1. PROBING THE MOLECULAR DYNAMICS OF A Cu(CD3OD) CLUSTER WITH
PHOTODETACHMENT-PHOTOIONIZATION
SPECTROSCOPY
jack barbera
JILA/University of Colorado: Vladimir Dribinski
Carl Lineberger
Ohio State University: Samantha Horvath
Anne McCoy

2. The Goal Physical Chemists strive to understand the fundamentals
of the world around them.
Dynamics within solvated
ion systems
The talk looks long to me, and this might be a figure to drop.

3. The Problem Many chemical reactions take place in solution
The complexity of bulk solvation hinders extraction of fundamental dynamics
18mL H2O = 1 mole = 1023 molecules
Dynamics take place in ~1 ps (1X10-12 s)
Each water molecule is different
How do we extract dynamical information?

4. Our Solution
The size-selected gas phase cluster provides a simplified environment allowing for detailed investigation both experimentally and theoretically
Stepwise addition of solvent molecules allows determination of individual solvent interaction and perturbation of system

5. Photodetachment-Photoionization Spectroscopy
ion-dipole interaction − δ+ δ-
Mass select specific cluster size in TOF
X −(L)
Anion cluster provides initial geometry

6. Photodetachment-Photoionization Spectroscopy
initial state prep − δ+ δ-
X −(L)
electron
Photodetach e- from metal to produce neutral cluster

7. Photodetachment-Photoionization Spectroscopy
initial state prep
Energy
neutral
anion R Δt
Time evolving
complex δ- δ+ δ+ δ- − δ+ δ-
X −(L)
electron
Neutral initially at anion geometry ---- undergoes dynamics

8. Photodetachment-Photoionization Spectroscopy
hv3
ionization
hv2 (tunable)
structure probe
hν1
photodetachment
initial state prep
Energy Δt
neutral δ+ δ- δ- δ+
anion −
Mass select ONLY this size cluster in TOF
Time evolving
complex δ+ δ-
X −(L)
electron
electron R
Probe pulses delayed from detachment pulse

9. Photodetachment-Photoionization Spectroscopy
hv3
ionization
hv2 (tunable)
structure probe + δ- δ+
hν1
photodetachment
initial state prep
Detect X+, X+(L)
as a function
of Δt
Energy Δt
neutral δ+ δ- δ- δ+
anion + −
Time evolving
complex δ+ δ-
X −(L)
electron
electron R
Cation formation allows secondary mass selection

10. System under investigation−
Cu−(CD3OD)
VDE = 1.42 eV
Cu°(CD3OD)
VIE = 8.12 eV
All calculations performed using: MP2/(aug-SDB aug-cc-pVTZ)

11. Cu(CD3OD) Spectroscopy
267 nm
Cu*
2P1/2,3/2
327 nm
Cu°
2S1/2
398 nm
Cu- 1S

12. Time-Dependent Signal
Neutral cluster population decays after electron photodetachment
Cu+(CD3OD)

13. Time-Dependent Signal
Cu+
Neutral copper population increases
after electron photodetachment
Cu+(CD3OD)

14. Time-Dependent Signal
Cu+
Single Exponential Fit
Cu+(CD3OD)

15. Time-Dependent Signal
Cu+
Double Exponential Fit
t1 = 3 ps
t2 = 30 ps
Cu+(CD3OD)

16. Comparison to Cu(H2O) study
Similar anion and neutral structure
Comparable detachment and ionization energies
Slightly different dissociation times t1
1 ps t2
10 ps t3
100 ps tA
3 ps tB
30 ps
Cu−(H2O) −
Cu(H2O)
Cu(H2O)
Cu(CD3OD)
M. Taylor, F. Muntean, A.B. McCoy, and W.C. Lineberger; JCP, 2004

17. Cu(H2O) time dependence
1 ps component
direct dissociation upon photodetachment
10 ps component
coupling of intermolecular water rotation (angle θ) to Cu-O stretch component
100 ps component
coupling of intramolecular water vibration (angle Φ) to Cu-O stretch component θ Φ
M. Taylor, F. Muntean, A.B. McCoy, and W.C. Lineberger; JCP, 2004

18. Radial Potential Energy Curves
Vertical Detachment:
Neutral at ANION Geometry
Neutral
Cu(CD3OD)
Cu(H2O)
Anion

19. Radial Potential Energy Curves
Cu(H2O) well depth:
~300 cm-1
Cu(H2O) neutral
at anion geometry
Cu(CD3OD) well depth:
~650 cm-1
No Direct Dissociation Component: t1 ≠ tA
Cu(CD3OD) neutral
at anion geometry
Neutral at ANION geometry

20. tA (3 ps) Time Component
Due to coupling of angular rotation (θ) into Cu-O stretch component
Rotational barrier of ~150 cm-1
Average KE of 116 cm-1 (200K)
Leads to faster coupling than equivalent motion in Cu(H2O), 10 ps θ

21. tB (30 ps) Time Component
Due to coupling of methyl rotation (Ω) into Cu-O stretch component
Many vibrational levels populated at 200K
Methyl rotor accelerates IVR
Faster coupling than H-bend in Cu(H2O), 100 ps Ω

22. Summary/Conclusions
Electron photodetachment produces an ensemble of neutral Cu(CD3OD) complexes which undergo large-amplitude solvent reorientation and dissociation
Time evolution of the daughter fragments indicates both slow (3 ps) and longer (30 ps) dissociation time scales of parent neutral
Deep well present upon electron detachment of Cu−(CD3OD) prevents direct dissociation observed in Cu(H2O) study
Strong coupling of intermolecular rotations to Cu-O stretch leads to faster dissociation times for Cu(CD3OD) compared to Cu(H2O)

23. fin
THANK YOU