A new broadly tunable (7.4-10.2 eV) laser based VUV light source and its first application to aerosol mass spectrometry

S. J. Hanna, P. Campuzano-Jost*, E. A. Simpson, D. B. Robb, I. Burak, M. W. Blades, J. W. Hepburn, A. K. Bertram

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

64 Scopus citations

Abstract

A laser based vacuum ultraviolet (VUV) light source using resonance enhanced four wave difference mixing in xenon gas was developed for near threshold ionization of organics in atmospheric aerosol particles. The source delivers high intensity pulses of VUV light (in the range of 1010 to 1013 photons/pulse depending on wavelength, 5 ns FWHM) with a continuously tunable wavelength from 122 nm (10.2 eV) to 168 nm (7.4 eV). The setup allows for tight (<1 mm2) and precise focusing (μrad pointing angle adjustability), attributes required for single particle detection. The generated VUV is separated from the pump wavelengths by a custom monochromator which ensures high spectral purity and minimizes absorptive losses. The performance of the source was characterized using organic molecules in the gas phase and optimal working conditions are reported. In the gas phase measurements, photoionization efficiency (PIE) curves were collected for seven different organic species with ionization energies spanning the full wavelength range of the VUV source. The measured appearance energies are very close to the literature values of the ionization energies for all seven species. The effectiveness of the source for single particle studies was demonstrated by analysis of individual caffeine aerosols vaporized by a pulsed CO2 laser in an ion trap mass spectrometer. Mass spectra from single particles down to 300 nm in diameter were collected. Excellent signal to noise characteristics for these small particles give a caffeine detection limit of 8 × 105 molecules which is equivalent to a single 75 nm aerosol, or approximately 1.5% of a 300 nm particle. The appearance energy of caffeine originating from the aerosol was also measured and found to be 7.91 ± 0.05 eV, in good agreement with literature values.

Original languageEnglish
Pages (from-to)134-146
Number of pages13
JournalInternational Journal of Mass Spectrometry
Volume279
Issue number2-3
DOIs
StatePublished - 15 Jan 2009

Funding

FundersFunder number
NRC-NSERC-BDC
Natural Sciences and Engineering Research Council of Canada
Canada Foundation for Innovation
Canadian Foundation for Climate and Atmospheric Sciences
British Columbia Knowledge Development Fund

    Keywords

    • Aerosol mass spectrometry
    • Photoionization efficiency
    • Vacuum ultraviolet light

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