1. T. L. Guasco, B. M. Elliott, M. Z. Kamrath and M. A. Johnson
Isotopomer selective infrared predissociation spectroscopy of charged water clusters
T. L. Guasco, B. M. Elliott, M. Z. Kamrath
and M. A. Johnson

2. Predissociation Dip Spectroscopy
Coaxial TOF
Reflectron
Detector
±1.5 keV
hnpump
(scanned)
hnprobe
(fixed)
A schematic of the double resonance, IR2DR, method. The integration of the coaxial TOF enables the triple focusing necessary for the pump/probe methodology.The black inset trace shows the typical mass spectrum of NO2‾ · H2O resulting when both lasers are tuned to vibrational resonances. The blue and red inset traces are the prdissociation spectra obtained by monitoring the arrival of the fragments resulting from the ion packet interacting with the pump and probe lasers, respectively, as the pump laser frequency is scanned through the infrared.
pump fragment
Signal
probe fragment
Time of Flight, ms

3. H2DO+ · Ar Predissociation Yield Photon Energy, cm-1 2200 2400 2600
2800
3000
3200
3400
3600
3800
Photon Energy, cm-1

4. Isomers of H2DO+ · Ar
2400
2600
2800
3000
3200
3400
3600
3800

5. H5O2+ · RG nsp na B) H5O2+ · Ne ns Predissociation Yield A) H5O2+ · Ar
1000
1500
2000
2500
3000
3500
Photon Energy, cm-1

6. H4DO2+ · Ar
3400
3500
3600
3700
3800
2400
2500
2600
2700
2800
Ar end
Ar-bound
Free end
experimental
shared D

7. H4DO2+ · Ar Predissociation Yield Photon Energy, cm-1 800 2400 2800
1200
1600
2400
2800
3200
3600
Photon Energy, cm-1

8. 3500
3600
3700
3800
Photon Energy, cm-1

9. Predissociation Yield
800
1200
1600
2400
2800
3200
3600
Photon Energy, cm - 1

10. (H2O)n¯ HOH bending region (H2O)4 ¯· Ar6 Bare water Sharp feature
Photon Energy, cm-1
1400
1500
1600
1700
1800
HOH bending region
(H2O)4 ¯· Ar6
Bare water
Sharp feature
red-shifted
relative to bare
water molecule

11. Double acceptor or “AA” water molecule contacts electron cloud
H2O bend
OD stretch
(H2O)4–·Ar6 //
(D2O)4–·Ar6 C D AA
Calculated Intensity // A B
Predissociation Yield
Double acceptor or “AA” water molecule contacts electron cloud //
1400
1500
1600
1700
1800
2400
2500
2600
2700
2800
Photon Energy, cm-1 11

12. (H2O)7¯ · Arn II I I' Electron Binding Energy (eV) Isomer I n = 810 8
Isomer I' 6 5
Isomer II 4 2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Electron Binding Energy (eV)

13. (H2O)7¯ · Arn * Photon Energy, cm-1 Isomer I AA AA Isomer I' Isomer II
1600
3200
3400
Photon Energy, cm-1

14. (H2O)6¯ · D2O · Arn A) B) * * * Relative Ion Intensity TOF (msec) 50
(H2O)6-·Ar
(H2O)6-
(H2O)7-·Ar
(H2O)3-·Ar
Relative Ion Intensity B)
D2O·(H2O)6- * * * 50 55 60 65 70
TOF (msec)

15. (H2O)6¯ · D2O · Arn * Photon Energy, cm-1 AA HOD AA 2400 2600 2800
1000
1200
1400
1600
2400
2600
2800
3000
3200
3400
3600
3800
Photon Energy, cm-1

16. Isomer Selective Spectroscopy of OD stretches Associated with AA water (H2O)6¯ · D2O · Arn
By probing OD bands we are able to definitively isolate the contributions from a single water molecule
2400
2500
2600
2700
2800
Photon Energy, cm-1

17. Isomer Selective Spectroscopy of OD Stretches Associated with Scaffold Water Molecules of (H2O)6¯ · D2O · Arn
By probing OD bands we are able to definitively isolate the contributions from a single water molecule
2400
2500
2600
2700
2800
Photon Energy, cm-1

18. (H2O)6¯ · D2O · Ar5 Double Resonance Results
Pump: 2400 – 2800 cm-1
Probe: 1138 cm-1 (AA DOD Bend)
1000
1200
1400
1600
1800
2400
2600
2800
Photon Energy, cm-1

19. Conclusions
Successful extension of isomer selective infrared predissociation technique to isotopomers
Isolation of isomers with significant spectral overlap in H4DO2+· Ar
Verification of bands associated with “AA” water in (H2O)n¯

20. Acknowledgments