Related Experiment Video
Updated: Oct 25, 2026

Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems
Published on: June 23, 2023
Infrared Complex Refractive Indices of Seven Polycyclic Aromatic Hydrocarbons
Jessica M O Salcido1,2, Jeremy D Erickson1, Ashley M Bradley1
1Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington99354, United States.
Abstract:
Polycyclic aromatic hydrocarbons (PAHs) are environmentally and astrophysically significant toxic organic compounds, several of which are carcinogenic. Infrared spectroscopy provides a nondestructive, standoff method of detecting and monitoring PAHs. Analysis of any infrared measurements, however, is complicated by the fact that measured extinction depends not only on molecular absorption features but also on electromagnetic scattering due to particle size and morphology. Quantitative interpretation therefore requires knowledge of the morphologically independent optical properties of the material, specifically the complex refractive indices n(ν̃) and k(ν̃). This work reports n(ν̃) and k(ν̃) of seven condensed-phase PAHs: naphthalene, phenanthrene, pyrene, benzo[a]pyrene, benzo[e]pyrene, benzo[ghi]perylene, and coronene. Wavelength-dependent complex refractive indices were derived in the mid-infrared (7800-400 cm-1) at room temperature (296 K) using quantitative, gravimetric potassium bromide (KBr) pellet transmission spectroscopy. The precision of the method was evaluated through a variability study of 15 KBr pellets of pyrene. The resulting complex refractive indices are then applied to model pyrene aerosol absorption spectra, demonstrating their utility for future morphology-dependent identification and quantitative interpretation of PAHs in infrared observations.
Related Concept Videos
NMR Spectroscopy of Aromatic Compounds
IR Absorption Frequency: Hybridization
Among the sp, sp2, and sp3 hybridized orbitals, sp orbitals have the maximum s character (50%). Consequently, the electrons are held more closely to the nucleus, resulting in stronger and shorter C–H bonds that stretch at a...
Five-Membered Heterocyclic Aromatic Compounds: Overview
Infrared (IR) Spectroscopy: Overview
Different compounds display unique properties due to their...
IR Spectrum
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0% (complete...
IR Frequency Region: X–H Stretching

