Hydroxylammonium nitrate (HAN) is a promising candidate to replace highly toxic hydrazine in monopropellant thruster space applications. The reactivity of HAN aerosols on heated copper and iridium targets was investigated using tunable vacuum ultraviolet photoionization time-of-flight aerosol mass spectrometry. The reaction products were identified by their mass-to-charge ratios and their ionization energies. Products include NH 3 , H 2 O, NO, hydroxylamine (HA), HNO 3 , and a small amount of NO 2 at high temperature. No N 2 O was detected under these experimental conditions, despite the fact that N 2 O is one of the expected products according to the generally accepted thermal decomposition mechanism of HAN. Upon introduction of iridium catalyst, a significant enhancement of the NO/HA ratio was observed. This observation indicates that the formation of NO via decomposition of HA is an important pathway in the catalytic decomposition of HAN.

Because of the unusually high heats of vaporization of room-temperature ionic liquids (RTILs), volatilization of RTILs through thermal decomposition and vaporization of the decomposition products can be significant. Upon heating of cyano-functionalized anionic RTILs in vacuum, their gaseous products were detected experimentally via tunable vacuum ultraviolet photoionization mass spectrometry performed at the Chemical Dynamics Beamline 9.0.2 at the Advanced Light Source. Experimental evidence for di- and trialkylimidazolium cations and cyano-functionalized anionic RTILs confirms thermal decomposition occurs primarily through two pathways: deprotonation of the cation by the anion and dealkylation of the imidazolium cation by the anion. Secondary reactions include possible cyclization of the cation and C2 substitution on the imidazolium, and their proposed reaction mechanisms are introduced here. Additional evidence supporting these mechanisms was obtained using thermal gravimetric analysis-mass spectrometry, gas chromatography-mass spectrometry, and temperature-jump infrared spectroscopy. In order to predict the overall thermal stability in these ionic liquids, the ability to accurately calculate both the basicity of the anions and their nucleophilicity in the ionic liquid is critical. Both gas phase and condensed phase (generic ionic liquid (GIL) model) density functional theory calculations support the decomposition mechanisms, and the GIL model could provide a highly accurate means to determine thermal stabilities for ionic liquids in general.

The heats of vaporization of the room temperature ionic liquids (RTILs) N-butyl-Nmethylpyrrolidinium 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 ∆H vap (298.15 K) = 195±19 kJ mol -1 . The observed heats of vaporization of 1-butyl-3-methylimidazolium dicyanamide (∆H vap (298.15 K) = 174±12 kJ mol -1 ) and N-butyl-N-methylpyrrolidinium dicyanamide (∆H vap (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.

In order to better understand the volatilization process for ionic liquids, the vapor evolved from heating the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIM(+)Br(-)) was analyzed via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and thermogravimetric analysis mass spectrometry (TGA-MS). For this ionic liquid, the experimental results indicate that vaporization takes place via the evolution of alkyl bromides and alkylimidazoles, presumably through alkyl abstraction via an S(N)2 type mechanism, and that vaporization of intact ion pairs or the formation of carbenes is negligible. Activation enthalpies for the formation of the methyl and ethyl bromides were evaluated experimentally, ΔH(‡)(CH(3)Br) = 116.1 ± 6.6 kJ/mol and ΔH(‡)(CH(3)CH(2)Br) = 122.9 ± 7.2 kJ/mol, and the results are found to be in agreement with calculated values for the S(N)2 reactions. Comparisons of product photoionization efficiency (PIE) curves with literature data are in good agreement, and ab initio thermodynamics calculations are presented as further evidence for the proposed thermal decomposition mechanism. Estimates for the enthalpy of vaporization of EMIM(+)Br(-) and, by comparison, 1-butyl-3-methylimidazolium bromide (BMIM(+)Br(-)) from molecular dynamics calculations and their gas phase enthalpies of formation obtained by G4 calculations yield estimates for the ionic liquids' enthalpies of formation in the liquid phase: ΔH(vap)(298 K) (EMIM(+)Br(-)) = 168 ± 20 kJ/mol, ΔH(f, gas)(298 K) (EMIM(+)Br(-)) = 38.4 ± 10 kJ/mol, ΔH(f, liq)(298 K) (EMIM(+)Br(-)) = -130 ± 22 kJ/mol, ΔH(f, gas)(298 K) (BMIM(+)Br(-)) = -5.6 ± 10 kJ/mol, and ΔH(f, liq)(298 K) (BMIM(+)Br(-)) = -180 ± 20 kJ/mol.

