Temperature Dependence of Rb + (H 2 O) n and Rb + (H 2 O) n Ar (n=3-5) Cluster Ions Amy L. Nicely OSU International Symposium on Molecular Spectroscopy June 19, 2007

2 Outline Apparatus and formation of cluster ions Supporting calculations Rb + (H 2 O) n vs Rb + (H 2 O) n Ar experimental and calculated IR spectra

3 Triple quadrupole mass spectrometer ● Neutral clusters are formed via a supersonic expansion ● Fully expanded neutral clusters collide with alkali cations produced via thermionic emission ● MS-MS method: select parent ion cluster, dissociate with IR laser, detect fragment ion Source lenses Detector lenses Cross beam ion gun Ion selecting quadrupole Ion analyzing quadrupole Ion guiding quadrupole CD/CEM Nozzle Nd 3+ :YAG Laser (1064 nm) 10 ns pulse 10 Hz Tunable OPO/ OPA

4 Evaporative Cooling ● Cooling efficiency determined by the evaporating ligands’ binding energy ● Most weakly bound ligand evaporates to cool cluster, removes both mass and energy E final [Rb + (H 2 O) 2 ] Energy Δ E ≈ BE H2O E n [Rb + (H 2 O) n ] 0- Δ E ≈ BE Ar E final [Rb + (H 2 O) 2 Ar] E n [Rb + (H 2 O) 2 Ar n ] 0- Energy Terminal temperature ~40 K H 2 O evap. = larger energy loss Terminal temperature ~350 K Ar evap. = smaller energy loss

5 Calculation details Geometries optimized, frequencies and energies calculated at MP2 level with Gaussian aug-cc-pvdz for Ar, H 2 O lanl2DZ for Rb + Gaussian lineshape with 15 cm -1 peak width to calculated frequencies using Swizard Thermodynamics data obtained using thermo.pl perl script Average cluster temperature calculated using RRKM-EE theory

6 Vibrational Predissociation of Rb + (H 2 O) 3 and Rb + (H 2 O) 3 Ar

7 (2+1) linear 7.04 kJ/mol (3+0) cyclic 1.99 kJ/mol (2+1) bent 0 kJ/mol Rb + (H 2 O) 3 Ar Isomers (3+0) 4.44 kJ/mol 4 calculated isomers with relative D o values Energy order independent of Ar

8 Rb + (H 2 O) 3 spectra

9 Rb + (H 2 O) 3 thermodynamics

10 Rb + (H 2 O) 3 Ar thermodynamics

11 Vibrational Predissociation of Rb + (H 2 O) 4 and Rb + (H 2 O) 4 Ar

12 Rb + (H 2 O) 4 spectra

13 Rb + (H 2 O) 4 thermodynamics

14 Rb + (H 2 O) 4 Ar thermodynamics

15 Rb + (H 2 O) 5 spectra

16 Spectral summary

17 Conclusions Temperature plays a significant role in the formation of different isomers Low temperatures  more hydrogen bonds High temperatures  fewer hydrogen bonds Rubidium is unique in our alkali metal ion study because multiple isomers exist at low temperatures

18 Acknowledgements Dr. James Lisy Ms. Dotti Miller Lisy Group members Mr. Jason Rodriguez Mr. Jordan Beck Mr. Oscar Rodriguez Jr. Mr. Brian E. Nicely Funding NSF UIUC Department of Chemistry

19 Vibrational Predissociation of M + (H 2 O) 3 Ar

20 Vibrational Predissociation of M + (H 2 O) 4 Ar