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July 2012 Print

Musa Ahmed, Senior Scientist, Chemical Dynamics Beamline


musa ahmedAt more than 17 years old, the Chemical Dynamics Beamline (ALS Beamline 9.0.2) is one of the oldest beamlines at the ALS. Over those years, the scientific thrusts at the beamline have evolved from performing state-of-the-art reaction dynamics studies to probing and understanding the physical and chemical principles that govern complicated phenomena in nature. Strongly coupled with this interest is a realization that research should be guided by the grand scientific challenges of the 21st century. Gaining a molecular level understanding of alternative carbon neutral energy sources and how to mitigate the effects of global climate change are themes that currently drive a number of users and beamline staff.

The beamline has four terminals—two with monochromators—which deliver vacuum ultraviolet light in the range of 7.4-25 eV. A number of endstations, all configured with mass spectrometers, measure and quantify processes which are relevant to a broad range of fields, particularly combustion and aerosol science, electronic structure of radicals, molecules and clusters in the gas phase and analysis of complicated systems, such as bacterial biofilms, atmospheric aerosols, fossil feathers and soil. Four of the endstations dedicated to molecular beams, aerosol studies, low-temperature reaction studies and imaging mass spectrometry are in-house facilities. Two "roll-up" endstations come from the Sandia Livermore combustion research facility where flame chemists and reaction kineticists probe complex molecules in exquisite detail and discover species never seen before using synchrotron radiation (see ALS Science Highlight "Direct Kinetic Measurements of a Criegee Intermediate"-ed.) . The home team, comprising students, post-docs and scientists discover the “glassy” nature of an organic aerosol, decipher the transfer of protons in the absence of hydrogen bonds (see this month's highlight,  "A Surprising Path for Proton Transfer Without Hydrogen Bonds"-ed.) , and use lasers to blow sand and graphite up  to get them into the gas-phase. In collaboration with outside users, the origin of the solar system is elucidated, the effects of cigarette smoke on walls quantified, and the nature of formation of organic molecules in distant Titan explained. Theoretical chemists can be seen working the owl shift, seeking to understand what happens when molecules relevant to biofuel production are heated to 1300 Celsius. Evolutionary biologists, paleontologists, environmental geochemists, and life science type folks have put 47-million-years-old bird feathers, dirt, pieces of wood, grass and leaves, and scum floating on top of a pond into the beautiful imaging mass spectrometer located right by the experimental walkway. Sometimes an old biodiesel running Mercedes can be seen in the parking lot outside, belching its exhaust into the synchrotron for study, and that is what the chemical dynamics beamline is all about. Seventeen years old and marching boldly on.

For more information about Musa and his team, and their research, visit the Beamline 9.0.2 Web site.