范德华和氢键簇阳离子的动力学和碎片化：（NH3）n和（NH3BH3）n在10.51 eV电离,The Journal of Chemical Physics

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范德华和氢键簇阳离子的动力学和碎片化：（NH3）n和（NH3BH3）n在10.51 eV电离
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2016-04-14 15:03:39 , DOI: 10.1063/1.4945624
Bing Yuan ₁ , Joong-Won Shin ₂ , Elliot R. Bernstein ₁

Affiliation

118 nm激光器用作高能量单光子（10.51 eV /光子）源，用于通过飞行时间质谱研究氨硼烷（NH ₃ BH ₃）阳离子及其簇离子的动力学和裂解。为了说明氨硼烷的结果，还在相同条件下研究了氨离子及其簇离子的行为。（NH ₃ BH ₃）_n及其阳离子的电荷分布，分子轨道和自旋密度在二阶扰动理论（MP2）和完全活动空间自洽场（CASSCF）理论水平上均得到了研究。NH ₃ BH离子化的初始解离机理和势能面₃，NH ₃及其簇以MP2 / 6-311 ++ G（d，p）水平计算。质子团（NH ₃）_x H ⁺占主导地位的氨团簇质谱：我们的计算表明，新生的（NH ₃）_n⁺形成的（NH ₃）_n-1 H ⁺和NH ₂对系统的能垒最低。发现在这些条件下（NH ₃）_n⁺和（NH ₃ BH ₃）_n⁺质谱的唯一共同特征是NH _y⁺（y = 0，…，4）在m / z = 14–18处。观察到同时具有¹¹ B和¹⁰ B同位素的分子离子，因此，对于（NH ₃ BH ₃）_n簇系统观察到的产物离子本身源自（NH ₃ BH ₃）_n簇，而不是源自NH的NH ₃部分₃ BH ₃单。NH ₃ BH ₂⁺是（NH ₃ BH ₃）_n^+中最丰富的电离产物团簇谱：计算结果表明，对于NH ₃ BH ₃⁺，H原子从BH ₃部分损失，能量垒为0.67 eV。为（NH ₃ BH ₃）₂⁺和（NH ₃ BH ₃）₃⁺集群，一个乙^δ+ ⋯ħ ^δ- ⋯ ^δ-ħ⋯ ^δ+乙键可形成在相应的簇离子，从而产生较低的能量，更稳定的离子结构。（NH ₃ BH ₃）_n⁺（n = 2，3）解离的第一步是打破B^δ+ ⋯ħ ^δ- ⋯ ^δ-ħ⋯ ^δ+乙部分，导致H的随后释放₂从后者团簇离子。使用各种簇和单体的价电子分布的CASSCF自然键轨道描述，可以最好地表示和理解所计算的总体反应机理。将本结果与对于固体NH ₃ BH ₃所发现的结果进行比较表明，NH ₃ BH ₃可以是良好的储氢材料。

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Dynamics and fragmentation of van der Waals and hydrogen bonded cluster cations: (NH3)n and (NH3BH3)n ionized at 10.51 eV

A 118 nm laser is employed as a high energy, single photon (10.51 eV/photon) source for study of the dynamics and fragmentation of the ammonia borane (NH₃BH₃) cation and its cluster ions through time of flight mass spectrometry. The behavior of ammonia ion and its cluster ions is also investigated under identical conditions in order to explicate the ammonia borane results. Charge distributions, molecular orbitals, and spin densities for (NH₃BH₃)_n and its cations are explored at both the second-order perturbation theory (MP2) and complete active space self-consistent field (CASSCF) theory levels. Initial dissociation mechanisms and potential energy surfaces for ionized NH₃BH₃, NH₃, and their clusters are calculated at the MP2/6-311++G(d,p) level. Protonated clusters (NH₃)_xH⁺ dominate ammonia cluster mass spectra: our calculations show that formation of (NH₃)_n−1H⁺ and NH₂ from the nascent (NH₃)_n⁺ has the lowest energy barrier for the system. The only common features for the (NH₃)_n⁺ and (NH₃BH₃)_n⁺mass spectra under these conditions are found to be NH_y⁺ (y = 0,…,4) at m/z = 14–18. Molecular ions with both ¹¹B and ¹⁰B isotopes are observed, and therefore, product ions observed for the (NH₃BH₃)_n cluster system derive from (NH₃BH₃)_n clusters themselves, not from the NH₃ moiety of NH₃BH₃ alone. NH₃BH₂⁺ is the most abundant ionization product in the (NH₃BH₃)_n⁺ cluster spectra: calculations support that for NH₃BH₃⁺, an H atom is lost from the BH₃ moiety with an energy barrier of 0.67 eV. For (NH₃BH₃)₂⁺ and (NH₃BH₃)₃⁺ clusters, a B^δ+⋯H^δ−⋯^δ−H⋯^δ+B bond can form in the respective cluster ions, generating a lower energy, more stable ion structure. The first step in the (NH₃BH₃)_n⁺ (n = 2, 3) dissociation is the breaking of the B^δ+⋯H^δ−⋯^δ−H⋯^δ+B moiety, leading to the subsequent release of H₂ from the latter cluster ion. The overall reaction mechanisms calculated are best represented and understood employing a CASSCF natural bond orbital description of the valence electron distribution for the various clusters and monomers. Comparison of the present results with those found for solid NH₃BH₃ suggests that NH₃BH₃ can be a good hydrogen storage material.

更新日期：2016-04-15

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