Lee, Seunghyun
Date: Thursday July 4, 2013
Time: 16:00
Place: ETH Science City, HIL D 10.2
Host: Jonathan Home
Trapped ion collisions with cold atoms and cold molecules
Seunghyun Lee
Raman Research Institute, Bangalore, India
Cold chemistry is an emerging field, traditionally pursued by the chemical physics and astrophysics communities, and now by ultra-cold atomic and molecular physics communities. A hydrogen atom is spectroscopically and fundamentally an important species. Alkali atoms in the first column of the periodic table share similar chemical properties of a hydrogen atom. A mixture of alkali atoms and alkali ions is an interesting system to study in cold chemistry. We have a system of Rb+ ions + cold Rb atoms + cold Rb2 molecules in a combined trap which consists of a magneto-optical trap (MOT) for 85Rb atoms and a modified linear Paul trap for 85Rb+ ions, with the common spatial overlap. We present an experiment to investigate trapped ion collisions/interactions with neutrals. As alkali ions are optically dark, in situ detection without disturbing the system is challenging. We develop a method to monitor and characterize the ion signal indirectly from the MOT atomic fluorescence. Using this method, Rb+ ion-Rb atom rate coefficient is measured and compared with a theoretically estimated value. This work is then extended to ion-molecule collision experiments. We measure the dissociation rate of cold Rb2 by a trapped Rb+ ion within the MOT recapture energy. A simple classical harmonic oscillator model for vibrational energy transfer is used for calculating the dissociation rate coefficient theoretically.
The role of trapped ions in the ion-atom-molecule mixed system has been the primary interest in these studies. The richness of high-resolution spectral signatures in cold atoms and photoassociative molecules permits access to a specific state to study collisions and chemically reactive dynamics by trapped ions, thus offering important insights and intuitions into association and dissociation process in outer space and atmosphere.