Understanding dehydrogenation sequence in fluorene+ by multiphoton ionisation-excitation processes

The dehydrogenation sequence in fluorene+ up to a loss of 3 hydrogen (H) atoms, is explored using a kinetic energy (KE) correlated time of flight mass spectrometer (ToFMS). Four dehydrogenation reactions are identified for the internal energy ranging between 8.5 and 9.0 eV. A dichotomy is observed in fluorene+ in the H-loss channel processed within the studied internal energy. This is explained with the help of a hydrogen migration process leading to post-ionisation isomerization, which is explored using DFT calculations. Presence of two modes of molecular hydrogen (H2) loss is also noted in the dehydrogenation sequence, including observation of direct elimination of H2 from fluorene+.