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

69th ISMS, Univ. Illinois Urbana-ChampaignJune 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 ~1:106 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

1750 1800 1850 1900 1950 2000 20500.00

0.01

0.02

0.03

0.04

0.05

0.06

anneal to 35 K

anneal to 30 K

1 min 470 nm

24 min 590 nm

1 min 590 nm

Ab

sorb

an

ce

wavenumber (cm-1)

anneal to 30 K

• annealing of anions “isomeric” peaks grow in

• 1st 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

visibleirrad.

25K

30K

1750 1800 1850 1900 1950 2000 20500.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

D

B

C

Abs

orba

nce

(x10

-2 O

.D.)

Wavenumber (cm-1)

A20K

visibleirrad.

25K

30Kdetach

e-

detach

e-

anneal anneal

vertical photodetachment product (!!)

anions neutrals

“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?

1800 1850

0.000

0.005

0.010

Ab

sorb

an

ce

Wavenumber (cm-1)

30 K anneal

vis.

1900 2000 2050

0.00

0.02

Abs

orba

nce

Wavenumber (cm-1)

1890 1980 1995 20100.0

0.2

0.4

0.6

0.8

1.0

Abs

orba

nce

(x10

-2 O

.D.)

Wavenumber (cm-1)

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)