15min:

DANIEL R. WILLEY, P. DENARDO, P. NULL, P. PONDILLO AND T. TYSZKA, Department of Physics, Allegheny College, Meadville, PA 16335.

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 range 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 particularily 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.