Experimental verification of quasibound predissociative states of H3+above the H++ H2dissociation limit

The presence of quasibound predissociative states of H 3 + above the dissociation limit has been detected, together with the vibrationally cooled, electronic ground state of this H 3 + beam. Evidence of these predissociative states was inferred by observing the H + fragment, resulting from the H 3 + photodissociation process, upon the excitation of the quasibound states with 1064 nm laser radiation. The centre-of-mass kinetic energy distributions of the fragment protons suggest that these originate, by predissociation after photon absorption, from H 3 + levels lying up to 1 eV below the dissociation limit, into levels lying above the lowest dissociation limit. The detection of protons with an energy release of less than the photon energy suggests that possibly all of the initial levels lie as far as 1.165 eV below the relevant dissociation limit, which may be the lowest dissociation limit. The acceleration energy of the H 3 + beam ranged between 6 and 10 keV.