IR–microwave double resonance studies of dipole moments in the ν1 and ν3 states of ammonia

Infrared laser–microwave double resonance spectroscopy is used to observe the Stark effect of tunneling transitions within the ν1 and ν3 hydrogen stretching states of NH3. Dipole moments for 11 J,K states of ν1 and 3 J,K states of ν3 are measured to high accuracy. These data, combined with previous measurements in the ground and excited bending states, give a dipole moment function (in Debye) of: μv1v2v3v4=1.5610+7.2×10−3(v1+1/2)−2.271×10−1(v2+1/2)+3.75×10−2(v3+1)−1.65×10−2(v4+1). μe=1.561 D is the first experimental measurement of the NH3 equilibrium moment. These results are also used to analyze and recalculate the dipole moment measured by Shimizu and co-workers in a vNH=5 excited state of NH3.