Observation of the isomer effect on charge transfer from C3H4 molecules (allene and propyne) at keV energies

Two-body dissociation of C3H4 isomers investigated by 50 keV/u Ne8+ impact

The fragmentation of two isomers of C₃H₄, propyne (CH₃CCH) and allene (CH₂CCH₂), is investigated by 50 keV/u Ne⁸⁺ impact. Obvious isomer effects are observed by comparing the time-of-flight spectra generated from the two isomers. Six two-body fragmentation channels of C₃H₄ ²⁺ dications are identified for each isomer. CH₂ ⁺ + C₂H₂ ⁺ is found to be the most favored CC bond breaking channel for both isomers, indicating that CH₃CCH²⁺ intends to rearrange to the structure containing the CH₂ group before fragmentation. For CH bond breaking channels, it is found that the CH₃CCH which contains a CH₃ group is more efficient for H₂ ⁺ and H₃ ⁺ ejection. In addition, two-body dissociation channels of C₃H₄ ³⁺ trications are identified. While the H⁺ + C₃H₃ ²⁺ channel is observed in the fragmentation of both isomers, the H₂ ⁺ + C₃H₂ ²⁺ channel only occurs in the fragmentation of CH₃CCH³⁺. For CH₂CCH₂ ³⁺, the peak and shoulder structures in the kinetic energy release spectrum of the H⁺ + C₃H₃ ²⁺ channel are attributed to different geometries of the C₃H₃ ²⁺ product.