Rotational spectrum simulations of asymmetric tops in an astrochemical context

Abstract

Rotational spectroscopy plays a major role in the field of observational astrochemistry, enabling the detection of more than 200 species including a plethora of complex organic molecules in different space environments. Those line detections allow correctly determining the sources and physical properties, as well as exploring their morphology, evolutionary stage, and chemical evolution pathways. In this context, quantum chemistry is a powerful tool to the investigation of the molecular inventory of astrophysical environments, guiding laboratory experiments and assisting in both line assignments and extrapolation of the experimental data to unexplored frequency ranges. In the present work, we start by briefly reviewing the rotational model Hamiltonian for asymmetric tops beyond the rigid-rotor approximation, including rotational-vibrational, centrifugal, and anharmonic effects. Then, aiming at further contributing to the recording and analysis of laboratory microwave spectroscopy by means of accessible, less demanding quantum chemical methods, we performed density functional theory (DFT) calculations of the spectroscopic parameters of astrochemically relevant species, followed by their rotational spectrum simulations. Furthermore, dispersion-correction effects combined with different functionals were also investigated. Case studies are the asymmetric tops H 2 CO, H 2 CS, c-HCOOH, t-HCOOH, and HNCO. Spectroscopic parameter predictions were overall very close to experiment, with mean percentage errors smaller than 1% for zeroth order and ∼ 5% for first-order constants. We discuss the implications and impacts of those constants on spectrum simulations, and compare line-frequency predictions at millimeter wavelengths. Moreover, theoretical spectroscopic parameters of c-HCOOH and HNCO are introduced for the first time in this work.

Methyl acetylene in G331.512-0.103: Looking at massive star formation through the lens of chemistry

“…as well as its morphology and evolutionary stage (e.g., Wyrowski et al 1999;Beuther et al 2005;Guzmán et al 2018). In this context, experimental and theoretical rotational spectroscopy share a symbiotic relationship that is fundamental to broaden our percipience of the physics and chemistry of the ISM (see, e.g., Puzzarini 2017; Puzzarini and Barone 2020; Cerqueira et al 2020;Santos et al 2020). In order to understand radio observations of molecular lines and its implications on astronomical matters, it is crucial to become acquainted with rotational spectroscopy and its theoretical description.…”