-二氨基-4,4'-双呋咱（标记为A）和4,4'-二氨基-3,3'-双呋咱（标记为B）的单分子分解。这两种含能分子在紫外激发后，在纳秒激发能量（5.0 - 5.5 eV）下产生NO作为初始分解产物，具有温热的振动温度（A为1170 ± 50 K，B为1400 ± 50 K）和低温的转动温度（<55 K）。在有和没有MP2校正的完全活性空间自洽场（CASSCF(12,12)/6 - 31G(d)）水平上，探索了这两种电子激发的孤立分子的初始分解机制。势能面计算表明，锥形交叉在计算的分解机制中起着至关重要的作用。基于实验观察和理论计算，NO产物通过呋咱环的打开释放：环打开可以发生在单重激发态或单重基态。能量势垒最低的反应路径是呋咱环通过N1 - O1键的断裂在单重激发态打开。随后，分子通过相关的开环锥形交叉移动到基态，并且在最后NO解离步骤中在基态表面形成几乎没有转动激发的NO产物。对于基态开环分解机制，N - O键和C - N键一起断裂以生成解离的NO。对CASSCF(12,12)表面进行MP2校正后，具有解离NO产物的分子的势能范围为2.04至3.14 eV，接近密度泛函理论（B3LYP）和MP2方法的理论结果。为了获得与这些分子观察到的分解行为相对应的合理势能面，CASMP2(12,12)校正方法至关重要。显然，高激发态对于准确描述这两种双呋咱含能分子激发态分解的动力学和动力学至关重要。A和B的NO产物的实验振动温度比先前研究的以NO作为分解产物的含能分子低约800 - 1000 K。
