Design and Performance of an Acoustic Levitator System Coupled with a Tunable Monochromatic Light Source and a Raman Spectrometer for In Situ Reaction Monitoring.

Abstract

The design and performance of a custom-built reaction chamber combined with an acoustic levitator, a tunable monochromatic light source, and a Raman spectrometer are reported. The pressure-compatible reaction chamber was vacuum-tested and coupled with the acoustic levitator that allows contactless sample handling, free of contingent sample requirements such as charge and refractive index. The calibration and performance of the Raman spectrometer was studied utilizing gated detection and three different gratings that can be interchanged within seconds 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 perturbation and monitoring of physical and chemical changes of samples by the Raman system were demonstrated by degradation of polystyrene by monochromatic UV light and photobleaching of a potato slice by visible light. This instrument provides a versatile platform for in situ investigation of surface reactions, without external support structures and under controlled pressure and radiation conditions, relevant to various disciplines such as materials science, astrochemistry, and molecular biology.