TIME-RESOLVED MW-MW STUDIES OF LOW TEMPERATURE $NH_{3}$ - He COLLISIONS

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 Title: TIME-RESOLVED MW-MW STUDIES OF LOW TEMPERATURE $NH_{3}$ - He COLLISIONS Creators: Willey, D. R. Issue Date: 2004 Publisher: Ohio State University Abstract: We report preliminary results of low temperature (10 - 40 K) experimental studies of $NH_{3}$ in collisions with He using time-resolved MW - MW techniques. In these studies, ammonia is collisionally cooled in a low temperature cell filled with a background of helium. A short $(< 1 \mu s)$ pump pulse is used to excite a particular $(J, K)$ inversion pair while a second weak source probes nearby inversion transitions. At these low temperatures, however, only a few rotational levels are populated, greatly simplifying the interpretation of the time-resolved data. In fact for para - $NH_{3}$ only the (1, 1) and (2, 2) levels will have significant population at 10 - 40 K. Adding in the inversion doublets, para - $NH_{3}$ is effectively a four-level system at these temperatures, making it in principle feasible to extract approximate state-to-state collision rates. Description: Author Institution: Department of Physics, Allegheny College URI: http://hdl.handle.net/1811/21171 Other Identifiers: 2004-FD-10