Low Temperature Molecular Collisional Dynamics

In some cases within the interstellar medium, it is important to understand the low-temperature cooling of molecules not by purely radiative processes, which are relatively well-understood and well-modeled, but also by state-selective gas-phase collisions. In some cases, this can be modeled in a purely theoretical way, however, it remains a significant challenge for most systems and even impossible in some cases. It is thus important that laboratory experiments are used to either verify theory for challenging cases, or to provide the sole source of data for the impossible cases.

The most common way to study this in the laboratory is to prepare a well-defined gaseous mixture of a molecule of interested that is diluted in another gas in a well-conditioned environment, and to analyze the line profiles of its pure rotational spectrum as a function of a range of temperatures and pressures appropriate to interstellar conditions. For stable molecules, and stable collisional partners, this can be routine work. For unstable molecules, this can be nearly impossible.

We are also exploring the possibility of using the CP-FTS (Chirped-Pulse Fourier Transform Spectrometer) to more efficiently study collisional cooling, by taking advantage of its fast, broadband pump-probe ability. The significant advantage of this technique is that it could be applied to both stable and unstable species alike, thus paving the way for filling in significant gaps of data.

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