Collision‐induced dissociation of the lower alcohols. A thermochemical study

Collision‐induced dissociation of the molecular ions and of some of the fragment ions foremed on ionization of methanol, ethanol and n‐propnol have been studied at high energy resolution in a mass spectrometer. The translational energy lost upon collision and the kinetic energy releasedupon fragmentation of the collisionally excited species have been measured by the methods of ion kinetic energy spectromety. The results of the translational energy loss measurements compare well with excitation energies predicted for each reaction form breakdown curves showing the relative abundances of the ionsas a fuction of internal energy. This correspondence is evidebce that the ionic reactions following electron‐impact excitation and those following collisional excitation with neutral molecules at relative traslational energies in the range of several kilovolts are at least qualitatively independent of the method of excitation. The occurrence of the corresponding spontaneous fragmentations in the alcohols has also been studied and the kinetic energy releases accompanying these reactions have been determined. In a few cases, metastable peaks were observed which did not increase in intensity when collision gas added and this phenomenon is associated with particular features of the reaction thermochemistry. Reactions which generally occur to very small extents in mass spectromety, such as methylene elimination, have been observed in highly excited ions. The methods developed in this study allow the decription of the thermochemistry of the reaction of highly excited ions, indlcuding the experimental determination of the partitioning of the nonfixed energy of the activated complex. This procedure complemets and extends energy partitioning studies made on metastable ions in which the partitioning of the reverse activation energy is the more readily accessible.