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D. R. WILLEY, R. E. TIMLIN JR., J. M. MERLIN, M. M. SOWA AND D. M. WESOLEK, Department of Physics, Allegheny College, Meadville, PA 16335.
We have completed low temperature pressure broadening studies of NH3 inversions transitions for broadening by He and molecular hydrogen. Pressure broadening of the (J, K) = (1, 1), (2, 2) and (3, 3) inversion transitions of NH3 by He, normal- H2 and para- H2 has been observed from 10 to 40 K. We find that the He cross sections are the smallest followed by the para- H2 cross sections which are two to five times larger with the normal- H2 cross sections being two to ten times larger than for He. In addition, we have used ab initio potential surfaces to calculate He and para- H2 cross sections for comparison with our experimental data.