Toluene Cluster Formation in Laval Expansions: Nucleation and Growth.
J Phys Chem A
; 121(20): 3991-4001, 2017 May 25.
Article
em En
| MEDLINE
| ID: mdl-28481529
ABSTRACT
Toluene cluster formation has been investigated in the postnozzle flows of Laval expansions at flow temperatures between â¼48 and 73 K, toluene number concentrations between â¼1013 and 1015 cm-3, and for growth times of up to â¼170 µs. The clusters were detected by soft ionization mass spectrometry to ensure minimum cluster fragmentation upon ionization. The optimum conditions were achieved with single-photon ionization using vacuum ultraviolet (VUV) photons of 13.3 eV energy and low fluences. The nature of the onset of toluene cluster formation hints at barrierless nucleation, which seems a likely scenario for the high supersaturations (>1019) of the present experiments. This contrasts with the onset behavior observed for propane in earlier studies, which suggested nucleation in the presence of a barrier. Subsequent cluster growth has been studied as a function of the growth time for various toluene partial pressures. Size-resolved growth data have been recorded for all cluster sizes from the dimer to aggregates composed of â¼2400 monomers (â¼4.4 nm in size), revealing general trends in the growth behavior. The current experiments provide systematic size- and time-resolved data on cluster formation at high supersaturations as a possible benchmark for the understanding of cluster formation under such conditions.
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MEDLINE
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En
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2017
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Article