Ionisation and fragmentation of polycyclic aromatic hydrocarbons by femtosecond laser pulses at wavelengths resonant with cation transitions

When femtosecond laser pulses irradiate hydrocarbon molecules, then many fragmentation channels evident in nanosecond irradiation are bypassed, providing a strong analytically useful parent ion. However a number of molecules show only a very small or indeed no parent ions and recent papers suggest that those that do not produce parent peaks have cation transitions in resonance with the femtosecond laser wavelength. This Letter shows that this resonance effect is not universal and some aromatic molecules not only show strong parent peaks but also doubly and triply ionised entities when their cation absorption spectrum is strongly resonant at either the 800 or 400 nm or indeed both.