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

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

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

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

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

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

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

3500 3600 3700 3800 Photon Energy, cm-1

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

(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

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

(H2O)7¯ · Arn II I I' Electron Binding Energy (eV) Isomer I n = 8 10 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)

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

(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)

(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

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

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

(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

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¯

Acknowledgments