Tunable Wavelength Soft Photoionization of Ionic Liquid Vapors

Strasser, Daniel; Goulay, Fabien; Belau, Leonid; Kostko, Oleg; Koh, Christine J.; Chambreau, Steven D.; Vaghjiani, Ghanshyam L.; Ahmed, Musahid; Leone, Stephen R.

doi:10.1021/jp909727f

Cited by 29 publications

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References 33 publications

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“…Mass spectra obtained The intact cation, Bmim + (139 amu), that is observed in the mass spectra of the aerosol source beam is most likely produced by dissociative photoionization (eq 1). This is typical evidence 24,26,29 for the production of an isolated ion pair in the gas phase upon vaporization of . Furthermore no parent ionic liquid mass is observed, similar to previous studies.…”

Section: Resultsmentioning

confidence: 81%

“…Recent studies [21][22][23][24][25][26][27][28][29][30][31][32][33] show that isolated ion-pairs can be prepared in the gas phase by thermal vaporization of ILs despite their extremely low vapor pressure. Earle and collaborators 34 reported in 2006 that intact cations (C + ) and anions (A -) associated in the vapor are produced by vaporization, and this result initiated multiple studies that investigate the vaporization mechanism and the nature of IL vapor.…”

Section: Introductionmentioning

confidence: 99%

“…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, isolated ion pairs are prepared as an effusive beam, which is a typical pyrolysis source using an aluminum oven body with a glass interior heated by resistive heater cartridges.…”

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Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

et al. 2011

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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...

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Section: Resultsmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

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“…Details of the experiment and the effusive source have been described previously. 35,36 Briefly, photoionization mass spectra were measured from 8.0 to 15.0 eV in 0.1 eV steps at 457 K. At each energy, the spectrum was averaged over 500 000 pulses of the ion repeller.…”

Section: ' Introductionmentioning

confidence: 99%

Thermal Decomposition Mechanism of 1-Ethyl-3-methylimidazolium Bromide Ionic Liquid

et al. 2011

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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.

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“…In the limited photon energy range investigated here (8.5−14.5 eV), we do not detect H 2 or N 2 , as their IE values are 15.4 and 15.6 eV, 23 respectively. Experimental photoionization energies are determined by fitting the photoionization efficiency curves (PIE) at the photoion onset as described previously 24 (see Figure 2). …”

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

et al. 2016

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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.

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Tunable Wavelength Soft Photoionization of Ionic Liquid Vapors

Abstract: Combined data of photoelectron spectra and photoionization efficiency curves in

Cited by 29 publications

References 33 publications

Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

Thermal Decomposition Mechanism of 1-Ethyl-3-methylimidazolium Bromide Ionic Liquid

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

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