Dust Library of Plasmonically Enhanced Infrared Spectra of Individual Respirable Particles

Abstract

This work characterizes collections of infrared spectra of individual dust particles of ∼4 µm size that were obtained from three very different environments: our lab air, a home air filter, and the 11 September 2001 World Trade Center event. Particle collection was done either directly from the air or by placing dust powder from various samples directly on the plasmonic mesh with 5 µm square holes as air is pumped through the mesh. This arrangement enables the recording of "scatter-free" infrared absorption spectra of individual particles of size comparable to the probing wavelengths whose vibrational signatures are otherwise dominated by scattering and dispersive line shape distortions. The spectra are sensitive to the amounts of various infrared active components and analysis using a Mie-Bruggeman model for mixed composition particles provides volume fractions of the components. Inhalation of dust particles of ∼4 µm size has significant health consequences as these are among the largest inhaled into people's lungs. The chemical composition of ∼4 µm respirable particles is of great interest from health, atmospheric, and environmental perspectives as different environments may pose different hazards and spectroscopic challenges.

Etalon-Assisted Determination of the Complex Index of Refraction of a Solution for the Study of Strong Cavity–Vibrational Coupling of PF6– in Acetonitrile

“…A Lorentz oscillator or damped harmonic oscillator model − was employed because it gives the dielectric function [electrical permittivity, ϵ (ν̃)] as a linear sum of vibrational terms. The square root of ϵ (ν̃) is the complex index of refraction N (ν̃) that is needed for TM simulations, as well as being a compendium of the absolute intensities of the vibrations bold-italicN ( ν̃ ) = n ( ν̃ ) + normali k ( ν̃ ) = bold-italicϵ ( ν̃ ) = ε 0 + prefix∑ j A j ν̃ 0 , j 2 ν̃ 0 , j 2 − ν̃ 2 − normali normalΓ j ν̃ where ε 0 is the permittivity value at the highest wavenumber, j is an index over the vibrations, ν̃ 0, j is the peak position, A j is the peak intensity, and Γ j is the peak full width at half-maximum.…”

Etalon-Assisted Study of the Strong CO Ligand Vibrations of the fac-[Re(CO)3(bpy)(CH3CN)]+ Octahedral Complex

“…Finally, the data in Figure a and Table are both used to constrain a Lorentz oscillator − model of the dielectric function, which is connected to the absolute intensities of the vibrations where is the electrical permittivity, ε 0 is the permittivity value at the highest wavenumber, j is an index over the vibrations, is the peak position, A j is the peak intensity, and Γ j is the peak full width at half-maximum. The and Γ j were fixed by fitting from the corrected ATR-IR spectrum, so the final task is to find the intensity values of A j (of eq ) that optimally fit both the solution’s real indices of refraction (Table ) from etalon fringes and the scaled and corrected ATR-IR spectrum converted to (see Figure a).…”

“…Finally, the data in Figure a and Table are both used to constrain a Lorentz oscillator − model of the dielectric function, which is connected to the absolute intensities of the vibrations bold-italicN ( ν̃ ) = n ( ν̃ ) + i k ( ν̃ ) = bold-italicϵ ( ν̃ ) = ε 0 + ∑ j A j ν̃ 0 , j 2 ν̃ 0 , j 2 − ν̃ 2 − i Γ j ν̃ where bold-italicϵ ( ν̃ ) is the electrical permittivity, ε 0 is the permittivity value at the highest wavenumber, j is an index over the vibrations, ν̃ 0 , j is the peak position, A j is the peak intensity, and Γ j is the peak full width at half-maximum. The ν̃ 0 , j and Γ j were fixed by fitting k …”

Changing Vibration Coupling Strengths of Liquid Acetonitrile with an Angle-Tuned Etalon

“…The best literature complex index of refraction, N , of acetontrile has a digital form, and it has been fit to an analytical form as the square root of a sum of Lorentz oscillators (damped harmonic oscillators): where ε 0 is a high wavenumber value fixed at 1.3340 2 = 1.7796 for acetonitrile, A j is a unitless measure of transition strength of vibration j , ν̃ 0, j is the vibrational peak position in wavenumbers, and Γ j is the full width at half-maximum of the vibration in wavenumbers. With the complex index of refraction expressed in terms of vibrations, it becomes possible to predict the transmission spectrum without the effect of target vibrations.…”