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Projects
Polarized X-Ray-Emission
Spectroscopy (Photon in – photon out spectroscopy)
X-ray
scattering / emission: Basic Processes
Core
excitation of the target molecule, followed by relaxation of the molecule
through photo-emission. We define
K-beta emission as photons emitted from electrons which are dropping from the
valence shells to the empty core hole (this case 1s). K-alpha emission occurs when the electrons in an upper core
hole (this case 2p) fills the empty
core hole (this case 1s).
Current
experiments in polarized x-ray-emission spectroscopy take place at the ALS’s
beamline 9.3.1 using our new x-ray emission endstation.  
Our
initial experiments have taken advantage of the atomic-site selectivity
inherent to core-level spectroscopy (i.e., core levels for different atoms
are well separated in energy), to study particular atomic sites in molecules.
Over the last few years we have investigated molecular systems such as
Cl-containing methane-derivatives (CF3Cl, CF2Cl2,
etc.), HCl and Cl2. We are
now moving on to other materials such as CdTe and CdO used in solar cell
research.
Resonant
Inelastic X-ray Scattering (RIXS): The
incident x-ray is sufficient to resonantly remove a core-level electron to a
higher unoccupied excited state.
Relaxation of this core-hole state is a two step process, an inner
shell electron filling the hole while simultaneously an x-ray photon is
emitted.
Non-Dipole: The dipole approximation refers to the
assumption that the expansion of exp(ik·r) for the interaction with
the radiation field can be set equal to unity if k·r is small. Previous non-dipole measurements at the
ALS using electron time-of-flight techniques indicate that the extent and
significance of these effects is larger than might be expected. For these
experiments we must carefully study how the x-ray emission spectra change
depending upon the emission polarization angle relative to the incoming
photon beam axis.
Molecular Photoionization and
Photofragmentation Dynamics
Anion/Cation Spectroscopy:
Molecular Photofragmentation:
Atomic Photoionization:
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