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Design007-Jan2020

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JANUARY 2020 I DESIGN007 MAGAZINE 39 During a chemical reaction, the molecules involved in the reaction gain energy until they reach a "point of no return" known as a transition state. Until now, no one has glimpsed this state, as it lasts for only a few femtosec- onds (quadrillionths of a second). However, chemists at MIT, Argonne National Labora- tory, and several other institutions have now devised a technique that allows them to determine the structure of the transition state by detailed observation of the prod- ucts that result from the reaction. "We're looking at the consequences of the event, which have encoded in them the actual structure of the transition state," says Robert Field, the Robert T. Haslam and Bradley Dewey Professor of Chemistry at MIT. In a paper published in 2015, Field and his colleagues used laser spec- troscopy to characterize the tran- sition state for a different type of reaction known as an isomerization, in which a molecule undergoes a change of shape. In their new study, the researchers explored another style of reaction, using ultraviolet la- ser radiation to break molecules of vi- nyl cyanide into acetylene and other products. Then, they used millimeter- wave spectroscopy to observe the vibrational level population distribu- tion of the reaction products a few mil- lionths of a second after the reaction occurred. Using this technique, the researchers were able to de- termine nascent populations of molecules in different lev- els of vibrational energy—a measure of how much the at- oms of a molecule move relative to each other. Research- ers are now using this technique to study the reaction products of the pyrolytic breakdown of acetone. This also allowed the researchers to distinguish be- tween two slightly different products of the reaction — hy- drogen cyanide (HCN), in which a central carbon atom is bound to hydrogen and nitrogen, and hydrogen isocya- nide (HNC), in which nitrogen is the central atom, bound to carbon and hydrogen. (Source: MIT) Chemists Glimpse the Fleeting Transition State of a Reaction Bob Tise Matt Stevenson layout project. PCB layout is not rocket science (well, some- times it actually is). Apply- ing a few best practices, and using common sense steps in the design phase, can be a serious time saver. It is like the old adage about health: An ounce of preven- tion is worth a pound of cure. There are many resources available to help you be successful, from YouTube videos to col- leagues and your PCB manufacturer, to name a few. Good luck out there! DESIGN007 Bob Tise is an engineer at Sunstone Circuits, and Matt Stevenson is the VP of sales and marketing. To read past columns or contact Tise and Stevenson, click here.

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