A supersonic molecular beam mass spectrometer study of autoassociation in acetonitrile and propionitrile

Abstract

The autoassociation of gas phase dipole-dipole clusters of acetonitrile and propionitrile were studied. A supersonic molecular beam was used as a sampling system for the gas phase (10–100 torr) equilibrium of monomer and clusters of each nitrile system followed by mass spectral detection. Either monochromatic VUV light produced by an electron storage ring or electrons produced by a rhenium filament was used for ionization. Ions corresponding to the series (RCN) n H + were attributed to fragmentation of the unique neutral clusters present in the molecular beam. The temperature dependence of the cluster ions was used to determine the enthalpies of formation for the nitrile clusters. Both dimer and trimer clusters were found in gas phase acetonitrile with enthalpies of formation of −8.9 and −9.0 kcal mol −1, respectively. No clusters larger than dimer were found for propionitrile. The enthalpy of propionitrile dimer formation was −9.5 kcal mol −1.