The interstellar medium (ISM) is full of rich chemistry that we as astrochemists are only beginning to understand. The Crabtree group is interested in using rotational spectroscopy to provide a spectrum, or molecular “fingerprint,” for future observational studies. Our characterization instrument is equipped to measure the rotational spectrum of polar molecules from 6 - 18 GHz. Astronomers can use our data to search for new molecules in space, and we can also use the data to perform additional low-temperature kinetics studies in our CRESU experiment.
To perform our characterization studies, we designed and custom built a segmented Chirped Pulse Fourier Transform Microwave (CP-FTMW) spectrometer. Our motivation to build this instrument is to have a low-cost alternative to the microwave spectrometers equipped with high-speed digital oscilloscopes, arbitrary waveform generators, and TWT amplifiers. Our system is ideal for creating radicals, which are interesting because of their highly reactive nature and relevance to space. Furthermore, CP-FTMW spectroscopy is a highly effective technique in identifying exotic molecules produced in the complex plasma created by our high voltage discharge source because of its inherent sensitivity to slight differences in molecular geometry. Our microwave circuit is based on a direct digital synthesizer (DDS) that outputs a 1 GHz “chirp” that is tunable across our desired 6 - 18 GHz range. This microwave circuit is used to probe molecules generated in the plasma discharge. For further identification of our radicals we have constructed a set of Helmholtz coils centered around the reaction region of our vacuum chamber. Due to the Zeeman effect, radicals are affected by the Earth’s magnetic field, thereby necessitating the need for Helmholtz coils to cancel the Earth’s magnetic field, thus providing a more accurate rotational spectrum.