JRA3: Cold and Complex (Biomolecular) Targets
Why study interaction of HCI with biomolecular targets?
• Basic physics: large energy transfer in a single collision!
• Applied physics: HCI as secondary products, e.g. in radiation therapy
Why “cold” targets?
• All molecules in one electronic (ground-) state
• Possibility of recoil momentum spectroscopy
Co-ordinators:
Thomas Schlathölter and Reinhard Morgenstern
Tasks and Volunteers
A. Solid biomolecular targets, CEA/Caen (Huber, Lebius)
B. Ionic biomolecular targets NUI/Maynoth (O’Neill, v.d. Burgt) QUB/Belfast
(Greenwood, Williams, McCullough, OUL/London (Mason),
KVI/Groningen (Schlathölter, Morgenstern)
C. Neutral gasphase biomolecular targets CUB/ Bratislava (Matejcik), OUL/London (Mason), UIBK/Innsbruck (Scheier, Märk), LCAR/Toulouse (Moretto
Capelle)
D. Ultracold neutral targets (nanodroplets, MOT’s) UBI/Bielefeld (Stienkemeier, Werner), OUL/London (Mason), KVI/Groningen (Schlathölter, Morgenstern)
E. Datareduction and analysis UBI/Bielefeld (Werner),
A. Solid biomolecular targets
In the case of a nucleic bases, a compressed powder is used as a 'solid' target, which can be bombarded with ions of different charges and energies, and at different incidence angles. Fragmentation spectra are analysed with mass-spectrometric methods.
DeOxyAdenosine
0
1000
2000
3000
0 40 80 120
= 5°
*10
cou
nts
0
100
200
300
0 40 80 120
= 0°
*10
mass/charge (a.u.)
50
100
150
0 40 80 120
= 10°
O2+
(40 keV) + thymidine
inset part magnified by a factor 10
Huber et al, Caen
Dependence of the fragmentation of thymidine on the incidence angle
(m=241)
B. Ionic biomolecular targets
Adaption of MALDI techniques
Desorption laser Desorption of
ions and neutrals
Laser
QUB arrangement to study neutral targets
Pulsed ion beam
the principle to get an ionic target
MALDIsample
(located in a trap endcap)
laser pulse
matrixbio
molecules
3rd or 4th harmonic of our Nd:YAG-laser (355 or 266 nm)
Quantel Brilliant
pulse length: ~5 ns frequency: 50 Hz
fluence: up to 200 mJ/cm2 @ 1064 nm.
MALDI and an electrostatic trap
trapping and cooling of desorbed ions
expandingplume
(neutrals and ions)
trapped ions as target for HCI/fs-laser pulses
ECRISor
fs-laser
YAG laser
trap Einzellens
MALDIsample
reflectron
detector
electrostatic analyzer
ions
TOF analysis by means of a FAST P7888 TDC (1ns resolution, 1ns deadtime, 1 GHz)
Several events per sweep: possibility of coincidence experiments
fields are switched off for MCI bunch passage!
measurement cycle1) laser desorbed ionic biomolecules are introduced from one electrode of the trap
trap/TOF tandem leads to high mass resolution which can be extended to high m/q values allowing for the study of
large biomolecules.
1) reflectron2,3)
3) the trapping potentials are switched of
2) ions are accumulated and cooled
4)
4) a pulse of MCI passes the trapping region through the ring electrode
6) ions pass a reflectron TOF spectrometer
5)
5) a dc pulse applied to the second end cap extracts molecular ions and fragments
C. Neutral gasphase bio-molecular targets
Target production via evaporation possible for DNA or RNA building bloks like thymine or uracil
Problem: Are the molecules in their electronic groundstate?
Approach for a solution: Check via reactions which are sensitive for electronic state
Example: H-loss or fragmentation in low energy attachment reactions
Electron attachment (Scheier, Märk)
Thymine
Uracil
0 1 2 3 40
1
2
3
4
Electron energy (eV)
Cro
ss s
ectio
n (1
0-20 m
2)
(×0.33)
Glycine
M + e‾ → (M-H)‾ + H
P. Scheier, T. Märk
D. Production and manipulation of ultracold targets
• Capture in magneto-optical traps (MOT’s)
• sympathetic cooling of molecules in a MOT
• Capture of biomolecules in He nano droplets
Ultra cold Na target in a Magneto Optical Trap (MOT)
near resonance laser light to trap and cool Na atoms:
•Load from background vapor•106 –107 Sodium atoms•sub mm size cloud•200-300 K (<30 neV!)
laser light + magnetic quadrupole field = MOT
P P-hn
red detuned light
Spontaneous emission
TOF and recoilspectroscopy of O6+ + Na collisions
-12 -10 -8 -6 -4 -2 0 2 40
10
20
30
40
50
60
70
80
90
100
110
tra
nsve
rsal
mo
me
ntu
m
longitudinal momentum-12 -10 -8 -6 -4 -2 0 2 40
10
20
30
40
50
60
70
80
90
100
110
tra
nsve
rsal
mo
me
ntu
m
longitudinal momentum
Na4+
-12 -10 -8 -6 -4 -2 0 2 40
10
20
30
40
50
60
70
80
90
100
110
tra
nsve
rsal
mo
me
ntu
m
longitudinal momentum
Na3+ Na2+
Apparatus for He nanodroplet studiesToennies et al , Physics Today, Feb. 2001, 31-37
Helium droplet beam Helium droplet beam machinemachine
Fakultät für PhysikFakultät für Physik
Formation of large molecular complexes in helium Formation of large molecular complexes in helium dropletsdroplets
0.00.20.40.60.81.0 (PTCDA)
n in helium droplets
Rel
. Fl
uore
scen
ce
0.0
0.2
0.4
0.6
0.8
1.0
Abs
orpt
ion
PTCDA on quartz
17000 19000 21000 23000 250000.0
0.2
0.4
0.6
0.8
1.0 PTCDA monomer spectrum
Rel
. Fl
uore
scen
ce
Wavenumber [cm-1]
Formation of large molecular complexes in helium Formation of large molecular complexes in helium dropletsdroplets
M. Wewer and F. Stienkemeier, Phys. Rev. A 37, 2002
Spectroscopy of excitonic transitions in PTCDA nanostructures at 380 Spectroscopy of excitonic transitions in PTCDA nanostructures at 380 mKmK
Laser induced fluorescence
spectrum of PTCDA
(a) in a nanodroplet (b) in the gasphase
F. Stienkemeier and A.F. VilesovJ. Chem. Phys.115 (2001) 10119
E. Data reduction and analysis
A non-trivial task!
High-dimensional parameter space! (up to 30-40 parameters per collision event)
Pattern recognition
Fitting procedures based on e.g. maximum entropy methods
2000
4000
6000
0 40 80 120
Xe20+ (400 keV)
Aq+
+ thymidine ( = 0°)
0
100
200
300
0 40 80 120
O2+ (40 keV)
mass/charge (a.u.)
cou
nts
Xe20+, 400 keV
O2+, 40 keV
Huber et al, Caen
NIM B 205 (2003) 666–670
Fragmentation of thymidine by ions with high and low
charge
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