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  English.dicp.cas.cn    Posted:2019-03-22
Lecture: Unimolecular Reaction Dynamics Studied by Negative Ion Photodetachment and Attosecond Transient Absorption

Time: March 22th, 2019, 10:00am - 12:00pm
Venue: Conference Room on the First Floor, Energy Fundamentals Building
Lecturer: Daniel M. Neumark, University of California, Berkeley

Abstract:

The unimolecular isomerization of vinylidene (H2CC) to acetylene and the photodissociation dynamics of IBr are investigated using two complementary techniques: high resolution photoelectron spectroscopy of cryogenically-cooled anions and attosecond transient absorption. In the anion experiments, H2CCˉ anions are photodetached to access various vibrational levels of weakly bound H2CC; variations in the peak widths and underlying structure point to highly state-specific isomerization dynamics, thus resolving a long-standing controversy into the isomerization “lifetime” of vinylidene. In the attosecond experiments, IBr is photodissociated with one or two visible photons. The dissociation dynamics are monitored using an attosecond XUV pulse with sufficient bandwidth to probe core-to-valence transitions in both the I and Br atoms. The resulting transient absorption spectra map out the adiabatic and non-adiabatic pathways associated with curve-crossings en route to dissociation.

Introduction:

Prof. Daniel M. Neumark is an internationally recognized scientist in physical chemistry. He is the member of the American National Academy of Sciences, fellow of the American Academy of Arts and Sciences, the American Association for the Advancement of Science, the American Physical Society (APS), the American Chemical Society (ACS), and the Royal Society of Chemistry (RSC). He has received the Irving Langmuir Award from the ACS, the Herbert P. Broida Prize from the APS, and the Chemical Dynamics Award from the RSC. Now he is the member of the board of reviewing editors for Science Magazine, and the panel member of the European research Council.

Prof. Neumark and his research group carry out state-of-the-art experiments to probe fundamental problems in chemical physics. The projects in his laboratories encompass (i) reaction dynamics of bimolecular and unimolecular reactions, in which one maps out in detail the potential energy surfaces on which chemistry occurs, (ii) cluster spectroscopy and dynamics, which explore how the properties of matter evolve with size, and (iii) ultrafast x-ray science, where novel femtosecond and attosecond light source initiate and/or probe dynamics in the soft x-ray regime. Much of his work uses photoelectron spectroscopy of negative ions in either the frequency and time-domain to probe the spectroscopy and dynamics of transient and reactive species. His research has yielded new insights into transition state spectroscopy, the electronic and vibrational spectroscopy of clusters, the photodissociation of reactive free radicals, hydrated electron dynamics in clusters and liquid jets, and the ultrafast dynamics of helium nanodroplets excited by femtosecond soft x-ray pulses.

Contact: CHENG Lina
Phone: 84379702

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