Riya Gupta, Devendra Mani
We have studied the electron ionization-induced fragmentation dynamics of acetonitrile clusters isolated in superfluid helium nanodroplets. The obtained mass spectra reveal a rich fragmentation pattern, including a series of the most prominent (CH3CN)k-1H+ fragments, along with a series of weaker signals arising from ( CH 3 CN ) k •+ , (CH3CN)k-1CH2CN+, mono 13C isotopologues of (CH3CN)k-1H+, HenCH3 +, and HenCH2 •+ fragments. Additionally, in the mass range 10-82 u, peaks corresponding to (CH3CN)CHx + (x = 0-3), (CH3CN)CN+, and ( CH 3 CN ) CHCN •+ fragments were observed. Compared with molecular beam experiments, fragments in the mass range 42-82 u indicate the presence of additional direct fragmentation channels in helium droplet experiments. To determine the origin of the observed fragments, their intensity variation with acetonitrile partial pressure was analyzed. The assignments were further validated using CD3CN isotopologues. The (CH3CN)k-1H+ and (CH3CN)k-1CH2CN+ fragments both originate from the (CH3CN)k clusters of the same size. Moreover, for the clusters with k > 2, the ( CH 3 CN ) k •+ fragments also share the origin with (CH3CN)k-1H+ and (CH3CN)k-1CH2CN+ fragments. These findings provide detailed, crucial insights into the chemistry of acetonitrile clusters, initiated by ~24.6 eV of He•+ ions, at ultralow temperatures.