Mass spectrometric and photoionisation investigations of the structure of heterogeneous clusters

Abstract Heterogeneous clusters have been produced by a supersonic expansion of two compounds (COAr, N 2 Ar) and subsequently ionised by either electron impact or photoionisation. The mass spectra show clusters of the form Ar n − m X m + (X = CO, N 2 ) and, especially in the case of CO, are governed by fragmentation of precursor neutral clusters. The photoionisation spectra for small, mass-selected ionic clusters also show strong evidence of fragmentation of large neutral clusters. The behaviour of mixed COAr clusters is seen to be significantly different from that of N 2 Ar clusters and we postulate a model for the photoionisation of heterogeneous clusters which involves the existence of more than one energy threshold corresponding to the ionisation of each of the constituent species.