## HIGH-RESOLUTION PFI-ZEKE PHOTOELECTRON SPECTROSCOPY OF Cl$_2$: THE GROUND (X$^+$ $^2\Pi_{\mathrm{g}}$) AND FIRST EXCITED (A$^+$ $^2\Pi_{\mathrm{u}}$) ELECTRONIC STATES OF Cl$_2^+$

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Ohio State University##### Abstract:

Recently, two studies have been devoted to the low-lying electronic states of Cl$_2^+$, one by PFI-ZEKE photoelectron (PE) spectroscopy of the $\mathrm{X}^+\leftarrow\mathrm{X}$ transition, \emph{J.\ Chem.\ Phys.} \textbf{127}, 104307 (2007).} and one by laser-induced-fluorescence spectroscopy of the $\mathrm{A}^+\rightarrow\mathrm{X}^+$ band system, \emph{66$^{th}$ Int.\ Symposium on Molecular Spectroscopy}, Book of Abstracts, p.\ 169 (2011).}. To complement the information available on the X$^+$ and A$^+$ electronic states of Cl$_2^+$, we have recorded partially rotationally resolved single-photon PFI-ZEKE PE spectra of the $\mathrm{X}^+\ ^2\Pi_{\mathrm{g},i}\leftarrow\mathrm{X}\ ^1\Sigma_\mathrm{g}^+$ and $\mathrm{A}^+\ ^2\Pi_{\mathrm{u},i}\leftarrow\mathrm{X}\ ^1\Sigma_\mathrm{g}^+$ ($i=3/2,\,1/2$) photoionizing transitions of Cl$_2$ in the wavenumber ranges $92\,500-96\,500\ \mathrm{cm}^{-1}$ and $106\,750-115\,500\ \mathrm{cm}^{-1}$. These regions correspond to transitions to low-lying vibrational levels of the X$^+$ state with $v^+=0-5$ and to transitions to vibrational levels of the X$^+$ state with $v^+=25-45$ and vibrational levels of the A$^+$ state with $v^+\leq 7$.\\ The analysis of the rotational structure and the isotopic shifts of these spectra has enabled the derivation of an improved value of the first adiabatic ionization energy ($92\,647.7\pm0.3\ \mathrm{cm}^{-1}$ for $^{35}$Cl$_2$). In combination with measurements of ion-pair states with $n\approx 1800$, \emph{Phys.\ Rev.\ A} \textbf{82}, 032510 (2010).}, new values for the dissociation energies $D_0$ of Cl$_2$ and Cl$_2^+$ could also be derived. The potential energy function of the X$^+$ state of Cl$_2^+$ was determined in a least-squares fitting procedure. Spin-orbit splittings were derived for many vibrational levels of the X$^+$ and A$^+$ states. Combining our results with other results$^{b,}$, \emph{Chem.\ Phys.} \textbf{83}, 203 (1984).}$^{,}$, \emph{J.\ Mol.\ Spect.} \textbf{230}, 72 (2005).}$^{,}$, \emph{Chem.\ Phys.} \textbf{89}, 313 (1984).}, several low-lying vibrational levels of the upper spin-orbit component of the A$^+$ state could be assigned for the first time. The PFI-ZEKE PE spectra also contain a series of as yet unassigned lines and reveal numerous perturbations.

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Author Institution: ETH Zurich, Laboratorium fur Physikalische Chemie, Wolfgang Pauli-Strasse 10, 8093 Zurich, Switzerland

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