Theoretical and experimental investigation on the stability of Cn=1-6H− and Cn=1-4Hx+ clusters

A theoretical study on the molecular structure of CnH− clusters, where 1 ⩽ n ⩽ 6, and CnHx+ clusters, where 1 ⩽ n ⩽ 4 and 0 ⩽ x ⩽ 2n + 2, has been performed at the DFT level. More than 300 configurations were examined and their total electronic energies ordered for each cluster mass. The D-plot methodology was employed for classifying different structures into cluster families and identifying the most stable structures. For each family, the binding energies of the analyzed cluster species have been determined and displayed as a function of the cluster mass. The fluctuations of these curves are then compared to experimental data, namely, to the dependence of relative ion desorption yields on cluster mass, obtained from Plasma Desorption Mass Spectroscopy (PDMS) of quite distinct types of organic samples: solid methane, cholesterol and pump oil vapor adsorbed on polycrystalline LiF. It is found that theoretical predictions and experimental data are in good agreement, showing that the abundance of the emitted small cluster ions is determined by their own structure and not by the structure of the original sample.

Highlights► A theoretical and experimental study of ionic hydrocarbon clusters was performed. ► More than 300 structures were examined and the results compared with mass spectra. ► Theoretical predictions and experimental data are in good agreement. ► The original sample does not influence the cluster abundance. ► Careful systematic search is important to reach the global minimum of clusters.