Infrared Vibrational Pre-dissociation Spectroscopy of $Na^{+}(CH_{3}OH)_{m}((CH_{3})_{2}CO)_{n} m=1-3, n=3-8$

Author Institution: School of Chemical Sciences, 505 S Mathews Ave., Urbana, IL 61801; Pennsylvania State University, University Park, PA 16802Clusters of $Na^{+}(CH_{3}OH)_{m}((CH_{3})_{2}CO)_{n} m=1-3, n=3-8$ were produced in a molecular beam by co-expanding methanol and acetone in argtone to produce a distribution of mixed neutral clusters, which were then impacted with $Na^{+}$ from a thermal source. The species of interest were mass selected using a series of quadrupole mass filters. The carbonoxygen stretch of the methanolsin the mass selected ion clusters were excited using the $9.6 \mu m$ spectral region of a line tunable $CO_{2}$ laser. The increase of the internal energy of the ion cluster associated with the absorption of an infrared photon significantly increases the unimolecular dissociation rate of the ion clusters. The clusters which undergo predissociation on the time scale of the experiment are ejected from the quadrupole mass filter and a loss of signal intensity due to vibrational excitation is used to determine vibrational dissociation cross sections. The vibrational pre-dissociation spectra of $Na^{+} (Methanol)_{m}(Acetone)_{n}$ show single peaks for clusters containing single methanols. Clusters containing more than one methanol show an absorption at the same locations as the single methanol species with four or more acetones, except a new peak is observed red-shifted by about $10 cm^{-1}$. The structural implications will be discussed with the aid of Monte Carlo calculations