The recent availability of semiconductor light sources in the THz and far-IR domain (1–30 THz/15–300 µm) offers many sensing opportunities for in situ and time-resolved gas-phase rotational spectroscopy of multiple species. In this short communication, a survey of the species in the HITRAN database is conducted to identify molecules with a favorable rotational spectrum relative to the infrared vibrational spectrum. Recent selected demonstrations are highlighted, showing that THz rotational spectroscopy can complement existing infrared and ultraviolet laser diagnostics, with potential for superior performance in many cases.
A proposed solar radiation management (SRM) strategy involves the injection of aerosol into Earth’s stratospheric layer, also referred to as climate intervention (CI). Calcite (CaCO3) is a key aerosol candidate within current SRM/CI climate modeling research. In this work, the infrared absorption spectra of calcite nano (50–120 nm diameter) and coarse-ground (200–750 nm diameter) particles were measured using transmission through dilute pellets (KBr and BaF2 substrates) and extinction of calcite aerosol (30–2000 nm diameter) using Fourier transform spectroscopy (FTIR). Powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM) were used to characterize sample crystallinity and morphology. The infrared absorption spectrum of aragonite, a less stable CaCO3 polymorph and common calcite impurity, was measured as part of this work. For comparison, calcite infrared spectra were also measured using attenuated total reflectance (ATR) spectroscopy. The calcite spectrum used in previous modeling studies, obtained using a spectral reflection method, is discussed. The present results are intended for use in radiative transfer model simulations.
