COLLISIONAL NUCLEAR SPIN INTERCOMBINATION IN $NH_{3}$ OBSERVED IN SUPERSONIC JET EXPANSION BY DIODE LASER SPECTROSCOPY
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Date
1992
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Ohio State University
Abstract
The nuclear spin modifications of molecular wavefunctions are hardly changed in radiactive or collisional processes. In the present study we have found for the lower rotational levels of $NH_{3}$ experimental evidence for the nuclear spin intercombination by collision during the supersonic jet expansion; an over-population in the $(J, K) = (I, l)$ state has been observed in the jet spectra. The populations were determined by measuring the line intensities of the $v_{2}$ band of $NH_{3}$ by a diode laser spectrometer. The rotational temperature reached 9 K for 5 \% $NH_{3}$ seeded in Ar, 16 K for 10 \%, and 53 K for pure $NH_{3}$. The ratio of ortho and para concentration, which is 1:1 in room temperature, was found in the case of 10 \% $NH_{3}$ to be 0.65:1 after the cooling process by supersonic expansion.
Description
Author Institution: I. Physikalisches Institut, Universit\""{a}t zu K\""{o}ln