Secondary ion mass spectrometry studies of molecular solids: the mechanism of cluster formation for frozen samples of water, benzene and cyclohexane

The secondary ion mass spectra (SIMS) of frozen samples of water, benzene, and cyclohexane are reported. A UHV spectrometer system designed for SIMS studies is described in detail. Ion clusters in the water spectra are particularly interesting in that clusters containing as many as 154 atoms, e.g. H(H[lowered 2]O[raised +])[lowered 51], which have lifetimes greater than tenths of milliseconds, have been detected. The SIMS spectra of the organic samples show fragmentation patterns similar to conventional electron impact mass spectrometry, however, clusters containing as many as 30 carbon atoms could be detected. A clustering mechanism which is qualitatively consistent with all of the experimental evidence is proposed. SIMS has also been used to detect the reactions Induced by active ion bombardment (AIB) of N2[raised +, lowered 2] on the frozen samples. The SIMS spectra exhibit ions containing reacted species only as a result of AIB and not by physisorption.