INFRARED PHOTODISSOCIATION OF SIZE-SELECTED ACETONITRILE CLUSTERS

Photodissociation spectra of (CH3CN)n clusters from n=2 to n=5 have been measured near the monomer frequencies of the ν4 mode at 1020.3 cm-1 (CC stretch) and the ν7 mode at 1041.8 cm-1 (CH3 rock) using a line tunable cw CO2 laser. The clusters are size selected by a scattering process with He atoms and a quadrupole mass spectrometer. The results for the ν4 mode show one peak shifted 2 cm-1 to the red with decreasing width when going from n=3 to n=5. For the ν7 mode a blue-shift of 4 cm-1 is observed. For the pentamer an additional peak shifted 10 cm-1 to the red is seen which, together with the narrow linewidth of the ν4-mode spectrum, indicates a structural change. © 1990.