Cyclopropenyl cation – the simplest Huckel's aromatic molecule – and its cyclic methyl derivatives in Titan's upper atmosphere

Baiardi

Bloino

et al. 2017

To gain information on the abiotic synthesis of the building blocks of life from simple molecules, and their subsequent chemical evolution to biological systems, the starting point is the identification of target species in Titan-like planets, i.e., planets that resemble the primitive Earth, as well as in Earth-like planets in the habitable zone of their star, namely planets where life can be already originated. In this scenario, molecular spectroscopy plays a crucial role because spectroscopic signatures are at the basis of an unequivocal proof for the presence of these target molecules. Thanks to the advances in many different techniques and to the NASA successful Kepler exoplanet transit mission, thousands of diverse planets outside of our solar system have been discovered. The James Webb Space Telescope (JWST), scheduled to be launched in 2018, will be very helpful in the identification of biosignature gases in Earth-like planets' atmospheres and of prebiotic molecule signatures in Titan-like atmospheres by observing their absorption during transits. While the search for key-target molecules in exoplanet atmospheres can be carried out by the JWST Transit Spectroscopy in the infrared (IR) region (0.6 - 29 µm wavelength range), opportunities for their detection in protostellar cores, protoplanetary disks and on Titan are also offered by the interferometric high spectral and spatial resolution observations using the Atacama Large Millimeter/submillimeter Array (ALMA). In the present work, target molecules have been selected and their spectroscopic characterization presented in view of supporting their infrared and complementary millimeter/submillimeter-wave spectral observations. In detail, the selected target molecules include: (1) the three-membered oxygen-containing heterocycles: oxirane and protonated oxirane, (2) the cyclopropenyl cation and its methyl derivative, (3) two examples of ortho- and peri-fused tri-cyclic aromatic rings, i.e., the phenalenyl cation (C13H9+) and anion (C13H9-), and (4) uracil, a specific RNA base.

Section: Introductionmentioning

confidence: 99%

Spectroscopic Characterization of Key Aromatic and Heterocyclic Molecules: A Route toward the Origin of Life

Baiardi

Bloino

et al. 2017

“…The great interest in Titan’s atmosphere is due to the fact that recent measurements (Niemann et al 2002; Waite et al 2004; Young et al 2004) revealed that Titan’s atmosphere is characterized by a rich and complex organic chemistry (see Ali et al 2013 and references therein). This led to a further interest in Titan because the investigation of its atmosphere might shed light on the organic evolution in the atmosphere of early earth.…”

Section: Introductionmentioning

confidence: 99%

Accurate Spectroscopic Characterization of Oxirane: A Valuable Route to Its Identification in Titan's Atmosphere and the Assignment of Unidentified Infrared Bands

Biczysko

Bloino

et al. 2014

ApJ

In an effort to provide an accurate spectroscopic characterization of oxirane, state-of-the-art computational methods and approaches have been employed to determine highly accurate fundamental vibrational frequencies and rotational parameters. Available experimental data were used to assess the reliability of our computations, and an accuracy on average of 10 cm for fundamental transitions as well as overtones and combination bands has been pointed out. Moving to rotational spectroscopy, relative discrepancies of 0.1%, 2%-3%, and 3%-4% were observed for rotational, quartic, and sextic centrifugal-distortion constants, respectively. We are therefore confident that the highly accurate spectroscopic data provided herein can be useful for identification of oxirane in Titan's atmosphere and the assignment of unidentified infrared bands. Since oxirane was already observed in the interstellar medium and some astronomical objects are characterized by very high D/H ratios, we also considered the accurate determination of the spectroscopic parameters for the mono-deuterated species, oxirane-1. For the latter, an empirical scaling procedure allowed us to improve our computed data and to provide predictions for rotational transitions with a relative accuracy of about 0.02% (i.e., an uncertainty of about 40 MHz for a transition lying at 200 GHz).

“…The study of Titan’s atmosphere has attracted great attention due to recent measurements that revealed Titan’s atmosphere to be characterized by a rich and complex organic chemistry (see Ali et al 2013 and references therein). Furthermore, Titan is thought to represent a model of primitive Earth because its atmosphere contains significant quantities of carbon (~2% CH 4 ) and nitrogen (98% N 2 ), and traces of oxygen (~50 ppm CO; Raulin et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Accurate Spectroscopic Characterization of Protonated Oxirane: A Potential Prebiotic Species in Titan's Atmosphere

Ali

Biczysko

et al. 2014

ApJ

An accurate spectroscopic characterization of protonated oxirane has been carried out by means of state-of-the-art computational methods and approaches. The calculated spectroscopic parameters from our recent computational investigation of oxirane together with the corresponding experimental data available were used to assess the accuracy of our predicted rotational and IR spectra of protonated oxirane. We found an accuracy of about 10 cm for vibrational transitions (fundamentals as well as overtones and combination bands) and, in relative terms, of 0.1% for rotational transitions. We are therefore confident that the spectroscopic data provided herein are a valuable support for the detection of protonated oxirane not only in Titan's atmosphere but also in the interstellar medium.