Rotational spectrum simulations of asymmetric tops in an astrochemical context
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ORIGINAL PAPER
Rotational spectrum simulations of asymmetric tops in an astrochemical context Julia C. Santos1 · Alexandre B. Rocha1
· Ricardo R. Oliveira1
Received: 5 June 2020 / Accepted: 26 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
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 H2 CO, H2 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. Keywords Microwave spectroscopy · Astrochemistry · Asymmetric tops · Rotational spectroscopy
Introduction A conspicuous attribute of rotational spectroscopy consists in its capability to provide a myriad of information on the Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00894-020-04523-0) contains supplementary material, which is available to authorized users. This paper belongs to Topical Collection XX-Brazilian Symposium of Theoretical Chemistry (SBQT2019) Alexandre B. Rocha
[email protected] Ricardo R. Oliveira [email protected] 1
Instituto de Qu´ımica, Universidade Federal do Rio de Janeiro, UFRJ, Av. Athos da Silveira Ramos, 149, Rio de Janeiro, RJ 21941-909, Brazil
molecular species and its environment. Accurate gas-phase structure determinations can be obtained through the analysis of rotationally resolved molecular spectra [1], which provide insight on t
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