Observation of Ortho-ParaH3+Selection Rules in Plasma Chemistry

Intensity ratios of infrared spectral lines of ortho- and para- ${\mathrm{H}}_3^{+}$ have been measured in hydrogen plasmas using normal and para- ${\mathrm{H}}_2$. Large dependences of the intensity ratios on the parent gases have been observed, indicating the spin memory of protons even after chemical reactions. The results clearly demonstrate the existence of selection rules on nuclear spin modifications in chemical reactions theoretically anticipated by M. Quack [Mol. Phys. 34, 477 (1977)].