Title: Femtosecond Symmetry Breaking and Coherent Relaxation of Methane Cations at the Carbon K-Edge Show Chinese title

Title: 飞秒碳K边甲烷阳离子的对称性破缺与相干弛豫

Abstract: Understanding the relaxation pathways of photoexcited molecules is essential to gain atomistic level insight into photochemistry. Herein, we perform a time-resolved study of ultrafast molecular symmetry breaking via geometric relaxation (Jahn-Teller distortion) on the methane cation. Attosecond transient absorption spectroscopy with soft X-rays at the carbon K-edge reveals that the distortion occurs within $10\pm 2$ femtoseconds after few-femtosecond strong-field ionization of methane. The distortion activates coherent oscillations in the scissoring vibrational mode of the symmetry broken cation, which are detected in the X-ray signal. These oscillations are damped within $58\pm13$ femtoseconds, as vibrational coherence is lost with the energy redistributing into lower-frequency vibrational modes. This study completely reconstructs the molecular relaxation dynamics of this prototypical example and opens new avenues for exploring complex systems. Show Chinese abstract

Abstract: 理解光激发分子的弛豫路径对于获得光化学的原子级见解至关重要。 在此，我们对甲烷阳离子在碳K边的软X射线阿秒瞬态吸收光谱中通过几何弛豫（Jahn-Teller畸变）进行超快分子对称性破缺的时间分辨研究。 在甲烷的少飞秒强场电离后，碳K边的软X射线阿秒瞬态吸收光谱显示，畸变发生在$10\pm 2$飞秒内。 该畸变激活了对称性破缺阳离子的剪切振动模式中的相干振荡，并在X射线信号中被检测到。 这些振荡在$58\pm13$飞秒内被阻尼，因为振动相干性随着能量重新分布到低频振动模式而丧失。 本研究完全重建了这一典型例子的分子弛豫动力学，并为探索复杂系统开辟了新途径。