Sandia National Laboratories, Livermore, 94550, CA, USA.
Applied Materials, Inc., Santa Clara, 95051, CA, USA.
Nat Commun. 2023 Jun 3;14(1):3227. doi: 10.1038/s41467-023-38873-z.
Optical centrifuges are laser-based molecular traps that can rotationally accelerate molecules to energies rivalling or exceeding molecular bond energies. Here we report time and frequency-resolved ultrafast coherent Raman measurements of optically centrifuged CO at 380 Torr spun to energies beyond its bond dissociation energy of 5.5 eV (J = 364, E = 6.14 eV, E/k = 71, 200 K). The entire rotational ladder from J = 24 to J = 364 was resolved simultaneously which enabled a more accurate measurement of the centrifugal distortion constants for CO. Remarkably, coherence transfer was directly observed, and time-resolved, during the field-free relaxation of the trap as rotational energy flowed into bending-mode vibrational excitation. Vibrationally excited CO (ν > 3) was observed in the time-resolved spectra to populate after 3 mean collision times as a result of rotational-to-vibrational (R-V) energy transfer. Trajectory simulations show an optimal range of J for R-V energy transfer. Dephasing rates for molecules rotating up to 5.5 times during one collision were quantified. Very slow decays of the vibrational hot band rotational coherences suggest that they are sustained by coherence transfer and line mixing.
光学离心机是基于激光的分子陷阱，可以将分子旋转加速到与分子键能相当或超过的能量。在这里，我们报告了在 380 托的 CO 进行光学离心旋转，能量超过其 5.5 eV 的键解离能（J = 364，E = 6.14 eV，E/k = 71,200 K）时的时间和频率分辨超快相干拉曼测量。整个从 J = 24 到 J = 364 的旋转梯级同时得到了分辨，这使得对 CO 的离心畸变常数进行了更准确的测量。值得注意的是，在阱的场自由弛豫期间，直接观察到了相干转移，并进行了时间分辨，因为旋转能流入弯曲模式振动激发。在时间分辨光谱中观察到振动激发的 CO（ν > 3），在 3 个平均碰撞时间后作为旋转到振动（R-V）能量转移的结果而被激发。轨迹模拟表明了 R-V 能量转移的最佳 J 范围。旋转分子在一次碰撞中旋转 5.5 倍以上的退相率进行了量化。振动热带旋转相干的非常缓慢衰减表明它们是由相干转移和谱线混合维持的。
