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@PHDTHESIS{Xian:308378,
      author       = {Xian, Rui},
      othercontributors = {Miller, Dwayne and Huse, Nils},
      title        = {{A}n atomic perspective of the photodissociation and
                      geminate recombination of triiodide in condensed phases},
      school       = {Universität Hamburg},
      type         = {Dissertation},
      address      = {Hamburg},
      publisher    = {Verlag Deutsches Elektronen-Synchrotron},
      reportid     = {PUBDB-2016-03652, DESY-THESIS-2016-028},
      series       = {DESY-THESIS},
      pages        = {162},
      year         = {2016},
      note         = {Dissertation, Universität Hamburg, 2016},
      abstract     = {The thesis presents progress made towards a thorough
                      understanding of the photodissociation and geminate
                      recombination of triiodide anion (I$_3^-$) in solution and
                      solid state using novel time-resolved spectroscopic and
                      structural methods that have matured in the past decade. An
                      isolated I$_3^-$ has only three degrees of freedom, but in
                      the condensed phase, the case of an open quantum system, its
                      chemistry is transformed because other degrees of freedom
                      from the surroundings (the bath) need to be fully taken into
                      account. This system is a textbook example for understanding
                      dissociation and recombination processes in condensed
                      phases, but unresolved issues about the reaction pathways
                      remain. To probe the issues, firstly, mid-UV pulse
                      shaper-based closed-loop adaptive control as well as
                      open-loop power and chirp control schemes were used in
                      conjunction with single-color pump-probe detection of the
                      yield of the photoproduct diiodide (I$_2^{-\cdot}$) to study
                      the above reaction in ethanol solution. The experiments
                      revealed a strong pump-chirp dependence of the
                      I$_2^{-\cdot}$-yield (as much as 40\% change). Subsequently,
                      two possible mechanisms involving additional reaction
                      channels were postulated in order to explain such effect.
                      Secondly, pump-supercontinuum-probe spectroscopy and
                      ultrafast electron diffraction were performed separately on
                      solid state triiodide compound $n$-(C$_4$H$_9$)$_4$NI$_3$
                      (TBAT). This system was chosen to provide a well-defined
                      lattice for the bath and to avail atomic resolution of the
                      condensed phase reaction dynamics. In the optical
                      experiment, coherent oscillations were observed within a
                      probe delay of 1 ps that bear strong resemblance to the
                      stretching modes of ground-state I$_3^-$ and I$_2^{-\cdot}$
                      fragment, which makes it the first to reliably distinguish
                      the two species in a single measurement. In addition, the
                      spectroscopic signature of a novel intermediate, the
                      tetraiodide anion (I$_4^{-\cdot}$), was identified and its
                      origin is attributed to intermolecular interaction of the
                      iodine radical (I$^{\cdot}$) fragment and a neighboring
                      I$_3^-$ chain. Moreover, a number of phonon modes of as low
                      as $\sim$ 10 cm$^{-1}$ were extracted from the time series
                      data of both optical and electron diffraction experiments
                      using advanced frequency analysis (short-time Fourier
                      transform and continuous wavelet transform) and
                      deconvolution schemes, some with good agreement in
                      frequency, which helped pin down the reaction-coupled modes.
                      In the optical experiment, it was found that the libration
                      modes exhibit a delayed appearance in comparison to the
                      stretching modes, and their frequencies show measureable
                      temperature dependence. These findings reveal the molecular
                      details of the sizeable impact of the photo-induced reaction
                      on the crystal lattice and bring insights to dissociative
                      reactions in organic molecular solids, which have rarely
                      been studied due mainly to their incomplete reversibility.
                      The results can, therefore, serve as the experimental basis
                      for further theoretical developments in the lattice effects
                      on a chemical reaction (promotion, quenching and
                      alteration). Together, these two case studies demonstrate
                      the potential of a comparative and multimodal approach to
                      exploring the broad parameter space (chirp, fluence,
                      polarization, temperature, physical state, etc.) that
                      affects the course of a reaction. Future studies are
                      conceived to examine the dynamical details using shorter
                      optical pulses in targeted spectral regions derived from
                      present experiments, as well as to better resolve the fast
                      molecular modes and confirm the time delay between internal
                      and external modes using shorter and brighter electron
                      bunches.},
      cin          = {CFEL-ARD},
      cid          = {I:(DE-H253)CFEL-ARD-20160914},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      experiment   = {EXP:(DE-H253)REGAE-20150101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)29 / PUB:(DE-HGF)11},
      doi          = {10.3204/PUBDB-2016-03652},
      url          = {https://bib-pubdb1.desy.de/record/308378},
}