Nuclear spin blockade of laser ignition of intramolecular rotation in the model boron rotor 11B13+
Nuclear spin blockade of laser ignition of intramolecular rotation in the model boron rotor 11B13+
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模型硼转子11B13中分子内旋转激光点火的核自旋封锁
DOI：
10.1063/1.5048358
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发表时间：
2018-11-14
影响因子：
4.4
通讯作者：
Yang, Yonggang
中科院分区：
文献类型：
--
作者：
Grohmann, Thomas;Haase, Dietrich;Yang, Yonggang
硼转子B-11(13)+由一个三原子内“轮”组成，该轮可以在其伪旋转的十原子外“轴承”中旋转——这种协调运动称为“扭转”。 B-11(13)+ 在其基态下具有零扭转角动量。从这个初始状态开始，通过激光脉冲引发扭曲是一个挑战。然而，我们发现这是不可能的，即无法设计任何激光脉冲来诱导具有非零扭转角动量从基态到激发态的跃迁。原因是基态的特征是其扭曲波函数和核自旋波函数的不可约表示（IRREP）的特定组合。激光脉冲保存了这些 IRREP，因为 IRREP 的假设变化需要核自旋翻转，而这在与激光脉冲相互作用期间无法实现。我们证明，具有非零扭转角动量的 B-11(13)+ 的所有激发目标态都具有激光脉冲无法访问的不同 IRREP。因此，核自旋守恒阻止了激光诱导的从非旋转基态到旋转目标态的转变。我们发现核自旋守恒所施加的各种额外限制，例如，激光脉冲可以顺时针改变为逆时针扭曲，反之亦然，但它们无法阻止它们。结果是在简单模型的框架中得出的。由 AIP 出版社出版。
The boron rotor B-11(13)+ consists of a tri-atomic inner "wheel" that may rotate in its pseudo-rotating ten-atomic outer "bearing"-this concerted motion is called "contorsion." B-11(13)+ in its ground state has zero contorsional angular momentum. Starting from this initial state, it is a challenge to ignite contorsion by a laser pulse. We discover, however, that this is impossible, i.e., one cannot design any laser pulse that induces a transition from the ground to excited states with non-zero contorsional angular momentum. The reason is that the ground state is characterized by a specific combination of irreducible representations (IRREPs) of its contorsional and nuclear spin wavefunctions. Laser pulses conserve these IRREPs because hypothetical changes of the IRREPs would require nuclear spin flips that cannot be realized during the interaction with the laser pulse. We show that all excited target states of B-11(13)+ with non-zero contorsional angular momentum have different IRREPs that are inaccessible by laser pulses. Conservation of nuclear spins thus prohibits laser-induced transitions from the non-rotating ground to rotating target states. We discover various additional constraints imposed by conservation of nuclear spins, e.g., laser pulses can change clockwise to counter-clockwise contorsions or vice versa, but they cannot stop them. The results are derived in the frame of a simple model. Published by AIP Publishing.