Fourier transform infrared spectroscopy of a single aerosol particle

Gideon Sageev Grader, Stephen Arnold, Richard C. Flagan, John H. Seinfeld

Research output: Contribution to journalArticlepeer-review


A method is developed for obtaining the molecular composition of a single suspended microparticle by Fourier transform infrared spectroscopy. The particle is held in an electrodynamic balance and irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The laser is tuned to an edge of an optical resonance of the particle while the IR beam is chopped. Through evaporation and condensation the chopped IR beam causes a size modulation of the droplet, which in turn induces a fluctuation in the laser light scattered from the particle. The scattered light is detected at 90° with a photomultiplier, and the amplitude of the light fluctuation is measured with a lock-in amplifier. The lock-in signal is then inverted by a discrete fast Fourier transform routine (FFT), to yield the particle absorption spectrum. Spectra of (NH4)2SO 4 droplets at different solute concentrations are presented. The data shown include the first infrared spectrum of a highly supersaturated solution.

Original languageEnglish (US)
Pages (from-to)5897-5903
Number of pages7
JournalThe Journal of Chemical Physics
Issue number11
StatePublished - 1987

ASJC Scopus subject areas

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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