Presentation on theme: "Anomalous behavior observed upon annealing and photodetachment of anionic copper carbonyl clusters in argon matrices Ryan M. Ludwig, Michael E. Goodrich,"— Presentation transcript:
Anomalous behavior observed upon annealing and photodetachment of anionic copper carbonyl clusters in argon matrices Ryan M. Ludwig, Michael E. Goodrich, David T. Moore Chemistry Department, Lehigh University 69 th ISMS, Univ. Illinois Urbana-Champaign June 17, 2014
Counter-ion co-deposition Selective, efficient, general method for trapping ionic chromophores in matrices for spectroscopic study Mass-selected anions co-deposited w/simple counter- cations charge balance throughout deposition Copper carbonyls deposit at 10 K in dark only anions no neutralization from anion-cation collisions vis. photodetachment convert to neutrals Kinetic control over complex formation can we control post-deposition processes (ion-ion interaction)?
Experimental approach simult. deposition of mass-selected anions & counter-cations current-matched, low- energy beams o Cu - & Ar + o 10-60 eV o ~3-4 nA for 4 hr o 0.02% CO/Ar @ 20 K o est. ion abundance ~1:10 6 ions:Ar deposition in dark maximize population of anions annealing and photodetachment steps Ludwig R.; DTM, J. Chem. Phys. 139, 244202 (2013).
Deposition in the dark @ 20 K (0.02% CO) Neutral bands observed upon deposition grow in with annealing new strong peak @ 1745 cm -1 monocarbonyl isomer (?) sharper fine structure than @ 10 K total conversion of anions following vis. irrad. broad “transient” peaks removed by further annealing
Wavelength-dependent photodetachment Broadband 590 nm LED illum. 1 min complete conversion of mono- & dicarbonyls lower photodetachment efficiency for tricarbonyls larger “solvation” complexes resist detachment @ 590 nm remaining peaks neutralized after 1 min w/ 470 nm LED
Wavelength-dependent photodetachment annealing of anions “isomeric” peaks grow in 1 st min @ 590 nm detach mono & dicarbonyl anions “transient peaks” grow in 24 min @ 590 nm detach tricarbonyl anion 1 min @ 470 detach larger complexes higher threshold annealing of neutrals transient peaks “relax” to normal neutral bands
Photodetachment before annealing “transient” monocarbonyl peak absent correlated w/1745 cm -1 peak fewer bands tricarbonyl neutral region generally simpler spectrum annealing anions induces new spectral features annealing neutrals eliminates new spectral features 20K visible irrad. 25K 30K 20K visible irrad. 25K 30K detach e-e- e-e- anneal vertical photodetachment product (!!) anionsneutrals
“High-resolution” spectroscopy High resolution (0.125 cm - 1 ) FTIR fine structure > 20 resolved peaks in region of anionic tricarbonyl also less structure in neutral region when detach precedes anneal Assignment: reproducible, (meta)stable matrix “sites” long-range pertubations from cations? 30 K anneal vis.
Conclusions Neutralization observed during “dark” deposition at 20 K cation-anion electron transfer neutralization (?) anneal detach anneal cycle gives stepwise production of new anionic & neutral species kinetic trapping of vertical detachment product (?) high-resolution (0.125 cm -1 ) spectra reveals rich fine structure of instrument-limited lines perturbation of vibrational/electronic levels by electric field of adjacent cations? GOOD THEORY IS DESPERATELY NEEDED!!!
Acknowledgements Moore Group Angela Smith Nina Finamore Ryan Ludwig Mike Goodrich Becky Klimas (M.S.) Alex Hunter (M.S.) undergraduates Edric Miro Gavin Erin Hassell Tony Thompson Christina Marrone Chris Caputo Nick Greybush Ankit Pokherel Nick Voellinger Funding NSF CAREER Award Lehigh Univ. (Start-Up)