Isotope effects on the populations of metastable H₃ and D ₃ molecules in neutralized ion beams

The relative abundances of metastable H*₃ and D ₃* molecules in collimated beams of neutralized ions are analyzed by the technique of collisional reionization (charge stripping). The fraction of metastable/dissociative species formed in the electron transfer process H₃⁺ (D₃⁺)+K(g) →H*₃(D*₃)+K⁺ diminishes if the precursor ions have excess internal energy. The abundance ratio of H*₃/D*₃ for equivalent 6 keV beam fluxes increases sharply when the time span between neutralization and reionization is increased. The measurements show that a state of D*₃ with low rotational quantum numbers (N>0) is decaying on the time scale of the beam transit with a lifetime of about 0.2 μs. Results are interpreted in reference to the predissociation behavior of the 2p ²A″₂ electronic state of the radical. The disproportionate ratio of IH _*3/I_D*3 ≫ 1 is a consequenceof the relative abundances of precursor levels in H₃⁺ and D ₃⁺ that can transform into metastables by electron transfer.