Profound isotope effect in dissociation of triatomic hydrogen.

Three-particle dissociation of high-lying Rydberg states of D3 is induced by an external electric field. We observe that the momentum vector correlation map of the center-of-mass motion of the fragments converges near the ionization threshold to two distinct fragment configurations, the near linear geometry and the symmetric acute angle geometry. A comparison is made with the momentum vector correlation map recorded in dissociative recombination of D3+ with slow electrons and with the corresponding results for H3 where the acute angle geometry is conspicuously absent.