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Computational Quantum Chemistry Module


Image of the individual Quantum Chemistry Studies Module orange hexagon icon.This Module of the Ames team will make use of computational quantum chemistry techniques (ab initio and density functional approaches) to elucidate the detailed mechanisms of chemical reactions both in the gas and condensed phases, as well as diverse catalytic processes. Quantum chemistry results (reaction mechanisms, reaction rates, and product ratios) will be used to help interpret the laboratory results, and will feed into improved parameters for the disk modeling studies.

2016 Summary:

In conjunction with the laboratory studies of nucleobase production, we investigated the formation of nucleobases in irradiated astrophysical ices containing pyrimidine and purine using computational quantum chemistry. This work demonstrated the formation of nucleobases is energetically and kinetically favorable given the presence of one or several water molecules, i.e., it can occur in the solid state, but not in the gas phase (Fig. 2 and 3). This work also explains why some nucleobases (uracil) are made efficiently, while others (thymine) are not. In another study, electronic structure calculations were performed on C4 H3 +, C6 H3 + and C6 H5 +. C6 H5 + was found to be very stable and may be a good nucleation center for the growth of larger polycyclic aromatic hydrocarbons (PAHs), one of the most abundant families of molecules in space. We also continued our work with the Dutch Astrochemistry Network (DAN) on the computation of infrared emission from PAHs.

Fig. 2. Diagram illustrating the three reaction pathways from pyrimidine 1 to uracil 3 and thymine 6 we studied using quantum chemical computations. Fig. 3. Reaction scheme indicating the amino and hydroxyl group substitutions
on the purine molecule and pathways to the nucleobases adenine and guanine studied with quantum chemical computations.

 

Team members:

Timothy Lee

Partha P. Bera

Martin Head-Gordon

Tamar Stein