OBSERVATION OF A NON-THERMAL ORTHO-TO-PARA RATIO OF ${\Pi_{3}}^{+}$ IN HYDROGEN PLASMAS

$^{1}$M. Quack. Molec. Phys, 34, 477, 1977.Author Institution: University of Chicago, Chicago, IL 60637.; L'Universite des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, France.Although the extremely slow conversion between different nuclear spin modifications of molecules in radiative and collisional processes has been well-established, no observation of non-thermal ratios of spin modifications has been reported except for $H_{2}$ and its isotopic species. We have studied the $\nu_{2}$ fundamental band of $H_{3}^{+}$ using normal and para $H_{2}$ as the source gases to see if we could detect a different ortho-to-para ratio of ${H_{3}}^{+}$. The reaction$\[ H_{2} + H_{2}^{+} \to H_{3}^{+} + H \]$ generates only para ${H_{3}}^{+}$ if para-$H_{2}$ is $used^{1}$, and the subsequent proton hop reaction $\[ H_{3}^{+} + \bar{H}_{2} \to \bar{H}_{2}H^{+} + H_{2} \]$ will retain para-${H_{3}}^{+}$ while the hydrogen exchange reaction $\[ H_{3}^{+} + \bar{H}_{2} \to H_{2}\bar{H}^{+} + H\bar{H}\]$ is expected to convert $para-{H_{3}}^{+}$ to $ortho-{H_{3}}^{+}$. We have used two pairs of transitions, $R(4,3)^{-}$ and $R(4,4)^{-}$ separated by $0.13 cm^{-1}$ and $R(1,0)^{+}$ and $R(1,1)^{+}$ separated by $0.32 cm^{-1}$, for measurements of relative intensities. A clear difference in the intensity ratios of the ortho and para lines was detected depending on whether normal or $para-H_{2}$ was used. The ion-neutral chemical kinetics will be discussed to explain the observed results