Our work on rotational spectroscopy of methyl-tert butyl ether (MTBE) is now published in PCCP (https://doi.org/10.1039/D4CP00797B). This paper presents the technical details of our Ka-band CP-FTMW spectrometer and its application to MTBE. Initially we obtained this sample by mistake, as another unit on campus had mistakenly received the wrong solvent in an order they had placed. Because it had a high vapor pressure and a potentially interesting rotational spectrum, which had only been reported in the 9-18 GHz frequency range before, we decided to use it to test the performance of our instrument. As it turns out, the spectrum was especially interesting owing to its extreme near-prolate nature. We were able to observe a torsionally excited state of MTBE for the first time, and our analysis suggests that the b and c inertial axes actually exchange relative to the ground state, which is a rare phenomenon. See the paper for the full details and analysis! You can interactively view the spectral data at https://mtbe-data.streamlit.app/.
