High Resolution Mid-Infrared Spectroscopy of Cold, Complex Molecules

Abstract

Progress in the detection of molecules in interstellar environments is advanced by stateresolved laboratory spectroscopy of the candidate molecules. Gas-phase precision spectroscopy is challenged, however, by the size and complexity of the probed molecules. This paper outlines the construction, testing, and application of a mid-infrared (IR) cavity-enhanced frequency comb spectrometer for measurement of complex molecules cooled to cryogenic temperatures through collisions with helium buffer gas. The instrument sources 6-11 µm comb light, and spectra are measured using a Fourier transform spectrometer. The molecules here measured garner interest both as spectroscopic problems as is the case of ethanol, a model of the interactions between large-amplitude internal motions in a nonrigid molecule, and as astrochemical problems as is the case of naphthalene and acenaphthene, both polycyclic aromatic hydrocarbons (PAHs) that may be identified in interstellar environments. High-resolution mid-IR spectra of these molecules are presented and fit to model Hamiltonians.