Kinetic and Thermodynamic Studies of Gaseous Metallo- Organic Complexes Jason Dee, Darrin Bellert Baylor University June 25, 2009

Outline What we do What we do How we do it How we do it What we learn from it What we learn from it

What we do A major goal of our research is to obtain rate constants of unimolecular decomposition of mass- selected metallo-organic ionic complexes via laser- driven photodissociation A major goal of our research is to obtain rate constants of unimolecular decomposition of mass- selected metallo-organic ionic complexes via laser- driven photodissociation Investigate bond rupture dynamics and conditions required to open various dissociative pathways in metal catalyzed systems Investigate bond rupture dynamics and conditions required to open various dissociative pathways in metal catalyzed systems

Custom built molecular beam apparatus Custom built molecular beam apparatus Orthogonal Extraction Orthogonal Extraction Hemispherical energy analyzer tuned to transmit the full kinetic energy of molecular beam Hemispherical energy analyzer tuned to transmit the full kinetic energy of molecular beam Voltage tuned to transmit solely “daughter” ions produced following photodissociation Voltage tuned to transmit solely “daughter” ions produced following photodissociation

Mass Spectra of Ni + Acetaldehyde Clusters Generated

Daughter fragments produced through photodissociation of Ni + Acetaldehyde

Possible mechanism for decarbonylation of Ni + Acetaldehyde Left trace ~ Ni + isertion into a C-H bond followed by a methide shift Left trace ~ Ni + isertion into a C-H bond followed by a methide shift Right trace ~ Ni + insertion into a C-C bond followed by a hydride shift Right trace ~ Ni + insertion into a C-C bond followed by a hydride shift

How we measure rate constants Intersect molecular beam with laser before extraction Intersect molecular beam with laser before extraction Sector to transmit only ions with appropriate “daughter” kinetic energy Sector to transmit only ions with appropriate “daughter” kinetic energy Parent complex must dissociate after exiting the acceleration grid Parent complex must dissociate after exiting the acceleration grid

What we were anticipating… Laser must have sufficient energy to couple to dissociative state Laser must have sufficient energy to couple to dissociative state There is a time delay after laser excitation before dissociative fragments are detected There is a time delay after laser excitation before dissociative fragments are detected Plot ln [Int] vs time to obtain rate constant Plot ln [Int] vs time to obtain rate constant Don’t draw your line before plotting your points…

What we are actually acquiring A t =A 0 e -kT

Ni + Ald → Ni + CO Two representative plots of decarbonylation of Ni+Acetaldehyde Two representative plots of decarbonylation of Ni+Acetaldehyde Top~18000 cm -1 Top~18000 cm -1 Bottom~16,000 cm -1 Bottom~16,000 cm -1 Two Different Pathways Observed with different rate constants Two Different Pathways Observed with different rate constants

Kinetic Scans of Ketones Rate constants acquired after deuterization of Acetone were ~5x greater than those of normal acetone Rate constants acquired after deuterization of Acetone were ~5x greater than those of normal acetone Vanessa Castleberry’s talk on Friday (FB05) Vanessa Castleberry’s talk on Friday (FB05)

Comparing Ni + Ald to Ni + Ac Internal energy (cm -1 ) k(E) (µs -1 ) ± ± ± ± ± C-C insertionC-H insertion Internal energy (cm -1 ) k(E) (µs -1 ) 18, ± ± , ± ± , ± ± , ± ± , ± ± , ± ± , Ni + Ac →Ni + CO Ni + Ald →Ni + CO

What we learned from it Molecular Migration appears to be rate-limiting step in simple ketones Molecular Migration appears to be rate-limiting step in simple ketones From the Ni + Ald studies From the Ni + Ald studies Ni + insertion into either a C-H or C-C sigma bond is possible Ni + insertion into either a C-H or C-C sigma bond is possible Isomerization Step appears to be rate limiting step though further studies are needed Isomerization Step appears to be rate limiting step though further studies are needed At lower energies, C-C insertion followed by a hydride shift appears to predominate At lower energies, C-C insertion followed by a hydride shift appears to predominate Rate Constants dependent on energy of photon beam Rate Constants dependent on energy of photon beam

Acknowldgements Baylor University Baylor University Petroleum Research Fund (PRF) Petroleum Research Fund (PRF) Dr. Darrin Bellert Dr. Darrin Bellert Bellert Research Group Bellert Research Group Vanessa Castleberry Vanessa Castleberry Otsmar Villareal Otsmar Villareal Ivanna Laboren Ivanna Laboren Sarah Frey Sarah Frey

Any Questions? Or post-doc positions… Or post-doc positions…

How cold is our molecular beam? Fit experimental data to Maxwell-Boltzmann distribution of velocities Fit experimental data to Maxwell-Boltzmann distribution of velocities Top~Pure He expansion with Ni Top~Pure He expansion with Ni T = 12.2 K T = 12.2 K M = 8.6 M = 8.6 Bottom~Acetaldehyde doped He expansion Bottom~Acetaldehyde doped He expansion T = 0.32 K T = 0.32 K M = 63 M = 63