Knowledge Bank

A new system has been developed which makes possible the measurement of the helium pressure broadening parameters of $CH3F$ and $H2S$ between approximately 1K and 100K. This apparatus is based on a continuously filled helium pot which is separate from the main helium reservoir and whose temperature can be varied over the 1K to 100K region by control of the pumping speed on the pot. In combination with other experimental systems, this has allowed measurements over the entire 1K to 1000K range. This range is wide enough to clearly observe the transition from the high temperature semiclassical regime in which the physics of the collision is properly described by Anderson-like theories to a low temperature regime in which new phenomena associated with quasibound states requires a more complete quantum mechanical description. Experimental results and their relationship to theoretical predictions will be discussed. Similarities and differences with the results of hydrogen pressure broadening discussed in the next talk will also be presented.