IR DOUBLE-RESONANCE EXPERIMENTS WITH SIZE-SELECTED CLUSTERS FOR IDENTIFICATION OF ISOMERS

Infrared photodissociation spectra of (CH3OH)(n) clusters (n=2, 3 and 6) and the mixed dimer C2H4.CH3COCH3 are presented. The clusters are g enerated in a supersonic jet expansion and size selected by scattering from a helium atomic beam combined with mass spectrometric detection. Continuous CO2-lasers are used to vibrationally excite the molecules in the cluster leading to rapid dissociation of the complex. Various d issociation peaks that are found in single-laser dissociation spectra can be assigned unambigously in a pump-probe experiment with two laser s to either different isomers (acetone-ethene dimer) or splitted lines of one isomer (methanol hexamer). For size distributions, the method is able to select contributions of single masses which is demonstrated for mixtures of methanol dimers and trimers.