Infrared Spectra and Intensities of Amorphous and Crystalline Allene

Abstract

The infrared (IR) spectra, including spectral intensities, of solid hydrocarbons are of interest to astrochemists and astronomers for the relevance of these compounds to surface chemistry in the outer solar system and beyond. However, although the vibrational modes and IR peak positions of many such compounds have long been studied, much less attention has been paid to the IR intensities needed to quantify both astronomical observations and laboratory results. Here we present mid- and near-IR transmission spectra of a relatively little-studied solid hydrocarbon, allene (1,2-propadiene). Spectra of both amorphous and polycrystalline allene are shown for the first time along with optical constants, band strengths, and absorption coefficients. We also report a density and refractive index (670 nm) for each form of solid allene. A radiation-chemical experiment on allene’s formation is described, as are some applications and suggestions for future work.