Threshold Ion-Pair Production Spectroscopy

Current Worker: Qichi Hu

Threshold Ion-Pair Production Spectroscopy (TIPPS) is a high resolution threshold photoionization technique, which monitors the process: AB(q) + hv → A⁺---B^-→ A⁺(q') + B^- (q''), where q and q', q'' represent the initial and final quantum states of the system. It involves the excitation of molecules from the ground state to the highly vibrationally excited A⁺--B^- ion-pair states. These weakly bound states are then detected by field dissociation using electric pulses.

There are a few advantages for this technique. First, since only threshold ions are detected in our high resolution TIPP spectra, we can measure the ion-pair dissociation energy and thus the bond dissociation energy with unprecedented accuracy (1 cm^-1 for diatomics and a few cm^-1 for polyatomics). Second, if one or both of the two ionic fragments have more than one atom, we will be able to measure the energetic levels of the ionic fragments. Third, we can obtain information about the mechanism of ion-pair dissociation processes.

TIPPS has been successfully employed to molecules (in time order) O₂, HCl, HF, H₂/D₂, H₂S, DCl, DF, HCN and (HF)₂. Results of all these molecules except the last two have been published.

Publications:

1. J. D. D. Martin and J. W. Hepburn, Phys. Rev. Lett. 79, 3154 (1997)
2. J. D. D. Martin and J. W. Hepburn, J. Chem. Phys. 109, 8139 (1998)
3. R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)
4. R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, Faraday Discuss. Chem. Soc., 115, 331(2000)
5. Q. J. Hu, T. C. Melville, and J. W. Hepburn, J. Chem. Phys. 119, 8938 (2003)
6. Q. J. Hu and J. W. Hepburn, J. Phys. Conf. Ser., in press (2004)