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Threshold ion-pair production spectroscopy of HCl/DCl: Born-Oppenheimer breakdown in HCl and HCl+ and dynamics of photoion-pair formation

TitleThreshold ion-pair production spectroscopy of HCl/DCl: Born-Oppenheimer breakdown in HCl and HCl+ and dynamics of photoion-pair formation
Publication TypeJournal Article
Year of Publication2003
AuthorsHu, QJ, Melville, TC, Hepburn, JW
JournalJournal of Chemical Physics
Volume119
Pagination8938-8945
Date PublishedNov
Type of ArticleArticle
ISBN Number0021-9606
KeywordsBAND SYSTEM, DCL, DEPENDENCE, DF, DISSOCIATION-ENERGY, HF, IONIZATION, MOLECULE, STATES, TIPPS
Abstract

Threshold ion-pair production spectroscopy (TIPPS) has been applied to two isotopomers, HCl and DCl. From the high-resolution TIPP spectra the ion-pair thresholds of the two molecules have been precisely measured. Combined with the known ionization energy of H(D) and the electron affinity of Cl, the difference between their bond dissociation energies is calculated, and therefore an experimental determination of the effect of Born-Oppenheimer breakdown on the dissociation limit of the ground state potential curve has been obtained. The difference in D-e for the two isotopomers was found to be: D-e(H-Cl)-D-e(D-Cl)=3.2+/-1.0 cm(-1). The bond energy for HCl was in agreement with our previous determination, D-0(H-Cl)=35748.2+/-0.8 cm(-1). These results are compared to a recent study of Born-Oppenheimer breakdown in HCl by Coxon and Hajigeorgiou, where high resolution spectroscopic data was used to fit Born-Oppenheimer breakdown correction terms for the intramolecular potential function. The present study also measured the high resolution spectra for photoion-pair production for HCl and DCl in the threshold region for ion-pair production (similar to86 nm). Although there is qualitative agreement between the current results and previous experimental and theoretical work, there are some important differences. The possible mechanism for ion-pair formation in HCl and DCl is discussed in light of these high resolution results. (C) 2003 American Institute of Physics.

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