Transcript Bromine Molecular Interferometer

Iodine Molecular
Interferometer and Inversion
Symmetry
Mat Leonard
Molecular Structure
o Properties of electronic wave functions describe molecular structure
o symmetry
o spatial extent
o localization
o energy eigenvalues
o Traditional photoelectron spectroscopy focused on energy levels
o Time-resolved photoelectron imaging allows insight into other
properties of electron wave functions
Davis I2- Experiment
o Time-resolved photoelectron spectrum
of I2- experiment (Davis, et al J. Chem.
Phys. 118, 999 (2003))
o Ti:Sapphire laser, 90 fs pulses
o Pump with IR, probe with 3hν
o Velocity Map Imaging
Photoelectron Energy
Spectrum Probe only
o From energy conservation, photoelectron
energy spectrum reveals information
about molecular states
Time-Resolved Photoelectron
Energy Spectrum
Probe only
Pump + Probe
Photoelectron Angular
Distribution
Interesting information lies in the
photoelectron angular distribution (PAD)
The PAD can be represented by:
where, θ is the angle between the electron
velocity and laser polarization vectors, β2n
is the anisotropy parameter associated
with P2n, the nth Legendre polynomial
PAD Anisotropy
o β2 varies in time, even after
dissociation is complete (~300 fs)
o Increase in β2 after 350 fs is
attributed to a shallow well in the
long range potential
o Decrease suggested to be related to
localization of electron
o |β4|<0.1, negligibly small and no
time dependence is observed
Electron Localization
o Localization occurs due to mixing of g and
u states (gerade and ungerade refer to
states being even or odd under inversion,
respectively)
o In the absence of an external field, the
overall electron wave function is of the
the form (IA-IB + IAIB-)
o The wave functions for localization on
a particular I atom, i.e. IA-IB or IAIB-,
are obtained from linear combinations
of g ± u states
o External extraction field of 500 V/cm
can induce the g/u mixing
Sanov I2- Experiment
o Time-resolved photoelectron spectrum
of I2- experiment (Sanov, et al J. Chem.
Phys. 123, 054329 (2005))
o Ti:Sapphire laser, 100 fs pulses
o Pump with IR, probe with 2hν
o Extraction field ~40-80 V/cm
PAD Anisotropy
Again, fitting the measured PADs to
we see β2 change long after the
dissociation is complete (~500 fs)
Complete oscillation of the anisotropy
parameter in ~2.5 ps, R≈35 Å
I2- Molecular Interferometer
o Photoelectron with KE=0.12 eV has de Broglie
wavelength λ=35.4 Å
o Effective state mixing occurs when the field
induced perturbation H´=eER is comparable to
the energy separation of the two unperturbed
potential-energy curves
o Electron localization estimated at R≈35.6 Å,
corresponding to ~2.5 ps delay
o β2 varies as R(t)/λ, as expected for double
source interference