The Formation and Detection of Biogenic Aromatics in Dense Molecular Clouds around Embedded Protostars

Grant #: NNX13AJ08G
Senior Scientist: Alessandra Ricca

ice grain illustration

Much of the material in the interstellar medium is concentrated in large molecular clouds. Molecules can be formed in these clouds by ion-molecule, gas-phase reactions, and solid-state reactions in and on icy grains. The UV radiation in the cloud drives a rich photochemistry of the molecules frozen on the grains particularly in star-forming regions and along the edges of their planet-forming disks. This produces complex species in the ices, many of biogenic interest. Ultimately, these biogenic compounds become incorporated into materials that make up new stars, planets, satellites, asteroids, and comets. Thus, these are some of the raw materials that contributed to the origin of life. It is the purpose of this proposal to start to understand the role that the widespread and abundant polycyclic aromatic hydrocarbons (PAHs) played in this process.

Given that H2O ice is widespread throughout interstellar clouds, planet forming disks, comets, and icy planets and satellites and that PAHs are abundant and ubiquitous in all regions where these ices form, the answers to the following questions are critical to developing a fuller understanding of the role interstellar ice photochemistry played in the origin of life:

  • How are hydroxylated and oxygenated PAHs (aromatic alcohols and quinones) produced abiotically in dense molecular clouds?  What mechanisms dominate the processes and which products are preferentially formed?
  • How is reactivity with other ice species affected by PAH size, electronic state, and charge?
  • How does the H2O ice environment affect the optical and infrared spectra of the reactants and products?
  • How would the presence of PAHs and their photoproducts influence the spectra of dense clouds?