Integrated Molar Absorptivity of Mid- and Far-Infrared Spectra of Glycine and Other Selected Amino Acids.

Abstract

A selection of five proteinogenic amino acids-glycine, isoleucine, phenylalanine, tyrosine, and tryptophan-were studied in the mid-infrared and in the far-infrared with the purpose to facilitate the search and identification of these astrobiologically and astrochemically relevant molecules in space environments. The molar extinction coefficients (ɛ) of all mid- and far-infrared bands were determined as well as the integrated molar absorptivities (ψ). The mid-infrared spectra of the five selected amino acids were recorded also at three different temperatures from -180°C to ambient temperature to +200°C. We measured the wavelength shift of the infrared bands caused by temperature; and for the most relevant or temperature-sensitive infrared bands, a series of linear equations were determined relating wavelength position with temperature. Such equations may provide estimates of the temperature of these molecules once detected in astrophysical objects; and with the reported values of ɛ and ψ, it will be possible to estimate the relative abundance of these molecules in space environments.