Structure and photodissociation spectra of mixed ethene–acetone clusters

Abstract

Infrared photodissociation spectra of the mixed complexes C2H4–CH3COCH3 and C2H4–(CH3COCH3)2 have been observed after size selecting them by scattering from a helium beam combined with mass spectrometric detection. The excitation of the ν7-out of plane symmetric wagging mode of ethene near its gas phase frequency at 949.3 cm−1 with a cw-CO2 laser leads to a characteristic depletion of the cluster beam. The dissociation spectrum of the 1:1 complex can be explained by two peaks at 950.8 and 961.6 cm−1. Calculations of minimum energy configurations and band shifts based on an empirical site–site potential show that these frequencies can be attributed to the absorption of two different isomers. They correspond to the two different binding patterns of the H atoms of ethene to the O atom of acetone and those of acetone to the C–C group of ethene, respectively. For the 1:2 complex, a large peak at 958.5 cm−1 and a smaller one around 940.5 cm−1 are found which can be explained in a similar manner by several isomers found in the structure calculations.