EXPERIMENTAL CHARACTERIZATION OF THE He $+$ I$^{35}$Cl({\it E},{\it v}$^{\dag}$=11,12) AND He $+$ I$^{35}$Cl({\it $\beta$},{\it v}$^{\dag}$=0-2) INTERMOLECULAR POTENTIAL ENERGY SURFACES

Author Institution: Department of Chemistry, Washington University, One Brookings Drive, CB 1134, Saint Louis, MO 63130Two-photon excitation of the T-shaped and linear He$\cdots$I$^{35}$Cl({\it X} $^{1}\Sigma^{+}$,{\it v}$^{\prime \prime}$=0) complexes are used to access multiple intermolecular vibrational levels within the He $+$ I$^{35}$Cl({\it E}0$^{+}$ $^{3}$P$_2$,{\it v}$^{\dag}$=11,12) and He $+$ I$^{35}$Cl({\it $\beta$}1 $^{3}$P$_2$,{\it v}$^{\dag}$=0-2) ion-pair state intermolecular potentials. The excitation utilizes different metastable intermolecular levels within the He $+$ I$^{35}$Cl({\it B} $^{3}\Pi_{0+}$,{\it v}$^{\prime}$=2,3) and He $+$ I$^{35}$Cl({\it A} $^{3}\Pi_1$,{\it v}$^{\prime}$=15) potentials, and thus varying Franck-Condon windows, to access levels with varying amounts of vibrational excitation within the ion-pair state intermolecular potential. The He $+$ ICl({\it E},{\it v}$^{\dag}$=11,12) and He $+$ ICl({\it $\beta$},{\it v}$^{\dag}$=0-2) intermolecular potentials are found to be nearly identical with an overall minimum in the near T-shaped orientation and binding energies {\it D} $_0^{\dag}$ = 40 cm$^{-1}$. Intermolecular stretching and bending frequencies are measured to be 25 and 13 cm$^{-1}$, respectively. Since common intermolecular levels are accessed by transitions from both the T-shaped and linear He$\cdots$ICl({\it X},{\it v}$^{\prime \prime}$=0) ground state conformers, the relative binding energies of the conformers can be directly measured; the linear conformer is found to be 5.4(2) cm$^{-1}$ more strongly bound than the T-shaped conformer