10月20日 Shaul Mukamel:Probing elementary molecular events by ultrafast spectroscopy with coherent and noisy X ray pulses(院士报告)(69周年校庆系列学术报告)

来源:pt真人平台 时间:2020-10-12浏览:10设置


讲座题目:Probing elementary molecular events by ultrafast  spectroscopy with coherent and noisy X ray pulses

主讲人:Shaul Mukamel  院士

主持人:康司坦丁 教授

开始来源:pt真人平台 时间:2020-10-20 14:00:00

讲座地址:腾讯会议   ID919 256 643

主办单位:精密光谱科学与技术国家重点实验室

 

报告人简介:

B. Sc. - Tel-Aviv University, 1969, cum laude; M. Sc. - Tel-Aviv University,   1971, summa cum laude;

Ph.D.  - Tel-Aviv University, 1976, summa cum laude

July 2013-present: Distinguished Professor of   Chemistry, University of California at Irvine; 2003-June 2013: Chancellor   Professor of Chemistry, University of California at Irvine;  2002-2003:Professor of Physics and   Astronomy, University of Rochester, Rochester, New York;  2000-2003:C. E. Kenneth Mees Professor of Chemistry,   University of Rochester, Rochester, New York; 1985-2000: Professor,   Department of Chemistry, University of Rochester, Rochester, New York;   1982-85: Associate Professor, Department of Chemistry, University of   Rochester, Rochester, New York

 

报告内容:

Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity  of core X-ray excitations offer a uniquely high spatial and temporal  resolution. We demonstrate how stimulated Raman detection of an X-ray probe   may be used to monitor the phase and dynamics of the nonequilibrium valence   electronic state wavepacket created by e.g. photoexcitation, photoionization   and Auger processes. Conical intersections (CoIn) dominate the pathways and   outcomes of virtually all photophysical and photochemical molecular processes. Short X-ray pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based   on a coherent Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the vibronic coherences (rather than   populations) that are generated as the system passes through the CoIn. X ray   sum frequency generation, and detecting molecular chirality. Coherences at   conical intersections are probed by X-Ray stimulated Raman signals. Contrary   to our common picture of a short femtosecond and precisely timed nonadiabatic   passage, the coherence signature lingers for a much longer time.

Conical intersections (CoIns) are ubiquitous features on molecular potential energy surfaces (PESs) where the   Born-Oppenheimer approximation breaks down. They determine the outcome of  virtually all photochemistry and –physics, by opening non-radiative and ultrafast relaxation channels after optical excitation. Prominent examples   include the primary initiation of vision or the ability of nucleobases in the   genetic code to resist UV radiation. The existence of CoIns as fundamental features   is widely accepted, yet their direct observation has so far eluded   experimental efforts. Strong evidence for CoIns usually is based on the   observation of ultrafast internal conversion rates via electronic state   populations. Stimulated Raman probes of Uracil, with energy bandwidths able   to resolve the potential energy splitting at the CoIn seam, map the   electronic coherence at the CoIn in real time. The chaotic nature of x-ray   free-electron-laser pulses is a bottleneck that has limited the joint temporal   and spectral resolution of spectroscopic measurements. We show how to use the   correlations of the stochastic x-ray field to overcome this difficulty by   correlation signals averaged over independent pulse realizations. We further   demonstrate that core excitations in molecules can be manipulated by placing   them in X ray cavities, to form hybrid light matter excitations known as polaritons.

[1] Visualizing Conical Intersection Passages via Vibronic Coherence Maps Generated by Stimulated X-Ray Raman Signals”,   Daniel Keefer, Thomas Schnappinger, Regina de Vivie-Riedle and Shaul Mukamel. PNAS (2020) http://arxiv.org/abs/2008.06191

[2] “High temporal and spectral resolution of   stimulated x-ray Raman signals with stochastic free-electron-laser pulses”,   Stefano M. Cavaletto, Daniel Keefer, and Shaul Mukamel. (In preparation)

[3] “Manipulating core-excitations in   molecules by X-ray cavities”, Bing Gu, Artur

 


返回原图
/