Microwave Spectrum and Rotational Constants for the Ground State of D2O

The rotational levels of the ground vibrational state of D₂O have been studied utilizing 29 observed microwave transitions and 259 rotational energy differences obtained from infrared measurements. Seventeen of the microwave lines in the region 70–310 GHz have been observed in the course of this work. Eighteen linearly independent rotational constants are required to fit the observations: three constants of the second power of the angular momentum, five constants of the fourth power, seven constants of the sixth power, and the coefficients of the operators $P_z^8{\mathrm{,\; P}}_z^6{P}^2{\mathrm{,\; P}}_z^{10}$ . Values of these constants and the calculated microwave transition frequencies up to 1000 GHz are reported. The coefficients of $P_z^2{\mathrm{,\; P}}_x^2{\mathrm{,\; P}}_y^2$ are, respectively, $\text{A\hspace{0.17em}=\hspace{0.17em}462 292.37\hspace{0.17em}±\hspace{0.17em}0.43, B\hspace{0.17em}=\hspace{0.17em}217 979.95\hspace{0.17em}±\hspace{0.17em}0.27}$ , and $\text{C\hspace{0.17em}=\hspace{0.17em}145 303.34\hspace{0.17em}±\hspace{0.17em}0.14}\mathrm{MHz}$ .