Murray Matthew J, Ogden Hannah M, Toro Carlos, Liu Qingnan, Burns David A, Alexander Millard H, Mullin Amy S
Department of Chemistry and Biochemistry, University of Maryland , College Park, Maryland 20742, United States.
J Phys Chem A. 2015 Dec 17;119(50):12471-9. doi: 10.1021/acs.jpca.5b07941. Epub 2015 Oct 26.
An optical centrifuge pulse drives carbon dioxide molecules into ultrahigh rotational states with rotational frequencies of ω ≈ 32 THz based on the centrifuge frequency at the full width at half-maximum of the spectral chirp. High-resolution transient IR absorption spectroscopy is used to measure the time-evolution of translational and rotational energy for a number of states in the range of J = 0-100 at a sample pressure of 5-10 Torr. Transient Doppler profiles show that the products of super rotor collisions contain substantial amounts of translational energy, with J-dependent energies correlating to a range of ΔJ propensities. The transient population in J = 100 is short-lived, indicating rapid relaxation of high J states; populations in J = 36, 54, and 76 increase overall as the super rotor energy is redistributed. Transient line profiles for J = 0 and 36 are consistently narrower than the initial ambient sample temperature, showing that collision cross sections for super rotors increase with decreasing collision energy. Quantum scattering calculations on Ar-CO2(j) collisions are used to interpret the qualitative features of the experimental results. The results of this study provide the groundwork for developing a more complete understanding of super rotor dynamics.
基于光谱啁啾半高宽处的离心机频率，光学离心机脉冲将二氧化碳分子驱动到旋转频率ω≈32太赫兹的超高旋转态。在5 - 10托的样品压力下，利用高分辨率瞬态红外吸收光谱法测量J = 0 - 100范围内多个态的平动和转动能量随时间的演化。瞬态多普勒轮廓表明，超转子碰撞产物包含大量平动能，与一系列ΔJ倾向相关的J依赖能量。J = 100时的瞬态布居寿命短暂，表明高J态快速弛豫；随着超转子能量重新分布，J = 36、54和76时的布居总体增加。J = 0和36的瞬态谱线轮廓始终比初始环境样品温度窄，表明超转子的碰撞截面随碰撞能量降低而增加。对Ar-CO2(j)碰撞进行的量子散射计算用于解释实验结果的定性特征。本研究结果为更全面理解超转子动力学奠定了基础。
