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

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.

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?

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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)

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