High Level Ab Initio Energetic and Spectroscopic Properties of Phosphorus-Bearing Astromolecules
The successful identification of new molecules in interstellar environments relies on accurate descriptions of their energetic and spectroscopic properties. For computational methods to aid in identification, additional components to a molecule’s wavefunction, not generally included, are often required to accurately describe the systems at the highest levels, especially as increasingly heavier elements are considered. Unfortunately, the dramatically increased computational time and resources required to calculate these components all together makes it impractical for conventional computational methods. However, by starting with a high level description from conventional calculations, additional components to the energy can be additively included to produce a more complete understanding of molecular properties with fewer resources and less time than from a conventional approach. High level ab initio studies utilizing these so called composite methods have been performed on several potential phosphorus-bearing and isovalent astromolecules. To ensure completeness, all possible arrangements of the [P,N,C,O], [P,N,C,S], [Si,P,S], and [Si,N,S] sets of isomers were investigated to find the energetically lowest structures. Molecular structures, harmonic frequencies, vibrationally independent rotational constants, and electronic energies are reported for over 30 arrangements found from these isomers. Heats of formation and bond dissociation energies were calculated for the lowest energy isomers using highly accurate descriptions obtained from a composite approach. Extending the composite approach to describe the potential energy surface near the equilibrium geometry, spectroscopic constants were calculated for the lowest energy [Si,P,S] isomer and the linear PCS molecule and anion. Rotational constants, with and without vibrational dependence, harmonic and anharmonic frequencies, dipole moments and derivatives, along with first order centrifugal constants and quartic centrifugal distortion constants, when available, are reported. All values presented herein are the best available for the species studied as all previous calculations have been limited to only low level and no experimental data is available. The results of this work will aid in the identification of new molecules in astrophysical environments and guide the development of accurate descriptions of molecular properties.
Wasserman, Purdue University.
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