Wave packet dynamics in atoms and molecules

1
Wave packet dynamics in atoms and molecules

• Eva Heesel
• Corinne Glendinning
• Helen Fielding
• Department of Chemistry
• University College London
• UCL Progress Report at RAL Attomeeting on
  07.12.2005

2
Interferometer and Ramsey Fringes

• Interferometer
• Stabilisation program completed
• Breadboard under investigation
• Ramsey Fringe Experiment
• Filter for wavelength selection under way
• Need kHz gas jet, TOF chamber, full beam line
• Can generate high-order harmonics from each
  interferometer beam observe fringes (XUV SPIDER
  -Oxford report). Can also characterise bandwidth.

3
Krypton experiment (Corinne)

• Use time-resolved photoelectron spectroscopy to
  look at low n Rydberg states
• Excitation of Kr 4s2 4p5(2P3/2) 6s, 7s and 5d
  Rydberg states from the
• ground state via 5p intermediate
• A VUV pulse will then ionise the Kr core further
  or ionise the Rydberg electron
• Relate different core excitations to core-
  Rydberg electron distances
• Double ionisation of Kr core opportunity to
  study the dynamics of the
• Rydberg electron in the presence of a doubly
  charged core
• If photoelectrons are detected by imaging, the
  l- character of the Rydberg
• states can be reconstructed

4
Kr Energy levels
60
Kr 4s4p5(1P1) LIMIT 55.9499
Kr(4s2 4p3 4 S)4d (5D0,1,2,3,4) LIMITS
55.5247, 55.5277, 55.5289, 55.5303,55.5498
50
Kr 4s4p5(3P2,1,0) LIMITS 52.7330, 53.1607,
53.4289
Kr (1S0) LIMIT 42.4608
40
Kr (1D2) LIMIT 40.1751
Kr (3P2,1,0) LIMITS 38.3595, 38.92338, 39.01817
Energy (eV)
30
VUV
HHG
20
Kr(2P1/2) LIMIT 14.6654
800 nm
Kr(2P3/2) LIMIT 13.9996
10
6 fs
Kr 4s24p5 (2P3/2) 5d 27/2 J3 23/2 J2,1
25/2 J2,3 Kr 4s24p5 (2P1/2) 6s
21/2 J1 Kr 4s24p5 (2P3/2) 7s 23/2 J2,1
(range 13.00- 13.11 eV)
214 nm
OPA
0
1S0
Kr 4s24p5 (2P3/2) 5p 23/2 J2 11.5458
5
Two-stage plan for Kr experiment

• At UCL Measure frequency-resolved spectrum
• Narrowband Use ns beams 214 nm and 800 nm
• Can do experiment both field-free and with static
  field (Stark splitting)
• Photoionise Rydberg states with 400/800 nm photon
• Field-free apply field with 20 ns rise time to
  extract ions
• With static field investigate Stark shifts (good
  test for imaging) (detect electrons)
• At IC Measure electron dynamics image
  photoelectrons
• Use 214 nm ns beam (OPO) and 200 nm fs beam (FHG
  from few-cycle pulse)
• Need static field for imaging.

6
Benzene experiment (Eva)

• Monitor ultrafast dynamics of benzene molecule
  using time- resolved photo- electron spectroscopy
• Excitation of benzene molecules from the ground
  state S0 to the S2 state with
• 200 nm photons (pulse duration as short as
  possible)
• The S2state decays very fast (lt 50 fs) by
  internal conversion to high
• vibrational levels of the S1 and S0 states.
• Time-delayed probe photon ( 50-100 eV) can
  ionise populations from all
• electronic states Detect photoelectrons with
  different kinetic energy
• Energy resolution given by
• a) pulse duration (bandwidth) - 0.35 eV for 5
  fs pulse
• b) resolution of photoelectron spectrometer
  (1)

7
Benzene Energy levels
Energy (eV)
VUV probe has the advantage of being able to
ionise all intermediates and products
I.P.
9.24
S2
6.02
S1
4.75
VUV (e.g. 50-100 eV)
200 nm (6.2 eV)
S0
8
Plans/work in progress

• Generation/Characterisation of 200 nm
• Generation Fourth-harmonic of 800 nm
• Characterisation cross-correlation, two-photon
  ionisation,.
• Calculations
• Mikes Robb group (IC chemistry)
• Wave packet moves through
• conical intersection