Comparison of methyl and hydroxyl protons generated in a Coulomb explosion event: application of a time-of-flight gating technique to methanol clusters

A time-of-flight (TOF) mass spectrometry gating technique is applied to a study of methanol clusters subjected to ionizations via intense femtosecond laser pulses. The resulting high charged species (C2+, C3+/O4+) acquire large amounts of kinetic energy resulting from Coulomb repulsion of multicharged atomic ions that reside in close proximity to one another. Protons which are of two kinds, methyl and hydroxyl, also acquire large amounts of kinetic energy. When compared with protons generated from the Coulomb explosion of water clusters ((H2O)n, n≤20), protons from methanol clusters ((CH3OH)n, n≤10) acquire less overall average kinetic energy, which is in agreement with earlier findings that suggest greater clustering yields higher energy. Interestingly, despite the lower average kinetic energy released, the methanol protons peak at a higher value of energy than those generated in the water cluster system, an effect attributed to the presence of both methyl and hydroxyl groups.