Observation of a nonthermal ortho-to-para ratio of H{sub 3}{sup +} in hydrogen plasmas: Spin selection rules in plasma chemistry

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:437213

Uy, D; Dickson, R M; Kerr, K E ^[1]

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1. Univ. of Chicago, IL (United States); and others

Last year at this conference, the authors reported the observation of a nonthermal nuclear spin distribution of H{sub 3}{sup +} in hydrogen plasmas. Positive column and hollow cathode discharges with 100% parahydrogen as the source gas produced an H{sub 3}{sup +} ortho-to-para ratio of about 3:2 instead of the usual 1:1. Observing H{sub 3}+ enriched in the para modification when para-H{sub 2} is used proves that the nuclear memory is kept even after a chain of ion-neutral reactions. The selection rules based on permutation symmetry are the most robust ones in spectroscopy and collisional interactions and are not broken except in near degenerate cases. The reaction H{sub 2} + H{sub 2}{sup +} {r_arrow} H{sub 3}{sup +} + H will produce only para H{sub 3}{sup +} if both reactants are para, but a combination of ortho and para reactants would produce ortho and para H{sub 3}{sup +}. The authors have formulated a group theoretical method adapted from Quack`s paper to determine the branching ratios of chemical reactions according to the nuclear spin species of the reactants. The method is also applicable to subsequent hydrogen exchange reactions involving H{sub 3}{sup +}. Using steady-state rate equations in which the spin modification is explicity stated, an H{sub 3}{sup +} ortho-to-para ratio was calculated which approximately explains the experimental value. The group theoretical method for determining spin modification branching ratios as well as the ion-neutral chemical kinetics will be presented.

• OSTI ID: 437213
• Report Number(s): CONF-9606118--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CATIONS
CHEMICAL REACTION KINETICS
GROUP THEORY
HYDROGEN COMPOUNDS
ISOMER RATIO
MATHEMATICAL MODELS
PLASMA
PLASMA DIAGNOSTICS
SPIN