Knowledge Bank

The results of a pressure broadening experiment in the CO - He system in the region between 1.8 - 4.2 K will be described. It was found that the pressure broadening parameters varied from 21.3 MHz/Torr to 40.0 MHz/Torr over this temperature region. Comparison with earlier theoretical calculations showed excellent agreement near 4 K; however, at the lowest observed temperature the theoretical value was about 20% greater than the measurement. In addition, we have also observed $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH3F$ pressure broadened by He. As expected from its larger dipole moment, very large signals are observed, confirming the expectation of the generality of the collisional cooling technique. Because this species is a symmetric top, effects associated with the K structure can be studied, including rotational cooling. Preliminary observations show a significant variation in the pressure broadening parameter with quantum number at 4 K.