Communication: On the competition between adiabatic and nonadiabatic dynamics in vibrationally mediated ammonia photodissociation in its A band.
Communication: On the competition between adiabatic and nonadiabatic dynamics in vibrationally mediated ammonia photodissociation in its A band.
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DOI：
10.1063/1.4913633
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
Changjian Xie;Xiaolei Zhu;Jianyi Ma;D. Yarkony;D. Xie;Hua Guo
中科院分区：
文献类型：
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作者：
Changjian Xie;Xiaolei Zhu;Jianyi Ma;D. Yarkony;D. Xie;Hua Guo
非绝热过程在光化学中起着重要的作用，但电子能量转化为化学能的机制尚不清楚。为了探索在一个典型的光反应中非绝热动力学振动控制的可能性，即NH_3(X̃(1)Al)的A带光解，在最近发展起来的耦合非绝热势能面上研究了对称或反对称伸缩激发NH_3(X̃(1)Al)的全维态到态量子动力学。重现了实验观察到的H原子动能分布。然而，与以往的推论相反，无论NH3(X̃(1)A1)的初始制备如何，NH2(Au2)A1/NH2(X̃(2)B1)的支化比都很小，而主要碎片NH2(X̃(2)B1)的内态分布强烈依赖于NH3(X̃(1)A1)的初始振动激发。由反对称伸缩基态引起的慢H原子光解是由于内激NH_2(X̃(2)B_1)碎片中的能量隔离，而不是先前提出的NH_2(？)(2)A_1中的能量。NH_2(X̃(2)B_1)碎片的高内激发归因于分子通过锥形交叉缝隙到达NH_3基电子态时所受到的力矩。因此，在这个系统中，与以前的断言相反，通过选择激发基态振动模式来控制电子态分支是无效的。精确的量子力学结果与基于准经典表面跳跃轨迹的互补结果并列在一起，为非绝热过程提供了重要的见解。
Non-adiabatic processes play an important role in photochemistry, but the mechanism for conversion of electronic energy to chemical energy is still poorly understood. To explore the possibility of vibrational control of non-adiabatic dynamics in a prototypical photoreaction, namely, the A-band photodissociation of NH3(X̃(1)A1), full-dimensional state-to-state quantum dynamics of symmetric or antisymmetric stretch excited NH3(X̃(1)A1) is investigated on recently developed coupled diabatic potential energy surfaces. The experimentally observed H atom kinetic energy distributions are reproduced. However, contrary to previous inferences, the NH2(Ã(2)A1)/NH2(X̃(2)B1) branching ratio is found to be small regardless of the initial preparation of NH3(X̃(1)A1), while the internal state distribution of the preeminent fragment, NH2(X̃(2)B1), is found to depend strongly on the initial vibrational excitation of NH3(X̃(1)A1). The slow H atoms in photodissociation mediated by the antisymmetric stretch fundamental state are due to energy sequestered in the internally excited NH2(X̃(2)B1) fragment, rather than in NH2(Ã(2)A1) as previously proposed. The high internal excitation of the NH2(X̃(2)B1) fragment is attributed to the torques exerted on the molecule as it passes through the conical intersection seam to the ground electronic state of NH3. Thus in this system, contrary to previous assertions, the control of electronic state branching by selective excitation of ground state vibrational modes is concluded to be ineffective. The juxtaposition of precise quantum mechanical results with complementary results based on quasi-classical surface hopping trajectories provides significant insights into the non-adiabatic process.