Laboratory measurements of three deuterium substitution reactions important in interstellar chemistry

Columbia University, New York NY

Investigators

Abstract

The extremely cold and tenuous clouds of gas and dust that occupy interstellar space -- the space between the stars -- host a rich chemistry. This research project will study chemical reactions of the simplest polyatomic molecular ions that drive the chemistry of the interstellar gas. These ions can exist at the very low temperatures at which most other molecules freeze out. The research team will use a sophisticated laboratory experiment to accurately determine reaction rates of the ions at very low temperatures. Results from the study will allow astronomers to better understand the abundance of these ions in space and to use them as probes of the coldest and densest regions within interstellar clouds, which are birthplaces of stars and planets. The project will contribute to the training and professional development of a postdoctoral scholar. The project will also support a program that is known to have a positive impact on middle school and high school science education. The research team will perform laboratory studies of the gas-phase reactions of atomic deuterium with H3+ -- the simplest polyatomic ion found in the interstellar gas -- and its deuterated forms H2D+ and D2H+. The three reactions are important in the chemistry that drastically increases the deuterium content of interstellar molecules; and the H2D+ and D2H+ ions probe the densest regions of cold dark clouds where most other molecules freeze out. Understanding the chemistry of these ions is therefore essential to understanding these regions, which are potential sites of star and planet formation. The proposed studies are challenging because atoms and molecular ions are difficult to produce in the laboratory. The team will measure rate coefficients of the reactions of D atoms with H3+, H2D+, and D2H+ using a dual-source, merged fast-beams apparatus, which was built with prior NSF support (AST-0905832), that enables them to produce and react beams of atoms and molecular ions. Collisional cross sections extracted from the measured rate coefficients will be used to generate thermal rate coefficients at temperatures relevant to cold interstellar clouds (10 K - 100 K). The rate coefficients are expected to be accurate to within 15% -- about an order of magnitude better than those calculated for the three reactions. The project will support a postdoctoral scholar at Columbia University. The project will also allow team members to continue participating in the Columbia University Summer Research Program that engages middle school and high school teachers in scientific research, and has been shown to help retain teachers in school and improve student performance in science courses.