Matching of Zeeman and tunneling levels in the proton spin rotating frame is used to detect splitting of the torsional ground state due to rotational tunneling of the NH4 group in solid NH4I. When highly polarized Zeeman splitting matches tunneling splitting a fast resonant transfer of polarization between Zeeman and tunneling states occurs. This in rum causes a change of the proton magnetization. When the magnetization change is monitored as a function of the magnetic field strength in the rotating frame, peaks are observed whenever two levels match. The model spectrum of the NH4 group with a split F-symmetry state, indicating that the symmetry of the lattice potential at the site of the NH4 group is lower than tetrahedral, reproduces the observed spectrum. The energy differences between the A state and the nondegenerate, lower F state and between this F state and the degenerate, higher F state, as measured by level matching in units kHz, are 82 +/- 4 and 41 +/- 2, respectively. The magnetization evolution spectrum shows peaks at 78 +/- 3 and 116 +/- 4 kHz which equal the anticipated A to lower F and the lower F to higher F energy differences.