Flow-Tube Investigations of Hypergolic Reactions of a Dicyanamide Ionic Liquid Via Tunable Vacuum Ultraviolet Aerosol Mass Spectrometry

Steven D Chambreau; Christine J Koh; Denisia M Popolan-Vaida; Christopher J Gallegos; Justin B Hooper; Dmitry Bedrov; Ghanshyam L Vaghjiani; Stephen R Leone

doi:10.1021/acs.jpca.6b06289

Flow-Tube Investigations of Hypergolic Reactions of a Dicyanamide Ionic Liquid Via Tunable Vacuum Ultraviolet Aerosol Mass Spectrometry

J Phys Chem A. 2016 Oct 20;120(41):8011-8023. doi: 10.1021/acs.jpca.6b06289. Epub 2016 Oct 7.

Authors

Steven D Chambreau¹, Christine J Koh², Denisia M Popolan-Vaida^{2

3}, Christopher J Gallegos⁴, Justin B Hooper^{5

6}, Dmitry Bedrov^{5

6}, Ghanshyam L Vaghjiani⁴, Stephen R Leone^{2

3}

Affiliations

¹ ERC, Inc., Edwards Air Force Base, California 93524, United States.
² Departments of Chemistry and Physics, University of California , Berkeley, California 94720, United States.
³ Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
⁴ Propellants Branch, Rocket Propulsion Division, Aerospace Systems Directorate, Air Force Research Laboratory, AFRL/RQRP, Edwards Air Force Base, California, 93524, United States.
⁵ Department of Materials Science and Engineering, University of Utah , 122 South Central Campus Drive, Room 304, Salt Lake City, Utah 84112, United States.
⁶ Wasatch Molecular Inc., 825 North 300 West, Salt Lake City, Utah 84103, United States.

PMID: 27657880
DOI: 10.1021/acs.jpca.6b06289

Abstract

The unusually high heats of vaporization of room-temperature ionic liquids (RTILs) complicate the utilization of thermal evaporation to study ionic liquid reactivity. Although effusion of RTILs into a reaction flow-tube or mass spectrometer is possible, competition between vaporization and thermal decomposition of the RTIL can greatly increase the complexity of the observed reaction products. In order to investigate the reaction kinetics of a hypergolic RTIL, 1-butyl-3-methylimidazolium dicyanamide (BMIM⁺DCA^-) was aerosolized and reacted with gaseous nitric acid, and the products were monitored via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry at the Chemical Dynamics Beamline 9.0.2 at the Advanced Light Source. Reaction product formation at m/z 42, 43, 44, 67, 85, 126, and higher masses was observed as a function of HNO₃ exposure. The identities of the product species were assigned to the masses on the basis of their ionization energies. The observed exposure profile of the m/z 67 signal suggests that the excess gaseous HNO₃ initiates rapid reactions near the surface of the RTIL aerosol. Nonreactive molecular dynamics simulations support this observation, suggesting that diffusion within the particle may be a limiting step. The mechanism is consistent with previous reports that nitric acid forms protonated dicyanamide species in the first step of the reaction.