Articles you may be interested inA new, low temperature long-pass cell for mid-infrared to terahertz spectroscopy and synchrotron radiation use Rev. Sci. Instrum. 84, 093101 (2013); 10.1063/1.4819066Mie scattering enhanced near-infrared light response of thin-film silicon solar cells Appl. Phys. Lett. 97, 063507 (2010);A method is described for forming and spectroscopically characterizing cryogenic aerosols formed in a low temperature gas cell. By adjusting the cell pressure, gas composition and flow rate, the size distribution of aerosol particles can be varied over a wide range. The combination of pressure and flow rate determine the residence time of the aerosols in the cell and hence the time available for the particles to grow. FfIR spectroscopy, over the range from 600 to 6000 em -I , is used to characterize the aerosols. The particle size distribution can be varied so that, at one extreme, the spectra show only absorption features associated with the infrared active vibrational bands and, at the other, they display both absorption and Mie scattering. In the latter case, Mie scattering theory is used to obtain semiquantitative aerosol size distributions, which can be understood in terms of the interplay between nucleation and condensation. In the case of acetylene aerosols, the infrared spectra suggest that the particles exist in the high temperature cubic phase of the solid.
Fourier Transform Infrared Spectroscopy has been used to study homogeneously nucleated hydrazine (N2H4) aerosols formed in a variable temperature flow cell. The spectra contain both resonant absorptions and Mie scattering features which allow detailed information to be obtained on the phase of the aerosol particles and the size distribution that is formed. In addition, the relative intensities of the absorption and scattering features can be used as a qualitative probe of the density of the particles. A disordered phase is observed at cell temperatures ranging from 230 to 180 K and a transition to a crystalline phase occurs over the temperature range 180–175 K. At lower temperatures the infrared spectra become progressively narrower, indicating that the quality of the crystals improves as the temperature is lowered. The result is previously unobserved details in the hydrazine N‐H stretch vibrations of the crystalline solid. The high quality of the spectra obtained under these conditions suggests that at the high condensation rates characteristic of the present experiments, self‐annealing yields highly crystalline particles. Mie calculations, based upon the complex refractive index data for amorphous solid hydrazine, are shown to have utility in modeling the infrared spectrum of the disordered phase, which we tentatively assign as a supercooled liquid.
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