Millimeter-Wave Rotational Stark Spectra of HNCO, DNCO, and HN3: Dipole-Moment Changes with K

Abstract

By employing a parallel‐plate semifree‐space cell the millimeter‐wave rotational Stark spectra of HNCO, DNCO, and HN₃ have been observed in the ground vibrational state. Analysis of the Stark effect for the J=3→4 transitions yields the dipole‐moment component along the axis of smallest moment of inertia. For these very slightly asymmetric rotors the dipole moment is observed to decrease with increasing K. For HNCO (J=3→4), the dipole moments are found to be (Debye units) $$\begin{array}{c}{\text{K=0,\hspace{0.17em}μ}}_a{\text{=1.613±0.002,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}K=2,\hspace{0.17em}μ}}_a\text{=1.540±0.001,}\\ {\text{K=1,\hspace{0.17em}μ}}_a{\text{=1.575±0.002,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}K=3,\hspace{0.17em}μ}}_a\text{=1.500±0.002;}\end{array}$$ for DNCO (J=3→4), $${\text{K=1,\hspace{0.17em}μ}}_a{\text{=1.602±0.003,\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}K=2,\hspace{0.17em}μ}}_a\text{=1.580±0.001;}$$ and for HN₃ (J=3→4), $${\text{K=1,\hspace{0.17em}μ}}_a{\text{=0.8369±0.0020,\hspace{0.17em}\hspace{0.17em}K=2,\hspace{0.17em}μ}}_a\text{=0.8247±0.0002.}$$ The results are discussed in terms of the electronic structures of the molecules.