Ion-molecule reactions of organic molecules with noble metal atoms in superfluid helium droplets

Superfluid helium droplets (HeDs) provide a unique environment for the study of physical and chemical phenomena at a very low temperature. Properties of HeDs include the very low temperature (0.37 K), superfluidity and the ability to capture a wide variety of atoms and molecules. Subsequently, the molecules isolated in HeDs can be studied by mass spectrometry and/or spectroscopy. In this work, dissociative ion-molecule reactions of metal-organic complexes formed in superfluid HeDs are reported. Two organic molecules, 1-pentanol and 1,9-decadiene, and two noble metals, gold (Au) and silver (Ag), were employed to form binary metal-organic complexes by sequential addition of organic molecules and metal atoms to superfluid HeDs. The resulting complexes were then investigated by mass spectrometry. Electron impact of a doped HeDs first creates a He+ ion, which ionizes the embedded molecules through resonance charge transfer. This highly energetic process delivers excess energy to the molecular clusters, leading to dissociative ion-molecule reactions. The mass spectra show softening effects and caging effects induced by the superfluid helium for both 1-pentanol and 1,9-decadiene, and the co-addition of Ag or Au has been found to have minor influence to the fragmentation patterns, except for the 1,9-decadiene-Au complex. This is attributed to the different ionization energy of the selected molecules and metals, which influences the overall energy delivered to the organic molecules studied and thus the degree of fragmentation.