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 r(e) values of 1.0367 and 1.0363 Angstrom, respectively. The small difference serves as a valuable internal consistency check and suggests that r(e) in NH4 lies in the range 1.0365 +/-0.0005 Angstrom. (C) 2001 American Institute of Physics.