Photoabsorption and photoionization

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VUV Photochemistry with Synchrotron Radiation,
Daresbury, 11th September, 2003
Photoabsorption and photoionization of reactive
species
Stefano Stranges Department of
Chemistry University of Rome La Sapienza
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Overview

• introduction (SR features ..)

• Photoabsorption and Photoionization of free
  radical
• and transient molecules (LPL - _at_ GAS PHASE,
  POLAR)

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ELETTRA Synchrotron Laboratory (Trieste, Italy)
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3rd generation synchrotron radiation features

• ? tunable source over a wide energy range

? high photon flux and resolution used
simultaneously

• high degree of polarization,
• CPL (POLAR) and LPL (GAS PHASE beamline)

? time structure time resolved experiments
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radical and transient free molecules
high photon energy resolution AND flux photon
band pass lt intrinsic broadening
(core-hole lifetime) high
photon flux --gt heavily diluted samples
(highly reactive gas
phase species)
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detailed spectroscopic studies of core and
inner-shell processes in radical and transient
species CS (S2p) O3 (O1s)
OH (O1s) CH3 (C1s)
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CS (X 1S) ground state electronic
structure (1s)2 (2s)2 (3s)2 (4s)2
(1p)4 (5s)2 (6s)2 (2p)4 (7s)2
(3p)0(8s)0 Ryd S 1s C 1s S 2s S
2ps S 2pp
S (2p) inner-shell excited states S 2ps
-gt3p 1P?, 3P S 2pp -gt3p 1S?, 3S, 1S-, 3S-,
1D, 3D??????????? (8 electronic Terms)
Selection rules in LS coupling DS0
????????DL???0, ?1 S?????S ?????????DL??0 (q0
?) ?parallel transitions (DMj 0) S ? P
????????DL? 1 (q90?) perpendicular
transitions (DMj 1)
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CS sulphur L-edge absorption
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FC analysis adopting the PCI line shape by van
der Straten (Z.. Phys. D8 (1988) 35)
MF splitting 50 meV SO splitting 1.18 eV
adiabatic IE values for the S(2p-1) states
2S 171.38 eV (v 0)
2P3/2 171.43 eV (v 0)
2P1/2 172.58 eV (v 0)
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OH in situ generation
H NO2 --gt OH NO (rate constant 69.3 x
1012 cm3 mol-1 s-1)
OH OH --gt H2O O ( 1.14 x 1012 cm3 mol-1
s-1) O OH --gt O2 H ( 20 x 1012 cm3
mol-1 s-1)
studies OH ( XPS, XAS ) 1s2 2s2 3s2 1?3
OH (X 2P) OH (O1s-1 3,1P )
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? XPS O1s-1 OH ( 1,3 P?)
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? XAS O1s-1 OH ( 2???)
S. Stranges et al., JCP, 116 (2002) 3676
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Direct observation of intermediate species (OH,
2S) formed in femtosecond dissociation processes.
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flash pyrolitic source
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CH3 C K-edge absorption
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(A1, A1, E, E) , ?sym strech, ?sym BOPL
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i) O 2p--gtns, 2p--gtnd (3D, 3P, 3S) Rydberg
states converging to the second ionic state
O(2D).
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Possible perspectives

• SELECTIVITY
• 3D-Electron-Ion Momentum Coincidence
  Spectroscopy

• High Resolution TPE-PICO

• HR PES ( ion coincidence detection)

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• Photoabsorption and ionization of free radical
  and transient molecules
• (LPL - _at_ GAS PHASE, POLAR)
• - GAS PHASE RT M. Alagia, R. Richter ...
• - Dr. M. Lavollee (CNRS, LURE, Orsay, FR)
• - Prof. N. Kosugi, UVSOR, IMS Okazaki, Japan
  (CS)
• - Prof. P. Decleva, G. Fronzoni (OH), Univ. of
  Trieste (Theory)
• - Prof. J.M. Dyke, Prof. J.B. West (ARPES, CIS)

• Financial support
• - University of Rome,Dip. of Chemistry (MIUR
  grants)
• - INFM (National Institute for Physics of Matter)
• - CNR (Italian National Research Council)
• - Sincrotrone Trieste (ELETTRA Synchrotron
  Laboratory)