  We present an experimental instrument that performs laboratory-based
gas-phase Terahertz Desorption Emission Spectroscopy (THz-DES) experiments in
support of astrochemistry. The measurement system combines a terahertz
heterodyne radiometer that uses room temperature semiconductor mixer diode
technology previously developed for the purposes of Earth observation, with a
high-vacuum desorption gas cell and high-speed digital sampling circuitry to
enable high spectral and temporal resolution spectroscopy of molecular species
with thermal discrimination. During use, molecules are condensed onto a liquid
nitrogen cooled metal finger to emulate ice structures that may be present in
space. Following deposition, thermal desorption is controlled and initiated by
means of a heater and monitored via a temperature sensor. The 'rest frequency'
spectral signatures of molecules released into the vacuum cell environment are
detected by the heterodyne radiometer in real-time and characterised with high
spectral resolution. To demonstrate the viability of the instrument, we have
studied Nitrous Oxide (N2O). This molecule strongly emits within the terahertz
(sub-millimetre wavelength) range and provide a suitable test gas and we
compare the results obtained with more traditional techniques such as
quadrupole mass spectrometry. The results obtained allow us to fully
characterize the measurement method and we discuss its potential use as a
laboratory tool in support of astrochemical observations of molecular species
in the interstellar medium and the Solar System.
