Gas Phase Infrared Spectroscopy of Protonated Species Department of Chemistry University of Georgia Athens Georgia, Allen M. Ricks, Gary E. Douberly, Michael A. Duncan

Protonated Molecular Complexes, Metal Ion Ligand Complexes, and Carbocations H + (CO 2 ) n -Ohio State 2007 H + (C 2 H 2 ) n -Ohio State 2007 M + (H 2 O ) n -M108, M109 Carbocations-RB08, RB09 IR Spectroscopy probes fundamental bonding interactions and structures.  Ligand vibrational shifts  Structures, isomers  Coordination spheres  Solvation  Intracluster reactions Protonated Species: H + (CO) 1,n>3, H + (N 2 ) 1,2, H + (Acetone) 1,2

Previous Work J. R. Roscioli, L. R. McCunn, M. A. Johnson, Science, 2007, 316, 249 G. E. Douberly, A. M. Ricks, B. W. Ticknor, M. A. Duncan, Phys. Chem. Chem. Phys., 2007, 10, 77

Experimental Setup kV discharge through a supersonic expansion gas mixture Mass selection in first flight tube Intersection of ions and photodissociation laser in reflectron Spectra obtained via monitoring photodissociation as a function of laser wavelength Can continuously tune cm -1 ~1 cm -1 linewidth

Obtaining Spectra on a Zero Background hνhν

H + CO Electron donation from metal into anti- bonding orbital leads to red shift of CO stretch Electron withdrawing effects blue shifts CO stretch Free CO stretch is at 2143 cm -1 HCO + stretch is at 2184 cm -1 Ar HCO + at 2134 cm -1 “Theoretical Analysis of Bonding Between CO and Positively Charged Atons” A. Lupinetti, S. Fau, G. Frenking, S. Strauss J. Phys. Chem. A., 1997, 101, 9551

H + (CO) n>2 Proton asymmetrically shared in protonated CO dimer Dimer “core” preserved in larger H + (CO) n clusters 3 8 J. Szymczak, S. Roszak, R. Gora, J. Leszczynski, J. Chem. Phys, 2003, 119, 6560

CCSD(t) cc-pVDZ H + (CO) n 3 8

H+N2H+N2 Previous work by Dopfer et al. 1 Proton causes ~300 cm -1 redshift of N 2 stretch Multiple argon atoms cause further redshift [1] S. Nizkorodov, M. Meuwly, J. P. Maier, O. Dopfer, J. Chem. Phys., 1998, 108, 8964

H + (N 2 ) 2 Proton symmetrically shared In-plane proton motion has massive oscillator strength (~5000 km/mol) Combination bands with proton motion?

Anharmonic Calculations Generate quartic force fields at high levels of ab inito theory Include argon messanger atom in calculation Hopefully obtain combination band and overtone frequencies and intensities New technologies allow broader tuning range Obtain spectra of larger H + (N 2 ) n clusters

Acknowledgements The NSF for funding Assistant Prof. Gary Douberly (Fall ’08) Prof. Mike Duncan The Duncan Lab