Controlled Neutralization of Anions in Cryogenic Matrices by Photodetachment

Ryan M. Ludwig, David T. Moore

Chemistry Department, Lehigh UniversityBethlehem, PA 18015

2

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

3

10K Deposition

1 2 3 123

• 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

4

10K Deposition

1 2 3 123

(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

5

Mixed Isotope

• 12CO:13CO 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 D3h symmetry

30K

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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

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0.125cm-1 Resolution

• Irradiation during deposition • Taken after 20K

annealing• Peaks are

intrinsically broad• Consistent with

inhomogeneous broadening

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“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

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Photodetachment

• Dicarbonyl species first to photodetach

• Followed by monocarbonyl

• Tricarbonyl last to photodetach

• Trend follows gas phase valuesSpecies Energy (eV)

Cu- 1.23

Cu(CO)2- 0.95

Cu(CO)3- 1.02

Stanzel, J.; Aziz, E. F.; Neeb, M.; Eberhardt, W. Collect. Czech. Chem. Commun. 2007, 72, 1-14.

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Conclusions

• Formation and stabilization of anionic metal compounds is possible with counter-ion deposition

• Photodetachment leads to neutralization of anionic species

Acknowledgements• $$ NSF CHE-0955637• Lehigh University

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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