Lauren Simitz

All Publications

• Experimental Measurement of the Rate Coefficient for OCS + M, with M = Ar, He, N2, CO2 in a Shock Tube Using Laser Absorption Spectroscopy. The journal of physical chemistry. A Panda, A., Biswas, P. A., Simitz, L. V., Streicher, J. W., Strand, C. L., Hanson, R. K. 2026

  Abstract

  A comprehensive understanding of sulfur chemistry is crucial for the characterization and modeling of planetary atmospheres. The unimolecular decomposition of carbonyl sulfide (OCS + M = CO + S + M) is a critical reaction for the development of accurate photochemical models. In this study, we employ laser absorption spectroscopy (LAS)-based diagnostics in a shock tube to investigate the rate coefficient of OCS decomposition. Sensitive and interference-free diagnostics were developed to monitor OCS depletion at 2070.858 cm-1 and CO formation at 2115.628 cm-1. The reaction rate coefficient of OCS decomposition was measured over a temperature range of 1800-2500 K. This work represents the first experimental determination of OCS decomposition rates in bath gases pertinent to several planetary environments (i.e., He, N2, and CO2). Additionally, we characterize the pressure dependence of the reaction rate through measurements at 1, 2, and 8 atm. The rate constant measured at 2 atm for argon, k1,Ar, aligns with previous studies and is given by k1,Ar = 3.48 × 10-10 exp (-257kJ/RT) cm3 molecule-1 s-1. The relative Chaperone efficiencies at 2 atm were determined as k1,He/k1,Ar = 2.68, k1,N2/k1,Ar = 1.85, and k1,CO2/k1,Ar = 3.67 through our experiments. Our results provide new insights into OCS kinetics, marking the first systematic study of its pressure-dependent behavior in exoplanetary-relevant conditions. These findings, underscored by low experimental uncertainties (±9.0% for k1,Ar, ±12% for k1,He, ±18% for k1,N2, and ±24% for k1,CO2) reflect high-quality, repeatable measurements that will support sulfur chemistry atmospheric modeling and enhance the interpretation of spectroscopic observations from missions such as the James Webb Space Telescope (JWST).

  View details for DOI 10.1021/acs.jpca.5c07383

  View details for PubMedID 41608828

• Experimental and numerical investigation of flame stabilization and pollutant formation in matrix stabilized ammonia-hydrogen combustion COMBUSTION AND FLAME Vignat, G., Zirwes, T., Toro, E. R., Younes, K., Boigne, E., Muhunthan, P., Simitz, L., Trimis, D., Ihme, M. 2023; 250

  View details for DOI 10.1016/j.combustflame.2023.112642

  View details for Web of Science ID 000945070400001

• Evaluating the Rheo-electric Performance of Aqueous Suspensions of Oxidized Carbon Black. Journal of colloid and interface science Ramos, P. Z., Call, C. C., Simitz, L. V., Richards, J. J. 2022; 634: 379-387

  Abstract

  HYPOTHESIS: The macroscopic properties of carbon black suspensions are primarily determined by the agglomerate microstructure built of primary aggregates. Conferring colloidal stability in aqueous carbon black suspensions should thus have a drastic impact on their viscosity and conductivity.EXPERIMENTS: Carbon black was treated with strong acids following a wet oxidation procedure. An analysis of the resulting particle surface chemistry and electrophoretic mobility was performed in evaluating colloidal stability. Changes in suspension microstructure due to oxidation were observed using small-angle X-ray scattering. Utilizing rheo-electric measurements, the evolution of the viscosity and conductivity of the carbon black suspensions as a function of shear rate and carbon content was thoroughly studied.FINDINGS: The carboxyl groups installed on the carbon black surface through oxidation increased the surface charge density and enhanced repulsive interactions. Electrostatic stability inhibited the formation of the large-scale agglomerates in favor of the stable primary aggregates in suspension. While shear thinning, suspension conductivities were found to be weakly dependent on the shear intensity regardless of the carbon content. Most importantly, aqueous carbon black suspensions formulated from electrostatically repulsive primary aggregates displayed a smaller rise in conductivity with carbon content compared to those formulated from attractive agglomerates.

  View details for DOI 10.1016/j.jcis.2022.12.017

  View details for PubMedID 36542968