Accurate measurement of the optical constants for modeling organic and organophosphorous liquid layers and drops

We present accurate measurements for the optical constants for a series of organic liquids, including organophosphorous compounds. Bulk liquids are rarely encountered in the environment, but more commonly are present as droplets of liquids or thin layers on various substrates. Providing reference spectra to account for the plethora of morphological conditions that may be encountered under different scenarios is a challenge. An alternative approach is to provide the complex optical constants, n and k, which can be used to model the optical phenomena in media and at interfaces, minimizing the need for a vast number of laboratory measurements. In this work, we present improved protocols for measuring the optical constants for a series of liquids that span from 7800 to 400 cm-1. The broad spectral range means that one needs to account for both strong and weak spectral features that are encountered, all of which can be useful for detection, depending on the scenario. To span this dynamic range, both long and short cells are required for accurate measurements. These protocols are presented along with experimental and modeling results for thin layers of silicone oil on aluminum.

[1]  Tanya L. Myers,et al.  Quantitative total and diffuse reflectance laboratory measurements for remote, standoff, and point sensing , 2014, Defense + Security Symposium.

[2]  John E. Bertie,et al.  Infrared intensities of liquids. VIII: Accurate baseline correction of transmission spectra of liquids for computation of absolute intensities, and the 1036 cm-1 band of benzene as a potential intensity standard , 1991 .

[3]  Tanya L. Myers,et al.  Measurement of the infrared optical constants for spectral modeling: n and k values for (NH4)2SO4 via single-angle reflectance and ellipsometric methods , 2017, Defense + Security.

[4]  John E. Bertie,et al.  Liquid Water−Acetonitrile Mixtures at 25 °C: The Hydrogen-Bonded Structure Studied through Infrared Absolute Integrated Absorption Intensities , 1997 .

[5]  Eunja Kim,et al.  Time-Resolved Infrared Reflectance Studies of the Dehydration-Induced Transformation of Uranyl Nitrate Hexahydrate to the Trihydrate Form. , 2015, The journal of physical chemistry. A.

[6]  Tanya L. Myers,et al.  Measurement of infrared refractive indices of organic and organophosphorous compounds for optical modeling , 2017, Defense + Security.

[7]  John E. Bertie,et al.  Measurement and use of absolute infrared absorption intensities of neat liquids , 1995 .

[8]  B. Tatian,et al.  Fitting refractive-index data with the Sellmeier dispersion formula. , 1984, Applied optics.

[9]  Tanya L. Myers,et al.  Complex refractive index measurements for BaF 2 and CaF 2 via single-angle infrared reflectance spectroscopy , 2017 .

[10]  Tanya L. Myers,et al.  Infrared reflectance spectra: effects of particle size, provenance and preparation , 2014, Security and Defence.

[11]  Yin-Fong Su,et al.  Methods for quantitative infrared directional-hemispherical and diffuse reflectance measurements using an FTIR and a commercial integrating sphere. , 2018, Applied optics.

[12]  L. J. Bellamy The infra-red spectra of complex molecules , 1962 .

[13]  John E. Bertie,et al.  Infrared Intensities of Liquids XII: Accurate Optical Constants and Molar Absorption Coefficients between 6225 and 500 cm−1 of Benzene at 25°C, from Spectra Recorded in Several Laboratories , 1993 .

[14]  John E. Bertie,et al.  Infrared intensities of liquids XVI. Accurate determination of molecular band intensities from infrared refractive index and dielectric constant spectra , 1994 .

[15]  John E. Bertie,et al.  Infrared Intensities of Liquids XI: Infrared Refractive Indices from 8000 to 2 cm−1, Absolute Integrated Intensities, and Dipole Moment Derivatives of Methanol at 25°C , 1993 .

[16]  Yin-Fong Su,et al.  Quantitative reflectance spectra of solid powders as a function of particle size. , 2015, Applied optics.

[17]  Toya N. Beiswenger,et al.  Experimental effects on IR reflectance spectra: particle size and morphology , 2016, SPIE Defense + Security.

[18]  John E. Bertie,et al.  Infrared Intensities of Liquids XIII: Accurate Optical Constants and Molar Absorption Coefficients between 6500 and 435 cm−1 of Toluene at 25°C, from Spectra Recorded in Several Laboratories , 1994 .

[19]  M. Querry,et al.  Optical constants of minerals and other materials from the millimeter to the ultraviolet , 1987 .

[20]  Tanya L. Myers,et al.  The influence of particle size on infrared reflectance spectra , 2014, Defense + Security Symposium.

[21]  T. L. Myers,et al.  Accurate Measurement of the Optical Constants n and k for a Series of 57 Inorganic and Organic Liquids for Optical Modeling and Detection , 2017, Applied spectroscopy.