Leonid Sheps

Biography

Leonid (Lenny) Sheps is a Principal Member of the Technical Staff at Sandia National Laboratory. His current research interests include reaction kinetics and dynamics in the gas phase and at gas-liquid interfaces. He leads the Sandia effort within the joint Argonne-Sandia Consortium on Pressure-Dependent Chemistry (CPDC). Prior to joining Sandia, he gained expertise in femtosecond time-resolved studies of reactions and vibrational energy transfer in liquids, as well as excited-state solvation and charge transfer dynamics in molecular clusters.

As part of the DOE/BES-funded Argonne-Sandia CPDC program, Leonid focuses on understanding the interplay between reactivity and collisional energy transfer over broad ranges of temperature and pressure. He designs novel time-resolved experimental methods that utilize photoionization mass spectrometry, broadband cavity-enhanced absorption, and laser-induced fluorescence to characterize and quantify key chemical intermediates and products of complex reaction networks. The experimental results of his studies are closely connected to theoretical kinetics and chemical modeling efforts at Sandia and Argonne National Labs.

In addition, Leonid is developing new approaches to study the chemistry and transport of reactive free radicals and highly oxygenated organic molecules at liquid aerosol and droplet surfaces. This work is done under Laboratory-Directed Research and Development (LDRD) funding from the Advanced Science and Technology program area.

Research Interests: Chemical kinetics and dynamics, photochemistry, electron transfer, reactivity at gas-liquid interfaces.

Google Scholar

Education and Professional Training

Selected Peer-Reviewed Publications

• Kjaersgaard, A., Zádor, J., Zwier, T. S., Shiels, O., Sheps, L., Dimethyl Sulfide Oxidation at 400–545 K: Mass Spectrometric Characterization of Hydroperoxymethyl Thioformate (HPMTF) and Measurement of the CH₃SCH₂O₂→ CH₂SCH₂OOH Rate Coefficient.  J. Phys. Chem. A 2025,129,10452.
• Shiels, O. J., Kjaersgaard, A., Zádor, J., Sheps, L., Low-Temperature Autooxidation of Cyclopentanone and 3-Pentanone: The Critical Role of Competing Radical Chain-Branching and Chain Inhibiting Pathways. Phys. Chem. Chem. Phys. 2025, 27, 23813.
• Sheps, L.; Au, K. New Instrument for time-resolved OH and HO₂ quantification in high-pressure laboratory kinetics studies. J. Phys. Chem. A 2024,128, 3916.
• Demireva, M.; Au, K.; Hansen, N.; Sheps, L. Time-resolved quantification of key species and mechanistic Insights in Low-Temperature Tetrahydrofuran Oxidation.” Phys. Chem. Chem. Phys. 2024, 26, 10357.
• Demireva, M.; Oreluk, J.; Dewyer, A. L.; Zádor, J; Sheps, L. Genetic algorithm optimization of a master equation cyclopentane oxidation model against time-resolved speciation experiments. Comb. Flame 2023, 257, 112506.
• Mulvihill, C. R.; Danilack, A. D.; Goldsmith, C. F.; Demireva, M.; Sheps, L.; Georgievskii, Y.; Elliott, S. N.; Klippenstein, S. J. Non-Boltzmann effects in chain branching and pathway branching for diethyl ether oxidation. Energ. Fuel. 2021, 35, 17890.
• Sheps, L.; Antonov, I.; Au, K. Sensitive mass spectrometer for time-resolved gas-phase chemistry studies at high pressures. J. Phys. Chem. A 2019, 123, 10804.
• Sheps, L.; Rotavera, B.; Eskola, A. J.; Osborn, D. L.; Taatjes, C. A.; Au, K.; Shallcross, D. E.; Khan, M. A. H.; Percival, C. J. The reaction of Criegee intermediate CH₂OO with water dimer: primary products and atmospheric impact. Phys. Chem. Chem. Phys. 2017, 19, 21970.
• Welz, O.; Eskola, A. J.; Sheps, L.; Rotavera, B.; Savee, J. D.; Scheer, A. M.; Osborn, D. L.; Lowe, D.; Murray Booth, A.; Xiao, P. Rate coefficients of C1 and C2 Criegee intermediate reactions with formic and acetic acid near the collision limit: direct kinetics measurements and atmospheric implications. Angew. Chem. 2014, 126, 4635.
• Sheps, L.; Scully, A. M.; Au, K. UV absorption probing of the conformer-dependent reactivity of a Criegee intermediate CH₃CHOO. Phys. Chem. Chem. Phys. 2014, 16, 26701.

Selected Technical Reports

• K. Ramasesha, J. Tross. P. Schrader, L. Sheps, and K. Au, Table-top high photon energy sources for chemical dynamics investigations, Sandia National Laboratories (SNL-CA), Livermore, CA (2021)
• L. Sheps, D. L. Osborn, and N. Hansen, A new approach to fundamental mechanism discovery in polymer upcycling, Sandia National Laboratories (SNL-CA), Livermore, CA (2021)
• L. Sheps. Z. J. Buras, K. Au, J. Zádor, and C. Safta, Rapid assessment of autoignition propensity in novel fules and blends, Sandia National Laboratories (SNL-CA), Livermore, CA (2020)
• L. Sheps and D.W. Chandler, Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics, Sandia National Laboratories (SNL-CA), Livermore, CA (2013)