Controlled Neutralization of Anions in Cryogenic Matrices by Photodetachment Ryan M. Ludwig, David T. Moore Chemistry Department, Lehigh University Bethlehem, PA 18015

Introduction Using matrix isolation for study of ions Need charge balance Controlled deposition of counter-ions 2 hour dep -10eV Cu - 60eV Ar + 2% CO in Ar 27 mmol/hour 10K Anionic Copper Carbonyl 2

10K Deposition Upon deposition both anionic and neutrals formed How are neutrals formed? No direct line of site from source Ion recombination Photodetachment n=1 n=2 n=3 3

10K Deposition (CO) 2 - n=1 n=2 n=3 Careful control of ambient light Only anionic peaks observed! Irradiation Population transfer from anionic to neutral Photo-electrons flow through CB of solid argon ~1eV above vacuum level New peak at 1774 cm -1 4

Mixed Isotope 12 CO: 13 CO 50:50 mix Typical 1:1 for monocarbonyl 1:2:1 for dicarbonyl Same for new peak Broad shape for 5:3:3:5 for tricarbonyl with D 3h symmetry 30K 5

Irradiation during Deposition Only neutral copper species upon deposition Spectra qualitatively the same as deposition followed by photodetachment Neutralization event likely occurs after complex formation 6

0.125cm -1 Resolution Irradiation during deposition Taken after 20K annealing Peaks are intrinsically broad Consistent with inhomogeneous broadening 7

“Thermal” Neutralization? 15K annealing  very small neutral peaks for dicarbonyl and tricarbonyl (due to free Cu - centers) Higher annealing  loss of matrix Low intensity light  mono- and di-carbonyl neutralize first Full intensity light  complete neutralization 8

Photodetachment Dicarbonyl species first to photodetach Followed by monocarbonyl Tricarbonyl last to photodetach Trend follows gas phase values SpeciesEnergy (eV) Cu Cu(CO) Cu(CO) Stanzel, J.; Aziz, E. F.; Neeb, M.; Eberhardt, W. Collect. Czech. Chem. Commun. 2007, 72,

Conclusions Formation and stabilization of anionic metal compounds is possible with counter-ion deposition Photodetachment leads to neutralization of anionic species Acknowledgements $$ NSF CHE Lehigh University 10

0.5% CO Stoichiometry shifted to lower coordination Annealing No neutral peaks Broad feature anneals in Broad feature anneals out Irradiation Dicarbonyl grows in Sharp features arise from tricarbonyl 11