Ionization and fragmentation of isomeric van der Waals complexes embedded in helium nanodroplets.

The ionization and charge transfer processes, which occur when a doped helium droplet undergoes electron impact, are studied for droplets doped with van der Waals complexes with various structures and electrostatic moments. The mass spectra of the two isomers of hydrogen cyanide complexed with either cyanoacetylene or acetylene in helium droplets were obtained using optically selected mass spectrometry, and show that the structure of the complex has a large effect on the fragmentation pattern. The resulting fragmentation pattern is consistent with an ionization process in which charge steering strongly influences the site of initial ionization. The observed dissociation products may also be subject to caging by the helium matrix.