INFRARED PHOTODISSOCIATION SPECTRA OF ACRYLONITRILE CLUSTER IONS

A coaxial infrared laser-ion beam photoabsorption spectrometer was con structed for the measurement of the vibrational spectrum of an acrylon itrile cluster cation, (CH2CHCN)(n)(+) (n = 3-10), by detecting photod issociation products of the cluster ion in the wavenumber range of 925 -1090 cm(-1). All the spectra measured in this n-range have an intense peak at 970 cm(-1), which is associated with a C=C-H out-of-plane vib ration of an acrylonitrile molecule in the cluster ion. The comparison of the spectra with an ab initio calculation shows that the cluster i on consists of a dimer ion core solvated with neutral acrylonitrile mo lecules. On the other hand, the acrylonitrile cluster anions did not e xhibit any optical absorption in the wavenumber range studied. This fi nding is consistent with our previous result that intracluster polymer ization takes place when an electron is attached onto a neutral cluste r of acrylonitrile.