Combined data of photoelectron spectra and photoionization efficiency curves in

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.Keywords: ionic liquid, aerosol, ion pair, gas phase, photoionization efficiency, synchrotron Intact cations are observed whether the origin of the ion pair vapor is a bulk sample or a thin film heated for the vaporization. However, highly reactive ionic liquids show dissociative ionization as well as decomposition, and it becomes difficult to identify the intact cation signal and to distinguish thermal decomposition from fragmentation of ion pairs upon ionization. This makes it nearly impossible to study reaction mechanisms and kinetics of hypergolic ionic liquids because of the difficulty of detecting small changes in their complicated mass spectra.Typically ions with high internal energies fragment extensively producing a mass spectrum that contains a wide variety of abundant fragment ions. 35 The internal energy content of the molecular ion (M + ) is from two sources: the thermal energy from evaporation and the energy imparted by the ionization process. Molecular ions (M + ) of labile molecules can only be detected if the internal energy of the molecular ion is kept very low, by obtaining mass spectra with low photon energies and low temperatures. Aerosol particle generation [36][37][38][39][40][41] has previously been demonstrated as a new way to introduce fragile biomolecules into the gas phase with nearly fragmentation-free mass spectra by minimizing their internal energy imparted into the molecular ion in gas phase. We apply this new method to hypergolic IL studies, to produce isolated ion pairs in the gas phase from IL aerosol particles followed by thermal vaporization, and monitor the ion pair vapor by soft ionization using tunable vacuum ultraviolet (VUV) photoionization mass spectrometry. This report focuses on comparing the degree of fragmentation depending on the isolated ion pair vapor source of a hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Experimental ApparatusIsolated ion pairs of ionic liquids are generated in the gas phase by thermal vaporization of IL aerosol particles and are monitored using soft ionization detection with tunable vacuum ultraviolet (VUV) photoionization mass spectrometry. Those ion pairs that are generated by aerosol particles are compared to those generated by a conventional effusive beam. 26,28,29 The aerosol experimental apparatus at the Chemical Dynamics Beamline 9.0.2.1 of the Advanced Light Source in Berkeley, California, previously described in detail, 35 includes a particle generation system, a particle size analyzer, and an aerosol mass spectrometer (AMS). In the other sets of experiments, i...

We present the first direct measurement of a neutral, intact ion pair photoionization efficiency (PIE) curve for a vaporized ionic liquid, 1-butyl-3-methylimidazolium tricyanomethanide, using tunable vacuum ultraviolet (VUV) photoionization time-of-flight mass spectrometry (PI-TOFMS). The ionization potential (IP) for the ion pair is experimentally determined to be 6.6 ± 0.5 eV, which matches reasonably well with the adiabatic IP of 7.3 ± 0.2 eV calculated at the M06/6-31+G(d,p) level of theory. The lifetime to dissociation of the cation–radical complex formed upon ionization of the ion pair is highly dependent upon entropic contributions. Thermal gravimetric analyses (TGA) determined the enthalpy of vaporization to be ΔH vap(298 K) = 143.5 ± 6.2 kJ/mol and that vaporization of BMIM+TCM– as ion pairs is the dominant mechanism for mass loss under the experimental conditions for VUV PI-TOFMS (T = 433 K).

Broadband supercontinuum (SC) pulses in the few cycle regime are a promising source for spectroscopic and imaging applications. However, SC sources are plagued by poor stability, greatly limiting their utility in phase-resolved nonlinear experiments such as 2D photon echo spectroscopy (2D PES). Here, we generated SC by two-stage filamentation in argon and air starting from 100 fs input pulses, which are sufficiently high-power and stable to record time-resolved 2D PE spectra in a single laser shot. We obtain a total power of 400 μJ/pulse in the visible spectral range of 500-850 nm and, after compression, yield pulses with duration of 6 fs according to transient-grating frequency-resolved optical gating (TG-FROG) measurements. We demonstrate the method on the laser dye, Cresyl Violet, and observe coherent oscillations indicative of nuclear wavepacket dynamics.