Identification of the fragment (m/z = 181). (a) The fragmentation pattern of [py + 7H]⁺ extracted from MD trajectories. The color scheme for atoms is the same as the scheme in Fig. 1. The hydrogen diffusion is indicated by black arrows and the process of ethylene formation is indicated by red arrows. The computed IR spectrum of (b) the MD-determined isomer, (c) the EA-determined isomer, (d) the EA-determined isomer, and (e) the EA-determined isomer with their structure snapshots and relative energies, (f) The experimental IR spectrum of the fragment (m/z = 181). Vertical dashed lines have been drawn to aid the comparison between theory and experiment.