Events & Seminars > Event Details

Where:

4:00 pm
Room 304, Chemistry Building

The Role of Low-Energy (< 20 eV) Electrons in Astrochemistry

Speaker:

Professor Chris Arumainayagam
Wellesley College

Hosted by: Professor Ian Harrison

In the interstellar medium, UV photolysis of ice mantles surrounding dust grains is thought to be the mechanism that drives the formation of “complex” molecules. The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, exceedingly penetrative high-energy cosmic rays generate secondary electrons within the clouds through molecular ionizations. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. It is the UV light, emitted by these electronically excited hydrogen molecules, that is thought to photoprocess interstellar icy grain mantles to generate “complex” molecules. In addition to producing UV light, the large numbers of low-energy (< 20 eV) secondary electrons, produced by cosmic rays, can also directly initiate radiolysis reactions in the condensed phase. The goal of our studies is to understand the low-energy, electron-induced processes that occur when high-energy cosmic rays interact with cosmic ices. Using post-irradiation temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS), we have investigated the radiolysis initiated by low-energy (5 – 20 eV) electrons in condensed methanol, ammonia, and water at ~ 90 K under ultrahigh vacuum (1×10−9 Torr) conditions. Our experimental results suggest that low-energy electron-induced condensed phase reactions may contribute to the interstellar synthesis of “complex” molecules previously thought to form exclusively via UV photons.

 

Bio sketch:

Professor Chris Arumainayagam, who has been on the faculty at Wellesley College since 1990, received his B.A. degree from Harvard University and his Ph.D. from Stanford University. One goal of Professor Arumainayagam’s research, which currently involves 15 undergraduate students, is to use surface science techniques and low-energy electron beams to understand how high-energy particles and photons interact with matter, causing ionization. His research continues to receive international recognition, as evidenced by lectures in Canada (2010), China (2010), Germany (2010), Iceland (2012), Greece (2013), and Netherlands (2014). He is a recipient of the Henry Dreyfus Teacher-Scholar award from the Camille and Henry Dreyfus Foundation. He was awarded the Anna and Samuel Pinanski Teaching Prize in 2014 by Wellesley College.