The role of low-energy (less than 20 eV) electrons in astrochemistry Christopher Arumainayagam 2 , Kennedy Barnes 1 , Qin Tong Wu 1 , James Battat 2 and Marco Padovani 3 1 Wellesley College, Department of Chemistry, 106 Central St, Wellesley, USA, 2 Wellesley College, Department of Physics, 106 Central St, Wellesley, USA, 3 INAF - Osservatorio Astrofisico di Arcetri, 5 Largo E. Fermi, Firenze, Italy Radiation chemistry and photochemistry inside the ice mantles surrounding micron-size dust grains within dark, dense molecular clouds likely dominate the synthesis of prebiotic molecules (e.g., glycine) in the interstellar medium 1 . We explore the relative importance of low-energy (<20 eV) secondary electrons — instigators of radiation chemistry — and low-energy photons (<10 eV) — instigators of photochemistry. We estimate the flux of cosmic-ray-induced secondary electrons within interstellar ices by 1) considering the attenuated cosmic-ray particle spectra after propagation through dark, dense molecular clouds and 2) incorporating data from the National Institute for Standards and Technology (NIST) databases to account for the total stopping power (the energy loss per unit length) for particles in liquid water. Photons produced via excitation of gaseous hydrogen within dense molecular clouds have a flux of ~10 3 photons cm −2 s −1 whereas our order-of-magnitude calculations indicate fluxes as high as ~10 2 electrons cm −2 s −1 for low-energy secondary electrons produced within interstellar ices due to incident cosmic rays. Furthermore, reaction cross-sections can be several orders of magnitude larger for electrons than for photons because (1) electron-induced singlet-to-triplet transitions are allowed, (2) electrons can be captured into resonant negative ion states that may then dissociate 2 (3) electron impact excitation is not a resonant process. Therefore, our laboratory studies and order-of-magnitude calculations suggest that the role of low-energy secondary electrons is at least as significant as that of photons in the interstellar synthesis of prebiotic molecules, which likely seeded Earth via comets and meteorites in a process referred to as molecular panspermia.
References 1. C. Arumainayagam, R. Garrod, M. Boyer, A. Hay, S. Bao, J. Campbell, J. Wang, C. Nowak, M. Arumainayagam, P. Hodge, Chem. Soc. Rev. 2019 , 48, 2293-2314 2. C. Aruminaygam, H. Lee, R. Nelson, D. Haines, R. Gunawardane, Surf. Sci. Rep. 2010 , 1, 1-44
P01
© The Author(s), 2023
Made with FlippingBook Learn more on our blog