The Low Energy Unimolecular Reaction Rate Constants for the Gas Phase Ni+ Mediated Dissociation of

the C-C s-bond in Acetone.

NiAc+ → NiCO+ + C2H6

Vanessa Castleberry and Darrin Bellert, PhD Baylor University

Our Instrument

A Parent Mass Spectrum

Tuning the Hemispherical Energy Analyzer

Scheme

Kinetic Studies

How we make our measurements

0 10 20 30 40 50 60Time (ms)

0kt

tA A e

How We Interpret the Data

C – C s-bond activation occursIn Acetone photolysis of 2 C-C s-bond* Acetone dissociation catalyzed by Ni+ in

our studies

152 000cm 116 000cm

* Woodbridge, et. al., JPC, 1988, 92(19)

Rate Constants for Different Energies

Internal energy (cm-1) k(E)(ms-1)

18800 0.113 ± 0.005

18000 0.087 ± 0.003

16400 0.059 ± 0.002

16100 0.058 ± 0.003

15600 0.055 ± 0.003

Which Step is Rate Limiting??

2 Probable Candidates

But, these results can’t reveal which step is rate limiting

Comparison studies using the isotope effect: d6 - Acetone

Kinetic Isotope Effect

Apparent Rate Limiting Step?

Acknowledgements

• Bellert group:– Ivanna Laboren– Otsmar Villarroel– Jason Dee– Sarah Frey (enthusiastic undergraduate)

• Baylor University Department of Chemistry and Biochemistry

Questions?