The Neumark Group

Department of Chemistry, University of California Berkeley
and Chemical Science Division, Lawrence Berkeley National Laboratory

Slow photoelectron velocity-map imaging spectroscopy

Fast beam translational spectroscopy

Femtosecond Time-resolved photoelectron imaging

Molecular beam photodissociation dynamics

Spectroscopy and dynamics in helium droplets

Attosecond spectroscopy

Spectroscopy and dynamics in liquid microjets

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Molecular Beam Photodissociation Dynamics


Photofragment translational spectroscopy is used to study the photodissociation dynamics of reactive free radicals. Molecules in a molecular beam absorb UV photons from an excimer laser pulse and dissociate into photofragments that scatter away from the molecular beam. These photoproducts are then characterized as a function of scattering angle using time of flight mass spectrometry with a rotatable detector. A tunable electron impact ionizer enables isomer-specific identification by measurement of ionization efficiency curves.

We are interested in constructing translational energy distributions, P(ET), for the photofragments, and determining product branching ratios when multiple dissociation pathways exist. The numerical details of these P(ET) and product branching ratios can be compared to statistical theories of unimolecular dissociation. These data allow us to infer the specific mechanisms that lead to each dissociation pathway, such as whether dissociation occurs on the ground electronic state or on some excited state.

Molecules studied:

Cyclopentadienyl radical (in progress!)

Fulvenallenyl radical


Methyl perthiyl radical

Benzyl radical

Project members:

Isaac Ramphal

Chin Lee

Recent publications:

♦ "Photodissociation of the cyclopentadienyl radical at 248 nm" M. Shapero, I. A. Ramphal, D. M. Neumark, J. Phys. Chem. A 122, 4265 (2018). pdf

♦ "Photodissociation dynamics of fulvenallene and the fulvenallenyl radical at 248 and 193 nm" I. A. Ramphal, M. Shapero, C. Haibach-Morris, D. M. Neumark, Phys. Chem. Chem. Phys. 19, 29305 (2017). pdf

♦ "Production and Photodissociation of the Methyl Perthiyl Radical" N. C. Cole-Filipiak, M. Shapero, C. Haibach-Morris, D. M. Neumark, J. Phys. Chem. A 120, 4818 (2016). pdf

♦ "Benzyl Radical Photodissociation Dynamics at 248 nm" M. Shapero, N. C. Cole-Filipiak, C. Haibach-Morris, D. M. Neumark, J. Phys. Chem. A 119, 12349 (2015). pdf