Micro Raman spectroscopy and Raman imaging for the study of (photo)reactivity and heterogeneity of single levitated droplets
Résumé
In atmospheric chemistry, each aerosol particle acts as a small mobile reactor where several heterogeneous chemical reactions lead to the modification of its size, chemical composition and structure; as well as the consumption and release of chemical agents from its gaseous environment. Despite its relevance, information on the chemical and photochemical processes that occur in atmospheric aerosols is still scarce, mainly due to the instrumental difficulties involved in studying such processes on a surface scale. In this regard, Micro-Raman spectroscopy coupled to a levitation technique, through an environmental levitation cell, is especially useful for studying - at micrometric scale - the in-situ modifications of aerosol when exposed to reactive or damp environments without the influence of a contacting surface (Krieger, et al. 2012).
This work deals with two main objectives. On one hand, the monitoring of physical- and photo-chemical processes occurring in levitated single particles; and in the other hand, the coupling and instrumental developments carried out to perform Raman imaging studies of single levitated particles. We will show the coupling between the confocal Raman microscope and the adapted photochemical environmental levitation cell, as well as the heterogeneous distribution of (photo)chemical products on levitated particles (less than 10 µm of size) evidenced by reconstruction of the Raman spectral image.
This work was supported by funds from the “Laboratoire d’Excellence” (LABEX) -CaPPA- (ANR-11-LABX-0005-01) and CPER research project CLIMIBIO.
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Krieger, U. K., Marcolli, C., and Reid, J. P. (2012). Chem. Soc. Rev. 41, 6631-6662.