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A velocity map imaging photoelectron spectrometer for the study of ultrafine aerosols with a table-top VUV laser and Na-doping for particle sizing applied to dimethyl ether condensation
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10.1063/1.4788620
/content/aip/journal/jcp/138/4/10.1063/1.4788620
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/4/10.1063/1.4788620

Figures

Image of FIG. 1.
FIG. 1.

Drawing of the experimental setup consisting of the source chamber (A), the Na-oven chamber (B), the ionization/detection chamber (C), and the four-wave mixing chamber (D), and the diffraction grating chamber (E). See text for details.

Image of FIG. 2.
FIG. 2.

(a) Xenon photoelectron image obtained upon ionization with photons of 13.318 eV energy. (Left) Raw image. (Right) Reconstructed image. The sharp ring arises from photoelectrons from ionization to the 2P3/2 spin orbit state of the ion. The double-headed arrow (pol.) denotes the linear polarization of the VUV light. The direction of the cluster/particle beam is perpendicular to the detector plane. (b) Electron kinetic energy (KE) distribution in the region of the 2P3/2 spin orbit state corresponding to the speed distribution of the reconstructed photoelectron image in (a).

Image of FIG. 3.
FIG. 3.

(a) Size distribution of DME clusters determined from a mass spectrum of Na-doped DME clusters recorded after ionization with UV light of 4.66 eV energy (Na-doping method). (b) Size distribution of the same original cluster distribution as in trace (a), but recorded after ionization with 13.318 eV VUV light instead of UV light. The mass peaks after VUV ionization in trace (b) correspond to protonated cluster masses, which are formed by the fast intermolecular proton transfer given in Eq. (3) . Note that this reaction does not take place upon UV ionization of the Na-doped clusters (trace a). N: number of monomer units per cluster. Ø: cluster diameter.

Image of FIG. 4.
FIG. 4.

Size distributions of DME clusters and ultrafine aerosol particles determined in this work for the investigation of size-dependent effects in photoelectron spectra (Sec. III B ). Data were recorded with the Na-doping method. Conditions I-VI: see Table I . Note that individual cluster/particles ion signals are only resolved up to about N = 100. N: number of monomer units per cluster/particle. Ø: cluster/particle diameter.

Image of FIG. 5.
FIG. 5.

Photoelectron image of (a) DME monomer (condition I) (b) ultrafine DME aerosol (condition V) obtained upon ionization with VUV light at 13.318 eV. The double-headed arrow denotes the linear polarization of the VUV light. Conditions I and V: see Table I . Note that the absolute color scales are different in panels (a) and (b).

Image of FIG. 6.
FIG. 6.

Experimental size-dependent photoelectron spectra of DME monomer/clusters/particles for beam conditions I-VI (see Table I ) as a function of the electron binding energy (BE). Ionization was performed with light at 13.318 eV. The lines under the spectra correspond to fits of the experimental spectra using Gaussian functions. The asterisks label the positions (maxima) of the energetically lowest band (transition from 2b1). The maximum of the monomer 2b1 band is marked with a dashed line.

Image of FIG. 7.
FIG. 7.

Fitted photoelectron spectra from Fig. 6 , but with the monomer contributions subtracted for conditions II-VI. The asterisks label the positions (maxima) of the energetically lowest band (transition from 2b1).

Image of FIG. 8.
FIG. 8.

Time-of-flight mass spectrum in the region of the DME monomer fragment ion CH3OCH2 + (m/z = 45), the DME monomer parent ion CH3OCH3 + (m/z = 46), and the protonated DME ion CH3OHCH3 + (m/z = 47) recorded under (a) monomer condition (condition I), and (b) cluster condition II. Note that the protonated ion cannot appear under condition I. Ionization was performed with light at 13.318 eV. Conditions I and II: see Table I .

Image of FIG. 9.
FIG. 9.

Kinetic energy (KE) distributions of (a) the dehydrogenated DME ion m/z = 45, and (b) the DME parent ion m/z = 46. Upper traces: recorded under monomer condition (condition I). Lower traces: recorded under particle condition V. Ionization was performed with light at 13.318 eV. Conditions I and V: see Table I .

Image of FIG. 10.
FIG. 10.

Kinetic energy (KE) distribution of the protonated DME ion m/z = 47 recorded under particle condition II (see Table I ). Ionization was performed with light at 13.318 eV.

Tables

Generic image for table
Table I.

Experimental conditions for the formation of DME momomer/cluster/particle beams used in this work. The Roman numerals used in this table are used throughout the text and all figures to refer to the respective cluster/particle distributions. p vapor is the DME partial pressure in the sample gas mixture. T nozzle is the nozzle temperature. See text for the explanation of the “delay.”

Generic image for table
Table II.

Geometric mean diameter (dg), geometric standard deviation (σg), mass mean diameter (dm), and maximum diameter (dmax) from lognormal fits to the size distributions of DME clusters/particles shown in Fig. 4 . Conditions: see Table I .

Generic image for table
Table III.

First ionization energies (IE; values at band maxima) and full widths at half maximum (FWHM) of the energetically lowest lying band (ionization from 2b1) shown in the photoelectron spectra in Fig. 6 . (Uncertainties of the IE represent experimental uncertainties. Uncertainties of the FWHM represent 3 standard deviations due to statistical errors). Conditions: see Table I .

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/content/aip/journal/jcp/138/4/10.1063/1.4788620
2013-01-30
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: A velocity map imaging photoelectron spectrometer for the study of ultrafine aerosols with a table-top VUV laser and Na-doping for particle sizing applied to dimethyl ether condensation
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/4/10.1063/1.4788620
10.1063/1.4788620
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