EVALUATION OF THE EXOTHERMICITY OF THE CHEMI-IONIZATION REACTION Sm + O SmO + + e Richard M Cox, JungSoo Kim, P. B. Armentrout, Department of Chemistry, University of Utah, Salt Lake City, UT Joshua H. Bartlett, Robert A. VanGundy, Michael C. Heaven, Department of Chemistry, Emory University, Atlanta, GA Joshua J. Melko, University of North Florida, Department of Chemistry, Jacksonville, FL Shaun G. Ard, Nicholas S. Shuman, and Albert A. Viggiano, Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117 2 Image from cpi.com Radio Wave Propagation Effects Problem: How to mitigate scintillation effects on radio wave propagation Solution: Use enhanced plasma densities to overwhelm natural instabilities 3 Metal Oxide Space Cloud (2013, Nov 2014) Discharge Ports SmSm SmSm SmSm SmSm SmSm SmSm SmSm SmSm - - SmSm SmO + Expelled Metal Vapor Quickly Reacts with Ambient Oxygen And Spontaneously Ionizes To form dense long-lived plasma Terrier-Improved Orion Sounding Rocket Thermite Release Canisters Actual burst-disc release canister A few kg of metal, vaporized, ionized, and dispersed, predicted to create enhanced ionosphere over areas up to 100 km O O O O O O O O O O O O O O O O O 4 Chemical releases of Sm in the ionosphere (background) AF Goal: Create increased plasma density in ionosphere to effect radiowaves Experiment: Metal Oxide Space Cloud (MOSC) Release Sm at 200 km; Sm + O (ambient) SmO + + e - exothermic if D(SmO) > IE(SmO) Problems: Characterization predictions wrong - Different shape, color and orientation - e - density 10x lower than predicted Solution: Re-measure chemistry Search for other candidates (green) 5 Chemical releases of Sm in the ionosphere (solution) Exothermicity of Sm + O SmO + + e - was thought to be 0.4 eV, but this is now in question. AFRL Measure thermal reactions of interest Sm + will be oxidized quickly SmO + is unreactive University of Utah measure Sm + -O bond dissociation energy (BDE) Emory University measure SmO ionization energy (IE) 6 Variable Temperature Selected Ion Flow Tube VT- SIFT 7 Reactant Gas Inlets Venturi Inlet Source Gas Variable Temperature Selected Ion Flow Tube VT- SIFT Fe + FeO + Fe + FeO + He R R R R R P+P+ P+P+ P+P+ Electron Impact Source He 8 Measured ( T 300k): Sm + + O 2 SmO + + O k(300) = 2.8e-10 cm 3 s -1 k T -.1 Sm + + N 2 O SmO + + N 2 k(300) = 1.3e-10 cm 3 s -1 k T -.4 Sm + + NO No Rxn Sm + + C 2 H 4 No Rxn Sm + + CO 2 No Rxn Sm + + SO 2 SmO + + SO k(300) = 4e-10 cm 3 s -1 k T -.6 Sm + + NO 2 SmO + + NO k(300) = 6e-10 cm 3 s -1 k T -.6 SmO + + N 2 O + He SmO(N 2 O) + + He k ter = (1.2e-28 cm 6 s -1 ) SmO + + SO 2 + He SmO(SO 2 ) + + He k ter = (1.2e-27 cm 6 s -1 ) SmO + + CO 2 + He SmO(CO 2 ) + + He k ter = (1.1e-28 cm 6 s -1 ) SmO + + NO 2 + He SmO(NO 2 ) + + He k ter = (2.1e-27 cm 6 s -1 ) Ion Evolution? Are the ions in the plasma, (SmO + and possibly Sm + from photoionization) evolving into species where recombination is prevalent? SmO + was not found to react with any of the most common oxygen donors to form SmO 5.66 eV k rxn /k col = 0.25 Reaction with SO 2 Collision-induced dissociation with Xe Collision-induced dissociation with Xe & O 2 Measurement of the IE for SmO. Emory University Multi-Photon Ionization Processes M M* M + + e - hv 1 hv 2 hv 1 hv 2 REMPIZEKE PIEMATI Pulsed electric field LIF Spectrum for SmO, showing the [16.6]1-X0 - origin band T rot =10 K SmO + X0 - [16.6]1 Photoionization efficiency curve for ionization of SmO via the [16.6]1 state SmO ionization threshold from two-color PFI-ZEKE D 0 (Sm + -O) = 5.62 0.15 eVReaction with CO 5.67 0.16 eVCID with Xe 5.78 0.09 eVCID with O 0.07 eVweighted average 5.78 0.17 eVD(SmO) & IE(SmO) 5.97 0.20 eVLiterature Sm + O SmO + + e H = IE(Sm) D 0 (SmO + ) = = 0.07 eV Sm + O SmO + + e H = IE(SmO) D 0 (SmO) = 5.88 = 0.17 eV This result agrees with atmospheric observations. New Thermochemistry Key result for the chemical release experiment: Exothermicity of Sm + O SmO + + e - is 0.1 rather than 0.4 eV Implies that reverse reaction occurs often: SmO + + e - Sm + O (red distribution vs blue) leading to plasma loss Consistent with MOSC experiment Search for other candidates (green)