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Photolytic mechanisms of hydroxylamine

机译：羟胺的光解机制

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摘要

The photodissociation of small molecules has been extensively studied because of the increase in environmental problems related to the atmosphere of the Earth. In this work, the photodissociation mechanisms of hydroxylamine (NH2OH) as a model molecule in its lowest singlet-excited (S-1) state were systematically studied using the complete active space second-order perturbation theory (CASPT2) and transition state theory (TST). In particular, this study focused on nonradiative relaxation processes that convert the S-0 -> S-1 excited-state molecule to its products in their respective electronic ground states. The potential energy curves obtained from relaxed scans suggest that O-H dissociation is the preferred process in the S-1 state. For the N-O and N-H dissociation pathways, thermally excited precursors were hypothesized to form in the S-0 state to circumvent O-H dissociation. Thus, S-0 -> S-1 vertical excitations lead to transition structures in the S-1 state, which fragment to their respective electronic-ground-state products. The thermodynamic and kinetic results confirmed the precursor hypothesis, showing that the exothermic energy caused by the formation of HNO and H-2 is sufficient to generate such precursors in the S-0 state. Additionally, the TST confirmed that unimolecular isomerization-dissociation is a two-step process that generates products effectively by direct photolysis of the corresponding covalent bonds. In particular, the process consists of O-H bond dissociation, followed by spontaneous isomerization and formation of H-2 in its electronic ground state, resulting in the high quantum yield observed in the UV absorption experiments in the preferential formation of HNO and H-2. The configuration interaction coefficients of the characteristic structures on the potential energy curves revealed considerable changes in the multiconfigurational character of the wavefunctions, especially for the transition structures. These are characterized by the development of Rydberg orbitals, being produced at the intersection of the S-0 and S-1 states. The present study highlights the effects of thermal selectivity and the multiconfigurational character of the wavefunctions on photodissociation. Because detailed information on the photolytic mechanisms of isolated NH2OH is limited both theoretically and experimentally, these results provide fundamental insight into unimolecular photodissociation, posing ground for future studies on related systems.
机译：由于与地球气氛有关的环境问题的增加，小分子的光解离已经过广泛研究。在这项工作中，系统地使用完整的主动空间二阶扰动理论（Caspt2）和过渡状态理论（TST）系统地研究了羟胺（NH 2 OH）作为模型分子作为模型分子的光度分子作为模型分子的光解码机制。（TST ）。特别地，该研究的重点是在其各自的电子地位中将S-0-> S-1激发状态分子转化为其产物的非散弛弛豫方法。从弛豫扫描获得的潜在能量曲线表明O-H离解是S-1状态中的优选方法。对于N-O和N-H解离途径，假设热激发前体以在S-0状态下形成，以绕过O-H离解。因此，S-0 - > S-1垂直激励导致S-1状态下的过渡结构，其分段到它们各自的电子地态产品。热力学和动力学结果证实了前体假设，表明由HNO和H-2形成引起的放热能量足以在S-0状态下产生这种前体。另外，TST证实了单分子异构化 - 解离是一种两步方法，其通过直接光解相应的共价键有效地产生产品。特别地，该方法由O-H键解离解剖，然后在其电子地面状态下自发异构化和形成H-2，从而在优先形成HNO和H-2中观察到的高量子产率。潜在能量曲线上的特征结构的配置交互系数揭示了波力的多功能性特性的显着变化，特别是对于过渡结构。这些以rydberg轨道的发展为特征，在S-0和S-1状态的交叉处产生。本研究突出了热选择性的影响和波力切断对光度切断的影响。因为关于隔离NH 2OH的光解机制的详细信息理论上和实验，所以这些结果对单分子的光化，构成了对相关系统的未来研究的基础知识提供了基础的洞察力。

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  • 来源
    《RSC Advances》 |2020年第14期|共13页
  • 作者

    Thisuwan Jittima; Promma Phorntep; Sagarik Kritsana;

  • 作者单位

    Nakhon Phanom Univ Fac Educ Div Sci Nakhon Phanom 48000 Thailand;

    Suranaree Univ Technol Inst Sci Sch Chem Nakhan Ratchasima 30000 Thailand;

    Suranaree Univ Technol Inst Sci Sch Chem Nakhan Ratchasima 30000 Thailand;

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  • 正文语种 eng
  • 中图分类 化学;
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