1. Isotopic Effect in Bond Rearrangement Caused By Sudden Single and Multiple Ionization of Water
Mat Leonard, A. Max Sayler, Kevin D. Carnes, Brett Esry, and Itzik Ben-Itzhak
J.R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506
ACKNOWLEDGMENTS
Thanks to Mark A. Smith, Jiangfan Xia, Jack W. Maseberg, and Dag Hathiramani.
Supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U. S. Department of Energy.

2. Bond rearrangement H H C C H H C C An example: Acetylene Vinylidene
Osipov et al., PRL 90(23), (2003)

3. Our main interest Xq+ + H2O → H2O+ + e- + Xq+ H2+ + O
Ionization & Dissociation of water by fast charged particles (i.e. ionizing radiation) e-, H+, Xq+, (hν) + H2O 
In particular:
H+ + H2O
4 MeV
Xq+ + H2O → H2O+ + e- + Xq+
H2+ + O
Does the H2+ actually come from water?

4. Where does the H2+ come from?
Pressure dependence shows H2+ from H2O+ is the dominant source of H2+ above ~ 1 × 10-6 Torr.

5. Experiment Schematic Target cell containing Fragments accelerated
water vapor
Fragments accelerated
by electric field +
Bunched Beam, F7+ E
Faraday Cup _
Time of flight 
Fragments
The buncher signal starts the clocks.
Detector
The first particle stops the first clock and so on…

6. Typical Data

7. Bond rearrangement in single ionization of water
Note that H2O+ → H2+ + O
is about twice as likely as
D2O+ → D2+ + O, with
HDO+ → HD+ + O in between.
A.M. Sayler et al., AIP 576, 33 (2001)
Electron impact data from:
Straub et al., J. Chem. Phys. 108, 109 (1998)

8. “Slow” Mechanism Slow How would this process change
tcol ~ 1 a.u.
How would this process change
upon isotopic substitution?
As the fragments separate, the
protons share the electron

9. “Fast” Mechanism Sudden How would this process change
tcol ~ 1 a.u.
Sudden
The protons happened
to be at the right separation
How would this process change
upon isotopic substitution?

10. Is bond rearrangement in multiple ionization real?
Momentum conservation!
A.M. Sayler et al., AIP 680, 48 (2003)

11. Bond rearrangement in multiple ionization
19 MeV F7+ + H2O

12. Bond rearrangement in double and triple ionization of H2O
F7+ + H2O at 1 MeV/amu
Results:
H2+ + O+
H2+ + O3+
=  %
= I’ll get around to it
H+ + OH+
H+ + OH+
H2+ + O2+
=  %
H+ + OH+

13. Bond rearrangement in double ionization of D2O
Results:
D2+ + O+
D+ + OD+
= ± %

14. Isotopic effect in double ionization of water
H2+ + O+
= ± %
H+ + OH+
= ± 0.033!
Double Ionization
D2+ + O+
D+ + OD+
= ± %
H2+ + O
= ± %
H2O+
= ± 0.047
Single Ionization
D2+ + O
= ± %
D2O+

15. Sudden ionization – fragmentation
H+ + OH
H+ + OH
≈ 67 %
OH+ + H
Mostly H2O+
Dissociation to OH+ + H
is energetically favored
over H+ + OH
OH+ + H
Pair PECs from:
Chen PhD 1991
Kołos et al., J. Chem. Phys. 84, 3278 (1986)
Werner et al., J. Chem. Phys. 79, 905 (1983)
H-O-H angle at 104.5°

16. The bond rearrangement channel is very small but not significantly slower than other fragmentation processes
O + H2+
H2+ + O
≈ 0.9 %
OH + H+
Dissociation to OH + H+
is energetically favored
over H2+ + O
In addition, the OH + H+
dissociation path is
kinematically favored
O-H bonds held equal

17. Isotopic preference is caused by the increasing
spread of the initial nuclear wave function
O + H2+
O + D2+

18. An interesting observation
H2+ + O2+
Note that
=  ~ 1/3
H2+ + O+
while
Ne3+
=  0.006
Ne2+
Ar3+
=  0.003
Ar2+
CO3+
=  0.02
CO2+
BR seems to be a
constant fraction of H2Oq+
Heber et al. Phys. Rev. A 52, 4578 (1995)
Ben-Itzhak et al. Phys. Rev. A 47, 2827 (1993)

19. Summary
Bond rearrangement – forming H-H+ bond upon dissociation of transient water molecular ion
Bond rearrangement occurs in single and multiple ionization
An isotopic effect has been observed in single and double ionization, bond rearrangement is more probable for less massive isotopes.
The data suggests that bond-rearrangement is approximately a constant fraction of each ionization level
A sudden mechanism is suggested in which the matching of the initial and final states are the key factor
Future work
Theory –time evolution of the nuclear wave functions on the PES of H2Oq+

20. Motivation Fun along the way Isotopic Effect Radiation damage
Ionizing Radiation
Radiation damage
Ionization caused mostly by secondary e-
Ionized and dissociated water damages DNA
Cell e- e- e- H+
OH+ OH OH
Fun along the way
Isotopic Effect