that are intermediate between those of argon and water.45
ConclusionWe have presented in this paper the first detailed study of molecular solvation in neutral clusters. Using mass spectrometric detection in association with laser-induced photofragmentation, it has been possible to determine infrared absorption profiles for the following cluster systems: (CH,OH),, (CH3CH20H),, CH30H.(H20),, CH3CH20H.(H20),, SF,*(D20),, and SF,. (H20),. In pure methanol clusters, the measured profiles display features that are consistent with the methanol moving toward bulk behavior as the cluster size increases. In small methanol clusters, the results suggest that hydrogen bonding between molecules is dominated by proton donor rather than proton acceptor bonds. Confirmation of this bonding arrangement is found in the spectra recorded from the mixed methanol/water clusters. To account for the observed peak width and red shift in these clusters, we propose that individual methanol molecules predominantly form proton acceptor bonds with the water. The lack of a significant spectral shift from either pure ethanol clusters or mixed ethanol/water clusters prevents us from drawing any firm conclusions regarding their behavior. However, the evidence does suggest that any spectral shift present is due to hydrogen bonding rather than steric interactions. The recorded spectra from mixed SF,/water clusters suggest that the SF, sits on or close to the surface of the cluster.
Acknowledgment.We thank the SERC for the award of a research studentship to J.C., for an Advanced Research Fellowship to B.J.W. and for an equipment grant. We also thank A. AlMubarek for assistance with some of the experiments.Anion exchange in anodically synthesized free-standing membranes of polypyrrole tosylate was studied by a combination of spectrophotometry, ac impedance, potentiometry, and electrochemical techniques. The short-time diffusion profiles could be analyzed in terms of a semiinfinite planar diffusion model. The apparent diffusion coefficients extracted via application of this model span the 10-12-10-10 cm2/s range. These values are compared with the results of recent measurements in other laboratories on other polymer systems, including polyacetylene. The diffusion coefficient for chloride exchange was also measured by the low-frequency ac impedance technique; the value thus obtained was in good agreement with that culled from spectrophotometric analyses. The diffusion was strictly charge-compensating as gleaned from chemical analyses of the exchanged polypyrrole membranes in chloride and phosphate bathing media. Polypyrrole morphology and bathing medium pH were used as two other variables to study the anion-exchange process. Finally, the ac resistance of the polypyrrole membranes was monitored prior to and after anion exchange. Contrary to the findings of previous authors, only modest changes in the membrane conductivity were noted as a function of anion composition.