Microparticle raman spectroscopy of multicomponent aerosols

Inelastic light scattering measurements (Raman and fluorescence spectroscopies) offer the possibility of chemically characterizing micrometer-size particles. Quantitative interpretation of such spectra is complicated by morphological or structural resonances associated with elastic and inelastic scattering. This paper explores the feasibility of using Raman spectroscopy to determine the composition of multicomponent microdroplets by examining the effects of such resonances and microdroplet size on the Raman signal. Raman scattering from electrodynamically suspended droplets of 1-octadecene and 1-bromohexadecane was found to be enhanced by morphology-dependent resonances. By applying Mie theory to the elastic scattering many of the increased Raman intensities were found to coincide with the incident beam resonances, but other peaks can be attributed to “output” resonances. It was also demonstrated that intensity fluctuations associated with resonances can be minimized by increasing the signal integration time, which permits changes in composition to be determined. In this way, the distillative evaporation of binary component droplets of 1,8-dibromooctane and hexadecane was followed by recording the Raman spectrum of the CBr bond. The effects of the system parameters on the interpretation of Raman spectra are elucidated.