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

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

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, 1997-99, 0.45-0.6, 2 ps Bakker lab, 1997, 0.25-0.9 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

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

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)

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)

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)

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

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

Acknowledgement Jayashree Nagesh Patrick McElfresh George Barnes 4’0” 5’0” 5’6” 4’6” 6’0” 6’6” 4’0” 5’0” 5’6” 4’6” 6’0” 6’6” Jayashree Nagesh Patrick McElfresh George Barnes Sai Ramesh Edwin Sibert