Deciphering the Rotational Spectrum of the First Excited Torsional State of Propylene Oxide

TL;DR

This study investigates the first excited torsional state of propylene oxide across a broad frequency range, providing detailed spectral data, rotational constants, and potential barriers, aiding future astrochemical and molecular research.

Contribution

It offers the first comprehensive analysis of the excited torsional state of propylene oxide, including spectral line lists, rotational parameters, and comparison with quantum calculations.

Findings

Determined the potential barrier height to internal rotation as 894.5079(259) cm^{-1}.

Provided a dense line list for the first excited torsional state in the (sub-)millimeter range.

Compared experimental results with quantum chemical calculations and literature data.

Abstract

The first excited torsional state of the chiral molecule propylene oxide, $\mathrm{CH_{3}C_{2}H_{3}O}$, is investigated from millimeter up to sub-millimeter wavelengths (75-950 GHz). The first excited vibrational mode of propylene oxide, $\upsilon_{24}$, is analysed using the programs ERHAM and XIAM. Rotational constants and tunneling parameters are provided, and a description of the A-E splittings due to internal rotation is given. Furthermore, the potential barrier height to internal rotation $V_{3}$ is determined to be $V_{3} = 894.5079(259) \mathrm{cm^{-1}}$ . Our results are compared with quantum chemical calculations and literature values. We present a line list of the dense spectrum of the first excited torsional state of propylene oxide in the (sub-)millimeter range. Our results will be useful for further studies of chiral molecules in vibrationally excited states, and will enable astronomers to search for rotational transitions originating from $\upsilon_{24}$ of propylene oxide in interstellar space.