Wave packet dynamics in atoms and molecules

Eva HeeselCorinne Glendinning

Helen Fielding

Department of ChemistryUniversity College London

UCL Progress Report at RAL Attomeeting on 07.12.2005

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.

Interferometer and Ramsey Fringes

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

0

10

20

30

40

50

60

0

10

20

30

40

50

60

Energy(eV)

Kr+ 4s24p5 (2P3/2) 5p 2[3/2] J=2 11.5458

Kr+(2P3/2) LIMIT 13.9996

Kr+ 4s24p5 (2P3/2) 5d 2[7/2] J=3 ; 2[3/2] J=2,1 ; 2[5/2] J=2,3 Kr+ 4s24p5 (2P1/2) 6s 2[1/2] J=1 ; Kr+ 4s24p5 (2P3/2) 7s 2[3/2] J=2,1 (range 13.00- 13.11 eV)

Kr+(2P1/2) LIMIT 14.6654

Kr++ (3P2,1,0) LIMITS 38.3595, 38.92338, 39.01817

Kr++ (1D2) LIMIT 40.1751

Kr++ (1S0) LIMIT 42.4608

1S0

Kr++ 4s4p5(3P2,1,0) LIMITS 52.7330, 53.1607, 53.4289

Kr++(4s2 4p3 4 S)4d (5D0,1,2,3,4) LIMITS 55.5247, 55.5277, 55.5289, 55.5303,55.5498

Kr++ 4s4p5(1P1) LIMIT 55.9499

214 nm

800 nm

VUV

~6 fs

OPA

HHG

Kr Energy levels

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.

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 (< 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%)

Benzene Energy levels

S0

S1

S2

I.P.

Energy (eV)

200 nm (6.2 eV)

VUV (e.g. 50-100 eV)4.75

6.02

9.24

VUV probe has the advantage of being able to ionise all intermediates and products

Plans/work in progress

• Generation/Characterisation of 200 nm – Generation: Fourth-harmonic of 800 nm

– Characterisation: cross-correlation, two-photon ionisation,….

• Calculations– Mike’s Robb group (IC chemistry)

– Wave packet moves through

conical intersection

S 1/S 0

seam

(28D sp

ace)

S0

S0

S1

S2

S1

S0

S0

Dewarbenzene

S0

S1

S0: X 1A1g

S1: A 1B2u

benzvalene

S2: B 1B1u

S4: D 1E2g

ionic covalent

S 1/S 0

seam

(28D sp

ace)

S 1/S 0

seam

(28D sp

ace)

S0

S0

S1

S0

S0

S1

S2

S1

S2

S1

S0

S0

Dewarbenzene

S0

S0

DewarbenzeneS0

Dewarbenzene

S0

S1

S0: X 1A1g

S1: A 1B2u

benzvalene

S0

S1

S0: X 1A1g

S1: A 1B2u

benzvalene

S2: B 1B1u

S4: D 1E2g

ionic covalent

S2: B 1B1u

S4: D 1E2g

ionic covalent

S2: B 1B1u

S4: D 1E2g

ionic covalent