Knowledge Bank

We report low temperature helium pressure broadening cross sections of $NH3$ inversion transitions from a collisionally cooled experiment. Helium pressure broadening data was obtained for the three microwave inversion transitions of the $(J.K)$ rotational levels, (1 1), (2,2) and (3.3), over a temperature of 10-35 K. Pressure broadening cross sections were also calculated for comparison with the experimental data using three existing $NH3-He$ potential surfaces. The agreement between experiment and theory is not particularity good, especially for the ortho-$NH3$ level, (3,3), and appears to point out the need for further work in either the description of the potential surface or the modeling of the collision dynamics.