DETERMINATION OF BOND-DISSOCIATION ENERGIES BY THRESHOLD ION-PAIR PRODUCTION SPECTROSCOPY - AN IMPROVED D-0(HCL)

A recently developed form of threshold ionization spectroscopy has bee n used to determine the bond energy for HCl to spectroscopic accuracy (+/-0.8 cm(-1)). This method is based on excitation to highly vibratio nally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were select ively detected using electric-field induced dissociation. By systemati cally varying the electric fields involved, and scanning the exciting photon energy, it was possible to determine the field-free energetic t hreshold for (HCl)-Cl-35 + h v--> H+ + Cl-35(-). Using this energy, to gether with the known values of the ionization potential of H and elec tron affinity of Cl, a new estimate for the dissociation energy of HCl was obtained: D-0((HCl)-Cl-35)=35 748.2+/-0.8 cm(-1) [S0021-9606(98)0 2443-X].