1. Vibrational Spectroscopy and Theory of Cu+(CH4)n and Ag+(CH4)n (n=1-6)
Abdulkadir Kocak
Muhammad Affawn Ashraf
Ricardo Metz
June 19, 2014

2. M+ + CH4 MCH2+ + H2 M+(CH4) Interest
Some 3rd row transition metal ions can activate methane
Entrance channel complexes
M+ + CH MCH2+ + H2
Spectroscopy structure and bonding
M+(CH4)

3. Open Questions
What is the geometry of M+(CH4)? h2 h3 vs

4. Open Questions
How does the 2nd CH4 bind?
Eclipsed vs Staggered

5. Open Questions
How does the 3rd CH4 bind?
Equilateral
Tee vs

6. Open Questions Structures of larger complexes? 2nd Solvation Shell?
1st Shell vs nd Shell
How does the 4th CH4 bind?
Tetrahedral
Square Planar vs

7. Calculated Binding Energies
CAM-B3LYP functional
Cu: G(3df,3pd)
Ag:aug-cc-pVTZ-PP
C,H: G(3df,3pd)
Vibrational Spectroscopy!
Binding energies (cm-1) for : M+(CH4)n-1-(CH4)  M+(CH4)n-1 + CH4
Metal
n=1
n=2
n=3
n=4
n=5
n=6 Cu
8473
8261
1943
585
335
138 Ag
5450
5385
1903
1214
431
183

8. Apparatus Overview Laser Make Ions Mass Select Spectrometer
Spectroscopy
Laser
Lasers
Metal
rod
Accelerator
Ion optics
Mass gate
Reflectron
Detector
CH4,
He, Ar
Ablation laser
Here is the instrument. I know you are all very familiar with the instrument from the former students but let me overview again briefly. Our experimental setup includes three sections. First make ions; then mass select the narrow range of masses that you are interested in; then get the spectra…
Metal ions are produced by laser ablation to a metal rod. Metal ions then reacted with either H2O or CH4 in carrying gas. Then ions are expanded into vacuum and cooled to rotational temperatures of 10-20K. photodissociated by a second laser which can be an IR OPO/OPA or visible dye laser. Finally photofragment ions are collected at detector at different time than parent ions. Scanning laser and monitoring the fragment ion signal photodissociation spectrum is produced.
If laser is resonance with transition, molecule will absorb…
If the absorbed energy is enough to break any bond in the molecule, it will dissociate…
So two key points here: molecule must absorb, and must dissociate to see fragment…
R. B. Metz, Adv. Chem. Phys. 138, 331 (2008)

9. Characteristic features of η2 complexes
rCu-C: Å
Cu+(CH4)

10. Characteristic features of η3 complexes
rFe-C: Å
Fe+(CH4)
rMn-C: Å
Mn+(CH4)

11. Cu+(CH4)(Ar)2 and Ag+(CH4)
Calculations: B3LYP/ G(3df,3pd)
scaled
Cu+(CH4)(Ar)2
Red shift
(~300 cm-1)
Both η2
rCu-C=2.189 Å
Ag+(CH4)
Calculations:B3LYP/
aug-cc-pVTZ on Ag
and
G(3df,3pd) on C,H
scaled
IRMPD
Silver spectra is IRMPD, therefore broad peaks… Small shift suggest small binding energy, since Ag bigger in size…
rAg-C=2.511 Å
Smaller red shift
(~200 cm-1)
A. Kocak, M. A. Ashraf and R. B. Metz, to be submitted.

12. smaller red shift than Cu
Cu+(CH4)2Ar and Ag+(CH4)2
Cu+(CH4)2Ar
Eclipsed, C2v
rCu-C=2.201 Å
Staggered, Cs
rCu-C=2.184, Å
Erel=0 cm-1
Erel= 72 cm-1
Ag+(CH4)2
Similar red shifts
to n=1
All η2
Staggered, D2d
rAg-C=2.474 Å
Ag+(CH4)2 by IRMPD
smaller red shift than Cu

13. Cu+(CH4)3 and Ag+(CH4)3 Smaller red shifts than n=1,2 Symmetrical
Equilateral, D3h
rCu-C=2.328 Å
Ag+(CH4)3
Ag smaller red shift than Cu; n=3 clearly smaller red shift than n=1,2
Equilateral, D3h
rAg-C=2.628 Å

14. Cu+(CH4)4 and Ag+(CH4)4 Symmetrical All η2 Cu+(CH4)4 Tetrahedral
rCu-C:2.472 Å
Erel=0 cm-1
Trigonal pyramidal Å Å
Erel=19 cm-1
Ag+(CH4)4
Symmetrical
All η2
Tetrahedral
rAg-C=2.746 Å

15. Cu+(CH4)5 and Ag+(CH4)5: 1st shell vs. 2nd shell
Tetrahedral+1CH4
2.459, 2.497, Å (η3)
Erel=17 cm-1
Trigonal bipyramidal
rCu-C: Å
Å (η3)
Erel=0 cm-1
Ag+(CH4)5
Increased intensity near free C-H
Td + 1CH4
Mostly h2
Tetrahedral+1CH4
rAg-C=2.727, 2.732, 2.739, 2.795
4.277Å (η3)
Erel=236 cm-1
Trigonal bipyramidal
rAg-C: 2.804, Å Å
Erel=0 cm-1

16. Cu+(CH4)6 and Ag+(CH4)6: 1st shell vs. 2nd shell
Tetrahedral + 2CH4
Å, Å, Å (η3)
Erel=147 cm-1
Trigonal bipyramidal + 1CH4
rCu-C: Å, Å (η3), Å
Erel=0 cm-1
Ag+(CH4)6
Trigonal bipyramidal+
1 CH4 Å Å Å
Erel=0cm-1
Tetrahedral+2CH4 Å Å
Å (η3)
Erel=82 cm-1
Octahedral Å
Erel=100 cm-1

17. Summary Ground state geometries determined
Since it is d10, molecules choose highly symmetric structures
Cu+ binds 4 CH4, Ag+ binds 6 CH4 for first shell
5th and 6th CH4 are in the second shell and η3 for Cu+
All first shell CH4 are η2 for Ag+

18. Acknowledgements Prof. Metz Abdulkadir Kocak Chris Copeland
Dave Johnston
NSF
Thank you all!
Questions