29 research outputs found
Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols
Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim+][Tf2N?]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim+][Dca?]), are generated by vaporizing ionic liquid submicron aerosol particles for the first time; the vaporized species are investigated by dissociative ionization with tunable vacuum ultraviolet (VUV) light, exhibiting clear intact cations, Emim+ and Bmim+, presumably originating from intact ion pairs. Mass spectra of ion pair vapor from an effusive source of the hypergolic ionic liquid show substantial reactive decomposition due to the internal energy of the molecules emanating from the source. Photoionization efficiency curves in the near threshold ionization region of isolated ion pairs of [Emim+][Tf2N?]ionic liquid vapor are compared for an aerosol source and an effusive source, revealing changes in the appearance energy due to the amount of internal energy in the ion pairs. The aerosol source has a shift to higher threshold energy (~;;0.3 eV), attributed to reduced internal energy of the isolated ion pairs. The method of ionic liquid submicron aerosol particle vaporization, for reactive ionic liquids such as hypergolic species, is a convenient, thermally ?cooler? source of isolated intact ion pairs in the gas phase compared to effusive sources
Prediction of the Size Distributions of Methanol−Ethanol Clusters Detected in VUV Laser/Time-of-Flight Mass Spectrometry
Heats of Vaporization of Room Temperature Ionic Liquids by Tunable Vacuum Ultraviolet Photoionization
Generation of Melamine Polymer Condensates upon Hypergolic Ignition of Dicyanamide Ionic Liquids
Flow-Tube Investigations of Hypergolic Reactions of a Dicyanamide Ionic Liquid Via Tunable Vacuum Ultraviolet Aerosol Mass Spectrometry
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<sup>+</sup>DCA<sup>–</sup>) 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 <i>m</i>/<i>z</i> 42, 43, 44, 67, 85, 126, and higher masses was observed
as a function of HNO<sub>3</sub> 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 <i>m</i>/<i>z</i> 67 signal suggests that the excess gaseous HNO<sub>3</sub> 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