Heats of vaporization of room temperature ionic liquids by tunable vacuum ultraviolet photoionization

The heats of vaporization of the room temperature ionic liquids (RTILs) N-butyl-N-methylpyrrolidinium bistrifluorosulfonylimide, N-butyl-N-methylpyrrolidinium dicyanamide, and 1-butyl-3-methylimidazolium dicyanamide are determined using a heated effusive vapor source in conjunction with single photon ionization by a tunable vacuum ultraviolet synchrotron source. The relative gas phase ionic liquid vapor densities in the effusive beam are monitored by clearly distinguished dissociative photoionization processes via a time-of-flight mass spectrometer at a tunable vacuum ultraviolet beamline 9.0.2.3 (Chemical Dynamics Beamline) at the Advanced Light Source synchrotron facility. Resulting in relatively few assumptions, through the analysis of both parent cations and fragment cations, the heat of vaporization of N-butyl-N-methylpyrrolidinium bistrifluorosulfonylimide is determined to be Delta Hvap(298.15 K) = 195+-19 kJ mol-1. The observed heats of vaporization of 1-butyl-3-methylimidazolium dicyanamide (Delta Hvap(298.15 K) = 174+-12 kJ mol-1) and N-butyl-N-methylpyrrolidinium dicyanamide (Delta Hvap(298.15 K) = 171+-12 kJ mol-1) are consistent with reported experimental values using electron impact ionization. The tunable vacuum ultraviolet source has enabled accurate measurement of photoion appearance energies. These appearance energies are in good agreement with MP2 calculations for dissociative photoionization of the ion pair. These experimental heats of vaporization, photoion appearance energies, and ab initio calculations corroborate vaporization of these RTILs as intact cation-anion ion pairs

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

Ab Initio Kinetics of Methylamine Radical Thermal Decomposition and H-Abstraction from Monomethylhydrazine by H-Atom

Methylamine radicals (CH3NH) and amino radicals (NH2) are major products in the early pyrolysis/ignition of monomethylhydrazine (CH3NHNH2). Ab initio kinetics of thermal decomposition of CH3NH radicals was analyzed by RRKM master equation simulations. It was found that β-scission of the methyl H-atom from CH3NH radicals is predominant and fast enough to induce subsequent H-abstraction reactions in CH3NHNH2 to trigger ignition. Consequently, the kinetics of H-abstraction reactions from CH3NHNH2 by H-atoms was further investigated. It was found that the energy barriers for abstraction of the central amine H-atom, two terminal amine H-atoms, and methyl H-atoms are 4.16, 2.95, 5.98, and 8.50 kcal mol–1, respectively. In units of cm3 molecule–1 s–1, the corresponding rate coefficients were found to be k8 = 9.63 × 10–20T2.596 exp(−154.2/T), k9 = 2.04 × 10–18T2.154 exp(104.1/T), k10 = 1.13 × 10–20T2.866 exp(−416.3/T), and k11 = 2.41 × 10–23T3.650 exp(−870.5/T), respectively, in the 290–2500 K temperature range. The results reveal that abstraction of the terminal amine H-atom to form trans-CH3NHNH radicals is the dominant channel among the different abstraction channels. At 298 K, the total theoretical H-abstraction rate coefficient, calculated with no adjustable parameters, is 8.16 × 10–13 cm3 molecule–1 s–1, which is in excellent agreement with Vaghjiani’s experimental observation of (7.60 ± 1.14) × 10–13 cm3 molecule–1 s–1 ( J. Phys. Chem. A 1997, 101, 4167−4171, DOI: 10.1021/jp964044z)

Method for predicting hypergolic mixture flammability limits: Application for non-ionic liquid based systems

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Temperature Jump Pyrolysis Studies Of Rp-2 Fuel

This paper explores the pyrolysis of RP-2, a rocket fuel derived from kerosene, on different catalytic surfaces relevant to endothermic cooling applications used in rockets. RP-2 fuel formulations contain thousands of compounds some of which breakdown at high temperatures by absorbing heat and sometimes form carbon deposits (coking). Thus the pyrolysis chemistry of RP-2 is an intense research topic. Here, Rapid Scan Fourier-TransformIinfrared (RS-FTIR) spectroscopy was used to measure the products of pyrolysis on different materials. The maximum temperature for the experiments was 800 °C with a temperature rise rate of 600 °C per second. Pressure in the chamber ranged from 5 to up to 25 atm. The materials chosen for the present experiments were nichrome and pure copper. The results show that pyrolysis products have a strong dependence on pressure

QSPR AND ARTIFICIAL NEURAL NETWORK PREDICTIONS OF HYPERGOLIC IGNITION DELAYS FOR ENERGETIC IONIC LIQUIDS

Due to their negligible volatility, energetic ionic liquids are being considered as next generation hypergolic fuels for replacing toxic monomethylhydrazine. One design challenge for energetic ionic liquids is to maintain their ignition delays as close to that of monomethylhydrazine. The ignition process of ionic liquids with an oxidizer, such as nitric acid, is a complex process and, to date, there are no theoretical methods for predicting the ignition delay. The present work examines two correlation methods, Quantitative Structure Property Relationship (QSPR) and Artificial Neural Networks (ANNs), for their ability to predict this quantity. A set of five descriptors were chosen from a pool of more than 160 to establish these correlations. A good QSPR correlation was obtained using these descriptors. We then trained an artificial neural network and examined the predictive ability of the network using an extensive 5-fold cross validation process with the same set of descriptors. A number of data normalization techniques were examined for network training and validation. The results show that ANNs exhibit excellent prediction capabilities for this application