Structures of products from positive ion-molecule reactions by means of vibrational spectroscopy

Examples of various approaches to determining gaseous ion structures are described. Two cases are presented in which infrared multiple photon dissociation (IRMPD) spectroscopy provides characteristic information. Comparison with DFT-calculated normal modes differentiates isomers. The IRMPD spectrum of the even-electron C8D8F+ product ion from the ion-molecule reaction of CF3+ with perdeuterated acetophenone exhibits a degree of resolution sufficient to identify C6D5CFCD3+ and rule out ring-fluorinated isomers. The dimerization of phenylacetylene with its molecular ion has been explored, with the conclusion that a mixture of product ions is formed. The best match to the experimental spectrum is achieved by superimposing the bands calculated for ionized 1-phenylazulene and ionized 1,2-diphenylcyclobutadiene.