Fig. 4: Theoretically calculated mechanism for the cis-to-trans-HNCO^•− isomerization.

A Potential energy profile of the negatively charged diabatic surface (blue curve, for HNCO^•−) and the neutral diabatic surface (orange curve, for neutral HNCO) along the bond inversion angle (∠NCO) at the XYGJ-OS/jul-cc-pVTZ level. Key structures are shown, including the transition states (TS1 and TS2). B Potential energy profiles along the gas-phase C-inversion (blue solid line) and the H-rotation (black solid line) instanton pathways. The dotted lines represent a downhill intrinsic reaction coordinate (IRC) calculation connecting the instanton endpoint to the trans minimum. In the unit of the (mass-weighted) tunneling path length, amu stands for atomic mass unit. The two deep tunneling instanton trajectories are shown. The numbers indicate the percentage contribution of each atom to the total squared mass-weighted tunneling path length for the respective gas-phase pathways. C Comparison of the potential energy profiles for the C-inversion instanton pathways in the gas phase (blue solid line) and within the QM/MM model (dashed magenta line). D A cross-sectional view of the C-inversion instanton pathway embedded in the QM/MM model simulating the neon matrix. The surrounding Ne atoms are partitioned into an inner shell (light blue) flexible in the instanton calculations and a fixed outer shell (dark blue). Atomic contributions to the tunneling path within the matrix are shown.