Reexamination of the C2H3+ microwave and infrared spectra

► Hydrogen migration tunneling splittings in C-H stretch of C2H3+ are reanalyzed. ► Experimental barrier found: ∼1500 cm−1 agrees with ab initio literature: ∼1350 cm−1. ► Experimental A, B, C and tunneling offset angle θ agree with ab initio structures. ► Least-squares rms ∼50 times measurement error, due to dark-state perturbations.