Pressure broadening of the J=5←4 transition of carbon monoxide from 17 to 200 K: A new collisional cooling experiment

A new spectroscopic experiment has been constructed at the Jet Propulsion Laboratory. This experiment employs the collisional cooling technique to study gases at temperatures below their condensation points. Specifically, the experiment has been designed to mimic the temperatures of the interstellar medium for the study of water under these conditions. The ultimate purpose is to measure state-to-state excitation rates under equilibrium conditions to provide insights into the interpretation of interstellar water spectra obtained from space-borne platforms such as the Herschel Space Observatory. This paper presents an overview of the new experiment including a discussion of its design and a detailed explanation of the system. In addition, we report a pressure broadening study of the J=5←4 transition of CO at 576 GHz used as a system validation. The new results are compared with measurements from the literature as a validation of the new experiment. In addition, the non-classical behavior of the pressure broadening of CO at low temperature observed in the measurements will be discussed.