Rotational spectroscopy of isotopic oxirane, $c$-C$_2$H$_4$O

TL;DR

This study measured the rotational spectra of oxirane isotopologs to aid astronomical detection and evaluated different spectral reduction methods for asymmetric molecules.

Contribution

It provides detailed spectral data for oxirane isotopologs and assesses the performance of Watson's A and S reductions in spectral fitting.

Findings

A reduction in the I$^r$ representation required fewer parameters.

The A reduction in the III$^l$ representation did not fit well.

Other reduction combinations yielded similar satisfactory fits.

Abstract

We studied the rotational spectrum of oxirane in a sample of natural isotopic composition in selected regions between 158 GHz and 1093 GHz. Investigations of the isotopologs with one $^{13}$C or one $^{18}$O were the primary focus in order to facilitate searches for them in space. We also examined the main isotopic species mainly to look into the performance of Watson's A and S reductions both in an oblate and in a prolate representation. Even though oxirane is a rather asymmetric oblate rotor, the A reduction in the III$^l$ representation did not yield a satisfactory fit, as was observed frequently earlier for other molecules. The other three combinations yielded satisfactory fits of similar quality among each other; the A reduction in the I$^r$ representation required two parameters less than both S reduction fits.