“Modifications for signal improvements within a custom-built Raman Spectrometer instrument for heterogeneous atmospheric reactions”

Beni Dangi; Kenley Herbert

Florida A&M University

For the past decade there has been major improvements in the observation and modeling of planetary atmospheres. Observations and models are often utilized to understand the composition of atmospheres. From the most abundant chemical species to the most favored reactions, there are vast amounts of information we can obtain from both useful tools. Although very useful, there are discrepancies between the observational and modeling data. In my laboratory we plan to do experiments to bridge the gap between such observation and modeling techniques. An instrument was designed, consisting of a custom-built reaction chamber combined with an acoustic levitator, a tunable monochromatic light source, and a custom-built Raman spectrometer system. The reaction chamber was vacuum-tested and coupled with an acoustic levitator that allows contactless sample handling. The calibration and performance of the Raman spectrometer was studied utilizing gated detection and three different gratings for a desired resolution and photon collection range. A wide range of 186−5000 cm−1 Raman shift, with a small uncertainty of ±2 cm−1, can be recorded covering a complete vibrational range in chemical reaction monitoring. The gating of the detector allowed operation under the room light and filtration of unwanted sample fluorescence. The in-situ reaction and monitoring of physical and chemical changes of samples by the Raman system were demonstrated by degradation of polystyrene spheres by monochromatic UV light. This instrument provides a versatile platform for in-situ investigation of surface reactions, under controlled pressure and radiation conditions, without external support structures. This instrument can be applied to various disciplines such as astrochemistry, and molecular biology. Modifications were made to our reaction chamber to allow adjustments of the acoustic levitator during experiments. Adjustments to the acoustic nodes are necessary for different vacuum/gas medium as well as different material based on various densities of materials.