Knowledge Bank

We have recently shown that collisions with cold He molecules can be used to cool, under essentially equilibrium conditions, gas phase molecules to very low $temperatures1$. The technique is especially advantageous for spectroscopy in the millimeter and submillimeter spectral region. In this region $h\nu >kT$ for very low temperatures and the number of open collisional channels is greatly reduced, thereby simplifying both theoretical calculations and the interpretation of experimental data. The technique is very general, produces strong signals of narrow linewidth, and is applicable to any stable species that is ordinarily studied in this spectral region. In this talk we will describe a new apparatus that we have recently constructed. This new system allows studies at variable temperatures (from the temperature of pumped liquid He up to ambient temperature) and is improved cryogenically from the earlier version. Results from pressure broadening experiments will be described. In addition, its application to the study of weakly bound species, collisional processes in general, and for the purposes of simplifying complex spectra will be discussed.