The equilibrium structure of the ammonium radical Rydberg ground state

The equilibrium structure of the ammonium radical is determined by an extrapolation procedure of large [up to CCSD(T)/aug-cc-pV5Z] coupled cluster calculations and analysis of experimental rotational constants corrected for effects of rotation–vibration interaction. These approaches yield re values of 1.0367 and 1.0363 Å, respectively. The small difference serves as a valuable internal consistency check and suggests that re in NH4 lies in the range 1.0365±0.0005 Å.