Determination of bond dissociation energies by threshold ion-pair production spectroscopy:: An improved D0(HCl)

A recently developed form of threshold ionization spectroscopy has been used to determine the bond energy for HCl to spectroscopic accuracy (+/-0.8 cm(-1)). This method is based on excitation to highly vibrationally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were selectively detected using electric-field induced dissociation. By systematically varying the electric fields involved, and scanning the exciting photon energy, it was possible to determine the field-free energetic threshold for (HCl)-Cl-35 + h v--> H+ + Cl-35(-). Using this energy, together with the known values of the ionization potential of H and electron 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)02443-X].