The structure of NH3⋅H2S and free internal rotation effects

Abstract

The structure of NH3⋅H2S has been determined from microwave and radiofrequency spectroscopy of this complex and its deuterated isotopomers, using molecular beam electric resonance techniques. Rotational constants, electric dipole moments and nitrogen quadrupole coupling constants were obtained from the spectra. The molecule was found to have a linear, hydrogen bonded structure with the ammonia as the proton acceptor. The N⋅⋅⋅S distance is 3.639 Å, the root-mean-square angular deviation of the NH3 axis from the N–S axis is 24.6° and the H2S C2 axis is 40.5° from the N–S axis. Although the molecule is an asymmetric rotor, first-order Stark effects were observed for K=1 rotational levels. These Stark effects are caused by torsional oscillations which are essentially ammonia monomer free internal rotation. Similar effects were observed for NH3⋅H2O and are reported here.