Hunting for interstellar molecules: rotational spectra of reactive species

Abstract

Interstellar molecules are often highly reactive species, which are unstable under terrestrial conditions, such as radicals, ions and unsaturated carbon chains. Their detection in space is usually based on the...

Insights into the Molecular Structure and Spectroscopic Properties of HONCO: An Accurate Ab Initio Study

“…For predicting the rotational spectrum, in addition to the rotational and centrifugal distortion constants, the components of the electric dipole moments along the inertial axes are required in order to obtain information on the type and intensity of transitions that can be observed. , Since for an accurate estimate of this property, incorporation of the diffuse function is important, its evaluation has been performed at the fc-CCSD­(T)/aug-cc-pVTZ , level of theory. Since HONCO is not a commercial molecule, very likely it needs to be produced on-the-fly while performing the measurements, thereby exploiting ad hoc techniques, such as the flash vacuum pyrolysis, , which, however, can lead to the concomitant formation of other (unwanted) species. Therefore, characteristic features in the rotational spectrum can be very useful for the identification of a molecule of interest.…”

“…40,41 Since for an accurate estimate of this property, incorporation of the diffuse function is important, its evaluation has been performed at the fc-CCSD(T)/aug-cc-pVTZ 27,42 level of theory. Since HONCO is not a commercial molecule, very likely it needs to be produced on-the-fly while performing the measurements, thereby exploiting ad hoc techniques, such as the flash vacuum pyrolysis, 43,44 which, however, can lead to the concomitant formation of other (unwanted) species. Therefore, characteristic features in the rotational spectrum can be very useful for the identification of a molecule of interest.…”

Interstellar Ices: A Factory of the Origin-of-Life Molecules

“…The outcomes are the so-called radioastronomical spectra, which are usually extremely complex because of overlapping features due to tens (or even hundreds) of molecules. Consequently, the identification of 1 in the ISM requires its accurate spectroscopic characterization in the laboratory in order to search for its fingerprints in the "radioastronomical-spectra forest" 9,10. More generally, what is the guidance toward new discoveries?…”

The performance of hybrid and F12∗/F12c explicitly correlated coupled cluster methods for use in anharmonic vibrational frequency computations

“…Hybrid methods (also called multilevel or multiresolution approaches) combining different levels of theory into different portions of the computations have shown exceptional promise in providing spectroscopically accurate reference data for some time [38][39][40][41]. Most notably, Puzzarini and coworkers [42,43] have been able to provide approaches for computing exceptionally accurate rotational constants for application to the detection of novel molecules in space. They have employed the so-called CBS+CV level of theory, using a combination of complete basis set (CBS) Hartree-Fock and coupled cluster computations with further inclusions for core-valence considerations, for determination of equilibrium rotational constants [42,43].…”

“…Most notably, Puzzarini and coworkers [42,43] have been able to provide approaches for computing exceptionally accurate rotational constants for application to the detection of novel molecules in space. They have employed the so-called CBS+CV level of theory, using a combination of complete basis set (CBS) Hartree-Fock and coupled cluster computations with further inclusions for core-valence considerations, for determination of equilibrium rotational constants [42,43]. These are, then, further augmented by lower-level computations (often from MP2 [44]) for the computations of the vibrational effects within the rotational constants stemming from the anharmonicity of the vibrational frequencies.…”