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 Title: Spectroscopic Studies Of Small Polyatomic Molecules Near Ion-pair Dissociation Thresholds Author(s): Kreis, Carla Contributor(s): Merkt, Frédéric; Hollenstein, Urs Subject(s): Electronic structure, potential energy surfaces Abstract: At high vibrational quantum numbers, ion-pair states (A$^+$--B$^-$) behave like high Rydberg states. Their level structure can be approximately described by Rydberg's formula after replacing the Rydberg constant $R_{\infty}$ by the appropriate mass-scaled value $R_{IP}=R_{\infty} \frac{\mu_{A^+-B^-}}{m_e}$.\footnote{E. Reinhold and W. Ubachs, Mol. Phys., 103:10, 1329-1352, (2005)} We present the results of spectroscopic investigations of high-lying excited ion-pair states of small polyatomic molecules in the vicinity of ion-pair dissociation thresholds. Such states have been extensively characterized in diatomic molecules (see ref. $^a$$^,$\footnote{S. Mollet, F. Merkt, Phys. Rev. A., 82, 032510, (2010)} and references therein) and are at the heart of the technique of threshold ion-pair production spectroscopy.\footnote{J.D.D. Martin, J.W. Hepburn. Phys. Rev. Lett., 79, 3154, (1997)} Only few studies have been carried out on polyatomic molecules.\footnote{R. C. Shiell, X. K. Hu, Q. J. Hu, J. W. Hepburn, J. Phys. Chem., 104, 19 (2000)}$^,$\footnote{Q. J. Hu, Q. Zhang, J.W. Hepburn. J. Chem. Phys., 123, 074310, (2006)} Polyatomic molecules exhibit denser series of ion-pair dissociation thresholds corresponding to the different rovibrational levels of the positively and negatively charged fragments. We will present the results of our investigations of OCS and H$_2$S in the vicinity of their lowest ion-pair dissociation thresholds. The experiments are carried out using cold samples in skimmed supersonic expansions. The region of the lowest ion-pair dissociation threshold is reached by single-photon excitation from the neutral ground state using narrow-band VUV radiation. The experiments provide access to the ion-pair dissociation energies from which the level structure of the ionic fragments can be determined as well as other thermochemical data such as electron affinities, ionization and dissociation energies. Issue Date: 2021-06-24 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111486 Date Available in IDEALS: 2021-09-24
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