Photoionization mass spectrometry of combustion radicals. Final technical report Page: 9 of 26
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photoelectrons produced by the VUV
beam[11-141 was quite helpful for the
detection of major flame species (CH4,
H20, HCI, CO, CO2, 02, Ar) with
ionization potentials above the 8.2-10.0
eV energies of the tunable VUV laser.
Ion masses of several of these species
are indicated in the mass spectrum
displayed in Fig. 5. Also shown in Fig. 5
are radical intermediates (C2H3, HCO,
C3H, C3H) directly ionized by the VUV,
typically present in concentrations 10'3
to 10~ below those of the major species.
Fig. 6 displays mass peaks for
dichloroketene and dichloroethenol
produced with a photon energy of 10.5
eV (obtained by tripling the Nd-YAG third
harmonic in a xenon cell), well above
their respective ionization thresholds of
Ion Mass (amu)
Figure 6: Partial TOFMS ion spectrum for
dichloroketene and dichloroethenol.
9.15 and 9.08 eV. The 35C137CI dichloroketene isotopomer of m/z =112 overlaps the
35CI35CI isotopomer of dichloroethenol at this photon energy. By reducing the
ionization energy to 9.12 eV, just below the threshold for ionization of dichloroketene,
all three (35CI35CI, 35CI37CI, 37C137CI)
isotopomers of dichloroethenol appear
separately with relative signals 0.007., ...,.,.,
corresponding to their respective -1 ~m, 9.1 .V
isotopic abundances, as shown in Fig. 7. 0.006 -Dstan"e - 2.5 mm
Figs. 6 and 7 illustrate the importance of
the proper choice of VUV wavelength r 0.005
for monitoring the concentration of a .e 0.004
given species. Indeed, as is discussed in v
Section Ill-B, measurement of the PIE 50.003
curve often provides an unambiguous .0
identification of one of several possible 0.002
structural isomers. -
A. Relative Concentration Profiles 0.000 - -
A series of time-of-flight mass spectra,
taken for each of several positions of the
sampling cone relative to the burner
face, and recorded for a number of
different photon energies spanning the
105 110 112 114 115
Ion Mass (amu)
Figure 7: TOFMS ion spectrum for
-istance - 2.75 5ev
C! / -o H\ -
p * * p . .-
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Cool, T.A. Photoionization mass spectrometry of combustion radicals. Final technical report, report, December 31, 1998; United States. (digital.library.unt.edu/ark:/67531/metadc684924/m1/9/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.