1. Vibrational Predissociation of the Methanol Dimer
Ruomu Jiang
Edwin L. Sibert
University of Wisconsin-Madison
International Symposium on Molecular Spectroscopy
62nd Meeting - - TF12 June 19, 2007

2. Vibrational Predissociation (VP)
A weakly bound complex
Photon
Vibrational energy is converted into translational energy
Dissociation Coordinate

3. VP in the Condensed Phase
Frequency (cm-1)
Intensity
The OH stretch IR spectrum
Woutersen et al. J. Chem. Phys. 107, 1483 (1997)
Alcohol oligomers in CCl4
Experimental timescales:
Graener lab, 1989, 5 ps
Laenen lab, , , 2 ps
Bakker lab, 1997, ps
Fayers lab, 2002, 0.2, 2 ps
Theoretical:
Hynes “lab”, 1993, 12 ps
Staib “lab”, 1998, 12 ns
Hydrogen bond (Hbond) energy ~ 2000 cm-1

4. 3-D Methanol Dimer Model
Calculated Normal Frequencies (cm-1)
Dimer
Monomer
Donor OH Stretch
3674
3839
Hbond Stretch
190
---
COH Bend
1416
1353
CO Stretch
1072
1046
Donor OH Torsion
710
311

5. 2-D Potential Energy Surface
Potential calculated at the B3LYP/6-31++g(d,p) level of theory
Torsion (°)
Other degrees of freedom adiabatically optimized
Hbond Stretch (Å)

6. Fermi’s Golden Rule Approach
Ψquasi : quasibound
Ψconti : continuum
Ψquasi
(1,0)
Fermi’s Golden Rule (FGR):
1 / lifetime ~ <Ψquasi|Vcoupling|Ψconti>2
Ψconti
OH Stretch
Etrans
(0,0)
Vibrational Self-Consistent Field basis:
Step 1, iteratively solve for 1-D OH stretch and torsion wavefunctions. Step 2, form product basis
Torsion
Hbond Stretch (Å)

7. Predissociation lifetimes
(1,0)
~ years
(0,0)
(1,0)
~ seconds
(0,3)
Energy (cm-1)
(1,0)
11 ns
(0,6)
(1,0)
13 ps
(0,12)
Hbond Stretch (Å)

8. Comparison with Close Coupling Results
Predissociation lifetimes (ps)
Solve the close-coupling equations with the R-matrix propagation method
Extract the resonance lifetime from the scattering phase shift
νHbond 1 2 CC 25 24 80
FGR 13 11 22 29 33 95 21 37 40 13 17 11 CC
Scaling the frequency shift of the OH stretch to 150%
CH3OH
CH3OD

9. Summary
The vibrational SCF basis proves suitable for the FGR calculation of the system
Purely vibrational to translational energy transfer is extremely slow
VP through torsional excitation is very efficient
Future Work
MD simulation of a methanol dimer in CCl4 solvent
VP as due to curve crossing between OH stretch excited state and highly excited torsional states

10. Acknowledgement Jayashree Nagesh Patrick McElfresh George Barnes
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Jayashree Nagesh
Patrick McElfresh
George Barnes
Sai Ramesh
Edwin Sibert