Charles Q. Jiao

Ion chemistry in octafluorocyclobutane, c-C4F8

Abstract Cross-sections for electron impact ionization of octafluorocyclobutane (c-C4F8) have been measured from 10 to 200 eV by Fourier transform mass spectrometry. No parent ion is observed, and over half of the dissociative ionization yields C2F4+ and C3F5+. Eleven other fluorocarbon cations are produced with smaller cross-sections, giving a total ionization cross-section of (1.6±0.2)×10−15 cm2 between 80 and 200 eV. Only CF2+ and C2F3+ react further with the parent molecule to yield C3F5+ as the primary product. No evidence of cationic polymerization was found. F− and C4F8− are formed by electron attachment at energies below 10 eV, but neither reacts further with c-C4F8.

PARTIAL IONIZATION CROSS-SECTIONS OF C2F6

Abstract The dissociative ionization of perfluoroethane, C 2 F 6 , by electron impact has been measured under single-collision conditions using Fourier transform mass spectrometry. The total ionization cross-section rises to a maximum value of 8.9±1.3×10 −16 cm 2 at 70 eV. CF 3 + is the most prominent ion fragment at all energies, followed by C 2 F 5 + , CF + , and CF 2 + . C 2 F 6 + is not observed. The ratio of dissociative ionization to total dissociation increases from 27±5% at 22 eV to 89±11% at 70 eV. The total cross-section and the partitioning among the dissociative channels is examined in the context of the binary encounter Bethe (BEB) molecular orbital model.

Ionization of NF3 by electron impact

Abstract The ionization and dissociative ionization of NF 3 by electron impact has been measured by Fourier transform mass spectrometry (FTMS). The total ionization cross-section rises to a maximum value of 2.4±0.4×10 −16 cm 2 at 140 eV. Estimates of the total single ionization cross-section using ab initio energies with the binary encounter Bethe (BEB) [Y.K. Kim, M.E. Rudd, Phys. Rev. A 50 (1994) 3594] or Deutsch–Mark [Int. J. Mass Spec. 197 (2000) 37] models are roughly twice the measured values. The partial cross-sections creating NF x + ( x =0, 1, 2, 3), F + , and NF x 2+ ( x =1, 2, 3) are reported. Differences between the FTMS results and quadrupole data and fast atom beam results of Tarnovsky et al. [Int. J. Mass Spectrom. Ion Processes 133 (1994) 175] are discussed.

Ionization of 2,5-dimethylfuran by electron impact and resulting ion-parent molecule reactions

2,5-dimethylfuran (C6H8O) is an important fuel additive and a possible renewable liquid fuel for the future. This paper presents a recent Fourier transfer mass spectrometry study on the formation of ions from C6H8O by electron impact ionization and by ion-molecule reactions. Cross sections of the partial electron impact ionization have been measured and the pathways of major fragmentation channels of the parent ion have been examined. The kinetics of the reactions of C6H8O with selected product ions from electron impact and Ar+ have been studied.

Ionization of C3F8 by electron and ion impact

Abstract The dissociative ionization of perfluoropropane, C 3 F 8 , by electron impact has been measured under single collision conditions using Fourier Transform Mass Spectrometry. The total ionization cross-section rises to a maximum value of 1.24±0.20×10 −15 cm 2 at 140 eV. CF 3 + is the most prominent ion fragment at all energies, followed by C 3 F 7 + , CF + , CF 2 + , C 2 F 4 + and C 2 F 5 + ; C 3 F 8 + is not observed. The ratio of dissociative ionization to total dissociation increases from 25±8% at 22 eV to no less than 70% from 70 to 200 eV. Among the ion fragments only C 3 F 7 + reacts at room temperature to produce C 2 F 5 + .

Gas-phase ion chemistries in perfluoromethylcyclohexane

Electron impact ionization and ion–molecule reactions of perfluoromethylcyclohexane (C7F14) using Fourier-transfer mass spectrometry are reported. The electron impact ionization produces dominant ions and throughout most of the energy range of 10–200 eV, with the total ionization cross section peaking at ~100 eV with a value of 1.8 × 10−15 cm2. Numerous ions are observed at energies within a few electron volts of the lowest ionization threshold: , , , , , and . The lighter ions CF+, and are found to react with C7F14 forming and other product ions that we believe to result from further fragmentation of the intermediate ion . The charge transfer reaction between Ar+ and C4F14 yields similar product ions.

Mass spectrometry study of decomposition of exo-tetrahydrodicyclopentadiene by low-power, low-pressure rf plasma

The plasma cracking of exo-tetrahydrodicyclopentadiene (JP-10) (C10H16) is investigated using a quadrupole mass spectrometer. The relative densities of the JP-10 molecule and its principal decomposition products, including H2, are determined for varying rf powers in the range of 3–30 W, using the measured ion intensities combined with ionization cross section data from the literature. The extent of the cracking of JP-10 and the formation of H2 as functions of the rf power are discussed.

Cracking of selected hydrocarbon gases in a low-power, low-pressure RF plasma

The cracking of four hydrocarbons, C3H8, C2H6, C2H4 and CH4, separately, in an Ar plasma has been investigated. Ions observed in electron impact ionization mass spectra of the plasma are used to probe the neutral components of the plasma. A matrix of data of ion intensities under varying rf powers (0–30 W) and gas pressures (100–400 mTorr), for the four hydrocarbon gases has been collected, and the rates of the depletion of the hydrocarbons in the plasma and the formation of H2 from the cracking of the hydrocarbons, under the varying experimental conditions, have been evaluated. Among the four hydrocarbons, C2H4 undergoes cracking most readily and CH4 yields the most amount of H2 from plasma cracking.

Cracking of JP-10 In a Low-Power RF Plasma

The plasma cracking of JP-10 is investigated using a quadrupole mass spectrometer. The relative densities of the JP-10 molecule and its principal decomposition products including H2, are determined for varying rf powers in a range of 3-30 W, using the measured ion intensities combined with ionization cross section data from the literature. The extent of the cracking of JP10 and the formation of H2 as functions of the rf power are discussed.

Charge transfer reactions in Xe plasma expansion

Charge transfer reactions of fast Xe ions with hydrocarbons including methane (CH4), ethene (C2H4), and propane (C3H8) are studied by adding these hydrocarbon gases into a cross flowing Xe plasma expansion. Branching ratios and relative reaction rates for the charge transfers of fast Xe+ with each of the three hydrocarbon gases are measured under different rf powers of the inductively coupled Xe discharge. For CH4∕Xe system, we find that fast Xe+ reacts readily with CH4 generating CH4+ and CH3+ in a ratio of 1:0.56, with an estimated rate coefficient of (2.3±0.3)×10−10cm3∕s at 75W rf power which slowly increases to (2.9±0.3)×10−10cm3∕s at 250W (error bars reflect only the uncertainties due to the unknown extent of the ion recombination that follows the charge transfer reaction). These observed charge transfer reactions are made possible by the kinetically excited Xe ions produced by free expansion of the plasma. For the C2H4∕Xe system product ions C2H4+ and C2H2+ are observed, and for C3H8∕Xe, C2H4+ and C...