INFRARED PHOTOFRAGMENTATION SPECTRA OF C2H4-CENTER-DOT(NO)(N)(+) CLUSTER IONS

A line-tuneable CO2 laser has been used to excite one or more vibratio nal modes in ethylene molecules resident on sizeselected C2H4(NO)(n)() cluster ions, for n in the range 2-20. Excitation is followed by the observation of three separate fragmentation channels: -C2H4, -NO and -2NO, whose relative intensities are found to be extremely sensitive t o cluster size. The most marked transitions in fragmentation pattern a re found to occur between odd- and even-sized cluster ions, with decay channels favouring the formation of even electron ions. A summation o f fragment ion intensities as a function of laser wavelength is used t o determine infrared absorption profiles. Those profiles associated wi th several of the even-sized ions show evidence of two prominent absor ption features, one of which is attributed to the nu(7) infrared activ e vibrational mode in ethylene. A second absorption feature is tentati vely assigned as the nu(8) mode which, under normal circumstances, is Raman active; however, a mechanism is proposed whereby the ethylene mo lecule could become distorted.