Nuclear Spin Relaxation in Cold Atom–Molecule Collisions
Nuclear Spin Relaxation in Cold Atom–Molecule Collisions
复制标题
冷原子分子碰撞中的核自旋弛豫
DOI：
10.1021/acs.jpca.2c08646
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Tscherbul, Timur V.
中科院分区：
文献类型：
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作者：
Hermsmeier, Rebekah;Xing, Xiaodong;Tscherbul, Timur V.
我们研究了在外磁场中与无结构原子冷碰撞of1Σ+分子中核自旋弛豫的量子动力学。为此，我们开发了一种严格的耦合通道方法，该方法考虑了旋转和核自旋自由度of1Σ+分子及其与外部磁场的相互作用以及各向异性原子-分子相互作用。我们应用该方法研究了13co分子在4he原子冷缓冲气体中的核自旋亚能级的碰撞弛豫。我们发现在13co的地面旋转流形（N= 0）中，由于核自旋亚能级之间没有直接耦合，核自旋弛豫发生得非常缓慢。13co的旋转激发（N= 1）核自旋态之间的碰撞跃迁速率通常要高得多，这是由于态之间的直接核自旋-旋转耦合。这些跃迁服从选择规则，这取决于初始和最终分子状态的旋转和核自旋角动量（MNandMI）的空间固定投影值。对于某些初始状态，我们还观察到强磁场依赖，这可以通过使用第一个玻恩近似来理解。我们利用计算出的核自旋弛豫速率研究了13co （N= 0）在4he冷缓冲气体中的单核自旋态的热化。当He密度为10 ~ 14cm - 3时，核自旋弛豫时间（T1≤1 s atT= 1 K）随温度升高而急剧下降，这是由于旋转激发态数量的增加导致核自旋弛豫速率大大加快。因此，在与缓冲气体原子的冷碰撞中，只有在足够低的温度下（kBT≪2Be）才能维持n = 0的核自旋态的长松弛时间，其中bea是旋转常数。
We explore the quantum dynamics of nuclear spin relaxation in cold collisions of1Σ+molecules with structureless atoms in an external magnetic field. To this end, we develop a rigorous coupled-channel methodology, which accounts for rotational and nuclear spin degrees of freedom of1Σ+molecules and their interaction with an external magnetic field as well as anisotropic atom–molecule interactions. We apply the methodology to study the collisional relaxation of the nuclear spin sublevels of13CO molecules immersed in a cold buffer gas of4He atoms. We find that nuclear spin relaxation in the ground rotational manifold (N= 0) of13CO occurs extremely slowly due to the absence of direct couplings between the nuclear spin sublevels. The rates of collisional transitions between the rotationally excited (N= 1) nuclear spin states of13CO are generally much higher due to the direct nuclear spin–rotation coupling between the states. These transitions obey selection rules, which depend on the values of space-fixed projections of rotational and nuclear spin angular momenta (MNandMI) for the initial and final molecular states. For some initial states, we also observe a strong magnetic field dependence, which can be understood by using the first Born approximation. We use our calculated nuclear spin relaxation rates to investigate the thermalization of a single nuclear spin state of13CO(N= 0) immersed in a cold buffer gas of4He. The calculated nuclear spin relaxation times (T1≃ 1 s atT= 1 K at a He density of 10–14cm–3) display a steep temperature dependence decreasing rapidly at elevated temperatures due to the increased population of rotationally excited states, which undergo nuclear spin relaxation at a much faster rate. Thus, long relaxation times ofN= 0 nuclear spin states in cold collisions with buffer gas atoms can be maintained only at sufficiently low temperatures (kBT≪ 2Be), whereBeis the rotational constant.