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D. R. WILLEY, R. E. TIMLIN, M. DERAMO, P. L. PONDILLO, D. M. WESOLEK AND R. W. WIG, Department of Physics, Allegheny College, Meadville, PA 16335 .
Pressure broadening of the (J, K) = (1, 1), (2, 2) and (3, 3) inversion transitions of NH3 was measured using normal- H2 as the broadening agent at kinetic temperatures of 15 to 40 K. Measurements were taken in a quasi equilibrium cell using the collisional cooling technique. H2 pressure broadening cross sections were compared to low temperature He pressure broadening of the same transitions and found to be from 2.5 to 8 times larger than corresponding He cross sections. Measured normal H2 and He cross sections were also compared to calculated J = 0, para- H2 cross sections. Preliminary experimental results for broadening by para- H2 will also be presented.