Probing Solvation Effects in IBr - (CO 2 ) n by Photoelectron Spectroscopy Elisa Miller Leonid Sheps, Ryan Calvi, and W.Carl Lineberger JILA, Department of Chemistry University of Colorado 62 nd OSU Spectroscopy Symposium June 18, 2007 AFOSR NSF

Introduction  Equilibrium structure State energies and geometry  IBr -  IBr - (CO 2 )  IBr - (CO 2 ) n, n >1  Dynamics Photodissociation and recombination  IBr - (investigated by A. Sanov and T. Sanford)  IBr - (CO 2 ) n, n >1 (investigated by V. Dribinski and T. Sanford) n = 12n = 8

Photoelectron Spectroscopy X AB - ~ A AB ~ X AB ~ h AB - + h → AB + e - (eKE) Bond length, R Electron binding energy (eBE) Electron kinetic energy (eKE) eBE = h – eKE Results  Change in equilibrium bond length,  R e  Electron affinity (EA)  Vibrational frequency, ω e  Term Energy, T o ωeωe

Experiment Nd:YAG/ OPO/ doubler Acceleration Stack Pulsed Valve Ion Optics  E/E  Electron Gun CCD camera Electron Imaging Velocity Map Imaging Time of Flight Mass Gate e-e- IBr in CO 2 Source Chamber

Velocity Map Imaging (VMI) 2-D raw image 2-D slice through reconstructed 3-D image Photoelectron spectrum v1v1 v2v2 IBr - (300nm) photodetatchment

Velocity Map Imaging (VMI) Bond Distance Energy Photoelectron spectrum X 1  + ground state X1+X1+ X 2  + 1/2 I-Br Bond Length v1v1 v2v2 2-D raw image 2-D slice through reconstructed 3-D image

Photoelectron spectrum Velocity Map Imaging (VMI) X 1  + ground state 3  2 excited state Bond Distance Energy 3232 X 2  + 1/2 I-Br Bond Length v1v1 v2v2 2-D raw image 2-D slice through reconstructed 3-D image

Photoelectron spectrum Velocity Map Imaging (VMI) X 1  + ground state 3  1 excited state 3  2 excited state Energy 33 X 2  + 1/2 I-Br Bond Length v1v1 v2v2 2-D raw image 2-D slice through reconstructed 3-D image

IBr - (300 nm) Photoelectron Spectrum 3  1 ~4.07 eV 3  2 ~3.96 eV X 1  + ~3.3 eV Photoelectron Counts Electron Binding Energy (eV) Photoelectron Counts  R e = Ǻ  R e = Ǻ 3  2 v = 0 3  1 v = 0 Electron Binding Energy (eV)

IBr - Bond Length I-Br Bond Length Energy IBr - ( 2  + 1/2 ) IBr ( 1  + ) IBr ( 3  2 ) IBr ( 3  1 )     R e = (.01) Å R e = Å R e = Å R e = Å

IBr Electron Affinity I-Br Bond Length Energy IBr - ( 2  + 1/2 ) IBr ( 1  + ) IBr ( 3  2 ) IBr ( 3  1 ) T o 1.41 eV T o eV Electron Affinity (EA) 2.51 (.01) eV h eKE EA (IBr) = h - T o - eKE (v ’ = 0)

I-Br bond length Energy I + Br I + Br - D o (IBr) 1.82 eV EA(Br) 3.36 eV D o (IBr - ) = EA(IBr) + D o (IBr) - EA(Br) IBr - Dissociation Energy IBr - ( 2  + 1/2 ) IBr ( 1  + ) EA(IBr) 2.51(.01) eV D o (IBr - ) 0.97 (.01) eV

IBr - (CO 2 ) Photoelectron Spectrum IBr - IBr - (CO 2 ) EA (IBr) 3  2  eBE = 0.15 eV 3  1  eBE = 0.16 eV 1  +  eBE = 0.16 eV IBr - Summary Results  Bond length (R e ) IBr - = 3.025(.01) Å  Electron Affinity (EA) IBr = 2.51(1) eV  Dissociation Energy, D o (I - Br - ) = 0.97(.01) eV

IBr - (CO 2 ) Photoelectron Spectrum Energy IBr - (CO 2 ) IBr(CO 2 ) IBr - + CO 2 IBr + CO 2 EA(IBr)EA(IBr(CO 2 )) D o (IBr - (CO 2 )) D o (IBr(CO 2 )) EA(IBr(CO 2 )) = EA(IBr) + D o (IBr - (CO 2 )) – D o (IBr(CO 2 )) Known Properties: EA(IBr) = 2.51 (.01) eV D o (IBr - (CO 2 )) ~ 0.23 eV D o (IBr(CO 2 ) ~ 0.07 eV EA(IBr(CO 2 )) = 2.67 (.05) eV

Conclusions and Future Directions  R e (IBr - ) = (.01) Ǻ EA (IBr) = 2.51 (1) eV D o (IBr - ) = 0.97 (.01) eV  EA (IBr(CO 2 )) = 2.67 (.05) eV  Investigate the effects of additional CO 2 solvation on IBr -  Pump-Probe photoelectron studies of IBr - (CO 2 ) n  Probing potential energy surfaces and crossings during dissociation/recombination