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SUMMARY:Probing Ultrafast Electron Motion with Attosecond X-ray Free Elect
 ron Lasers
DTSTART:20260423T171500
DTEND:20260423T183000
DTSTAMP:20260403T235712Z
UID:da04115da59c7fe71af744383cabae0b68d1ab6f716bf6a7a0a778fb
CATEGORIES:Conferences - Seminars
DESCRIPTION:James Cryan\, Stanford Univ. / SLAC\nThe ultrafast motion of e
 lectrons is a frontier problem for photochemical processes\, as electron m
 otion is a key ingredient of all chemical reactions. Electronic rearrangem
 ent is also the means by which light energy is harnessed in photochemistry
 . The timescale for coherent electron dynamics is set by the energetic spl
 itting of the electronic states\, which in small molecular systems\, is on
  the scale of an electron volt (eV). This sets the natural timescale for e
 lectronic motion to be few-to-sub femtosecond (fs).\n\nTo approach these e
 xtreme timescales\, we can use short pulses of light to excite small quant
 um systems. For instance\, the impulsive interactions between a light fiel
 d and a quantum system can induce time-dependent oscillations in the charg
 e density. Such electronic wavepacket motion (in the absence of nuclear mo
 tion) has come to be referred to as charge migration [1]. While the initia
 l charge dynamics following impulsive excitation (or ionization) begins as
  purely electronic motion\, this wavepacket will couple to other degrees o
 f freedom in the system (i.e. nuclear motion or chemical dynamics) and lea
 d to localization of the charge.  The transfer of electronic charge acros
 s molecular bonds is fundamental to an understanding of charge transfer ph
 enomena.\n\nThe study of these fundamental phenomena requires state-of-the
 -art light sources\, such as the Linac Coherent Light Source (LCLS)\, an X
 -ray free electron laser (XFEL) facility which produces high-brightness\, 
 ultrashort pulses\, with wavelength continuously tunable across the x-ray 
 regime. Schemes to provide isolated\, sub-femtosecond pulses from an FEL a
 re being explored at facilities world-wide\, and recently we have demonstr
 ated such pulses at the LCLS [2]\; opening the door for time-resolved meas
 urements of ultrafast electron dynamics on their natural timescale. In my 
 talk\, I will highlight our recent developments in probing electronic moti
 on in small molecular systems. We have employed sub-femtosecond pulses fro
 m the XFEL to study ultrafast charge dynamics in both core-excited [3\,4\,
 5] and low-lying cationic systems [6]. We are also developing nonlinear x
 -ray spectroscopies [7\,8] to initiate and control electron dynamics. The 
 control of coherent electron motion represents a significant step towards 
 achieving charge-directed reactivity [9]\, a grand challenge for the field
  of attosecond science.\n\n[1] Cederbaum and Zobeley 1999 Chemical Physics
  Letters 307 205–210\n[2] Duris and Li et al. 2020 Nature Photonics 14 3
 0-36\n[3] Li and Driver et al. 2022 Science 375 285-290\n[4] Driver et al.
  2024 Nature 632 762-767 (2024)\n[5] Wang and Driver et al. Phys. Rev. X 1
 5 011008 (2005)\n[6] Driver et al. ArXiv:2411.01700\n[7] O’Neal et al. 2
 020 Phys. Rev. Lett. 125 073203\n[8] Biggs et al. 2023 Proc. Nat. Acad. Sc
 i. 110 15597-15601\n[9] F. Remacle\, R. D. Levine\, and M. A. Ratner 1998 
 Chem. Phys. Lett. 285\, 25\n 
LOCATION:CH G1 495 https://plan.epfl.ch/?room==CH%20G1%20495 https://epfl.
 zoom.us/j/67570484652?pwd=UpB6UFTCS3n1QpxlIaYM2UvuMD3tkr.1
STATUS:CONFIRMED
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