Large molecules, radicals, ions, and small soot particles in fuel-rich hydrocarbon flames - Part III: REMPI mass spectrometry of large flame PAHs andfullerenes and their quantitative calibration through sublimation

Citation
J. Ahrens et al., Large molecules, radicals, ions, and small soot particles in fuel-rich hydrocarbon flames - Part III: REMPI mass spectrometry of large flame PAHs andfullerenes and their quantitative calibration through sublimation, BER BUN GES, 102(12), 1998, pp. 1823-1839
Citations number
57
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
BERICHTE DER BUNSEN-GESELLSCHAFT-PHYSICAL CHEMISTRY CHEMICAL PHYSICS
ISSN journal
0940-483X → ACNP
Volume
102
Issue
12
Year of publication
1998
Pages
1823 - 1839
Database
ISI
SICI code
0005-9021(199812)102:12<1823:LMRIAS>2.0.ZU;2-Z
Abstract
Large polycyclic aromatic hydrocarbons (PAHs) and fullerenes have been stud ied using nozzle/molecular beam sampling from flames and from a sublimator with subsequent resonance enhanced multi-photon ionization (REMPI) mass spe ctrometry. The mass spectrometer was of the time-of-flight type with an ion reflector. The sublimator for large molecules generated a definite gas pha se concentration of the respective PAHs or fullerene which was controlled b y determining the mass loss of the substance in a stream of heated nitrogen . The purpose of these calibrations is the quantitative analysis of these l arge molecules when sampling fuel-rich flames. Twenty-three PAHs with masse s up to 596 u (dicoronylene), some oxygen-containing PAHs, C-60, C-70 and C -84 were used. Sublimation energies of low-volatility PAHs and of fullerene s were determined. Multi-photon ionization of PAHs and fullerenes was investigated as function of the effective laser power density in the ion source and the wavelength. Furthermore, ion fragmentation of large PAHs and fullerenes was studied fo r different power densities and wavelengths. For PAHs with up to about 20 C atoms a wave length of 265 nm with laser power densities of 0.5 to 1 MW/cm (2) are suitable. For larger PAHs, C-60,C- and C-70 a wavelength of 208 nm is more favorable. At the shorter wavelength PAHs have considerably higher ionization efficiencies and the fullerenes do not show delayed ionization a nd fragmentation. Quantitative relationships between the ion signal and the absolute number density for a large number of PAHs and fullerenes in the s ource were determined for standardized inflow and ionization conditions.