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THE J=0 HYDROGEN MOLECULE AS A COLLISION PARTNER

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Title: THE J=0 HYDROGEN MOLECULE AS A COLLISION PARTNER
Creators: Rao, D. Ramachandra; Oka, T.
Issue Date: 1980
Abstract: It is expected theoretically that a hydrogen molecule in the J=0 rotational level would behave differently as a collision partner from those in the other rotational levels. This is because it effectively does not possess a quadrupole moment and thus does not exert a long range force. In order to demonstrate this point experimentally, the pressure broadening of the $\nu_{1}$ band of $NH_{3}$ by $H_{2}$ has been measured using a difference frequency laser system. The difference in the percentage of the J=0 $H_{2}$ in normal-$H_{2}$ and para-$H_{2}$ (18.4% versus 73.2% at dry ice temperature) was exploited to distinguish the effect of the J=0 $H_{2}$ from that of the rest. The measurement, has shown that the normal-$H_{2}$ is more effective as a perturber than the para-$H_{2}$ by a factor or $1.29\pm 0.03$ at dry ice temperature. Using the simple assumption that all $J\neq0 H_{2}$ has the same collision cross section, it was found that $\sigma(J\neq 0)$ is larger than $\sigma (J=0)$ by about 60%. The variation of $\sigma(J=0)$ and $\sigma(J\neq0) - \sigma(J=0)$ with temperature has also been determined. The astrophysical implications of the result will be discussed.
URI: http://hdl.handle.net/1811/11431
Other Identifiers: 1980-TH-1
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