Electronic, structural, and hyperfine interaction investigations on Rydberg molecules: NH4, OH3, and FH2

The geometrical structures of NH4 and OH3 were optimized at the MP2 level w ith the aug-cc-pvdz, aug-cc-pvtz, and aug-cc-pvqz basis set plus s-type dif fuse functions. The adiabatic ionization potential, barrier height, and dis sociation energy of NH4 and OH3 were calculated with the above basis set se ries and were extrapolated to the infinite basis set limit. The theoretical ionization potential of NH4 was in very good agreement with the experiment al value. The N-H bond lengths of NH4 and NH4+ at the infinite basis set li mit were obtained by parabolic interpolation around the equilibrium point. FH2 was optimized at the UHF, B3LYP, and MP2 levels. However, only a dissoc iated ground state was found. The potential energy curves for dissociation of the above molecules were calculated with MP2. The relative stabilities o f these molecules and their isotopic counterparts are discussed. Theoretica l hyperfine calculations were performed in the gas phase as well as in a ne on matrix for NH4 and OH3 with a single-reference configuration interaction method (CI) and multireference single- and double-excitation methods (MRSD ), respectively. For FH2, only gas phase calculations are carried out. The contours of the singly occupied orbitals of NH4 and OH3 in the gas phase an d in the neon matrix are plotted to show their s-type character.