Novel high-temperature and pressure-compatible ultrasonic levitator apparatus coupled to Raman and Fourier transform infrared spectrometers

Abstract

We describe an original apparatus comprising of an acoustic levitator enclosed within a pressure-compatible process chamber. To characterize any chemical and physical modifications of the levitated particle, the chamber is interfaced to complimentary, high-sensitivity Raman (4390-170 cm(-1)), and Fourier transform infrared (FTIR) (10,000-500 cm(-1)) spectroscopic probes. The temperature of the levitated particle can be accurately controlled by heating using a carbon dioxide laser emitting at 10.6 μm. The advantages of levitating a small particle combined with the two spectroscopic probes, process chamber, and infrared laser heating makes novel experiments possible relevant to the fields of, for example, planetary science, astrobiology, and combustion chemistry. We demonstrate that this apparatus is well suited to study the dehydration of a variety of particles including minerals and biological samples; and offers the possibility of investigating combustion processes involving micrometer-sized particles such as graphite. Furthermore, we show that the FTIR spectrometer enables the study of chemical reactions on the surfaces of porous samples and scientifically and technologically relevant, micrometer-thick levitated sheets. The FTIR spectrometer can also be used to investigate non-resonant and resonant scattering from small, irregularly-shaped particles across the mid-infrared range from 2.5 μm to 25 μm, which is relevant to scattering from interplanetary dust and biological, micrometer-sized samples but cannot be accurately modelled using Mie theory.

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

“…The overall Raman system design is similar to that reported by Bennett et al 25 and Brotton and Kaiser. 4 In addition to photon collection optics, the major difference in our system from the above-mentioned systems lies in three available gratings that can be interchanged within seconds to achieve desired spectral resolution and range as well as smaller camera pixel size of 13 μm compared to 26 μm.…”

“…In such laboratory experiments, gas–surface, heterogeneous reactions are of particular interest to investigate cloud and haze dynamics. 5 , 15 In a gas–surface reaction investigation, reactions of unsaturated hydrocarbon gases on the surface of silicon single particle had been performed, 4 where selected hydrocarbon gases are adsorbed on the surface and polymerized to refractory carbonaceous compounds whose spectroscopic signatures matched with the meteoritic sample providing insights into the possible formation conditions of the carbonaceous compounds in the meteoritic sample. A model mechanistic computational study 16 showed that 1,3-butadiene (H 2 CHCHCH 2 ) can adsorb exothermically on the silicon surface propagated by a second H 2 CHCHCH 2 molecule adsorption with further release of energy.…”

Beyond the Langevin horn: Transducer arrays for the acoustic levitation of liquid drops

“…The current state of the art for spectroscopic analysis of levitated liquid droplets using a conventional piezoelectric horn levitator is reported by Brotton et al [21,23]. In this work a piezoelectric transducer oscillates at 58 kHz (using v=fλ and the speed of sound in air at STP, yields a wavelength in air of about 5.9mm).…”

Toward the Formation of Carbonaceous Refractory Matter in High Temperature Hydrocarbon-Rich Atmospheres of Exoplanets Upon Micrometeoroid Impact

“…To monitor the chemical modifications of the levitated particles, Raman spectra were recorded on line and in situ (Brotton & Kaiser 2013a, 2013b. A Q-switched Nd:YAG laser (Crystalaser: QG-532-1W) was operated at 532 nm, repetition rate of 500 Hz, output power of 200 mW, and pulse width of 13.5 ns.…”