A prochiral precursor in space? Accurate laboratory characterization of acetylacetylene in the cm-wave region

The most prominent pure rotational transitions of the prochiral, possibly prebiotic molecule acetylacetylene are recorded in the frequency range of 6.5-26.5 GHz for a reliable spectral characterization prerequisite to a possible extraterrestrial observation. Therefore, three different approaches for global fitting of the vibrational ground state are applied to analyze the experimentally determined transition frequencies using the programs SPFIT, XIAM and ERHAM corresponding to different theoretical treatments solving the internal rotation problem. Furthermore, the resulting internal rotation parameter V3 is compared to those other substituted acetyl species, and derivatives of butynes and possible explanations for the observed trends are given. For the substituted acetyl species, the spectra of acetylfluoride, -chloride, -bromide and -iodide are reanalyzed. The obtained rotational constants have been interpreted in terms of characterizing the geometric structure. A correlation between the tunneling parameter epsilon 1 and V-3 of several molecular species displaying spectral internal rotation splitting patterns has been found and quantified. This relationship can simplify the analysis of vibrational ground state rotational spectra in finding a suitable starting point for the fitting procedure using the program ERHAM, which is the predestined choice to analyze and predict signal positions up to very high quantum numbers. Being able to predict those signal positions is crucial for a possible comprehensive astronomical identification and subsequent application as an astrophysical probe for the conditions in interstellar molecular clouds. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study focuses on the pure rotational transitions of acetylacetylene molecule and applies different methods to globally fit the vibrational ground state for spectral characterization. The resulting internal rotation parameter is compared with other substituted acetyl species, and relationships between various molecular species displaying spectral internal rotation splitting patterns are quantified. The ability to predict signal positions is crucial for comprehensive astronomical identification and application as an astrophysical probe.