title: Ion calorimetry: Using mass spectrometry to measure melting points.
abstract: Calorimetry measurements have been used to probe the melting of aluminum cluster cations with 63 to 83 atoms. Heat capacities were determined as a function of temperature (from 150 to 1050 K) for size-selected cluster ions using an approach based on multicollision-induced dissociation. The experimental method is described in detail and the assumptions are critically evaluated. Most of the aluminum clusters in the size range examined here show a distinct peak in their heat capacities that is attributed to a melting transition (the peak is due to the latent heat). The melting temperatures are below the bulk melting point and show enormous fluctuations as a function of cluster size. Some clusters (for example, n = 64, 68, and 69) do not show peaks in their heat capacities. This behavior is probably due to the clusters having a disordered solid-like phase, so that melting occurs without a latent heat.
authors.affiliation: Chemistry Department, Indiana University, Bloomington, Indiana 47405, USA.
authors.forename: Colleen M
authors.initials: CM
authors.lastname: Neal
authors.forename: Anne K
authors.initials: AK
authors.lastname: Starace
authors.forename: Martin F
authors.initials: MF
authors.lastname: Jarrold