Centrifugal Distortion in Asymmetric Top Molecules. III.H2O,D2O, and HDO

Abstract

Structural and potential constants obtained from infrared data are used with the theory of vibration-rotation interaction to obtain rotational and distortion parameters for the molecules ${\mathrm{H}}_2$O, ${\mathrm{D}}_2$O, and HDO; transition frequencies calculated using these parameters are compared with those observed in the microwave region, and, in the case of HDO $Q$-branch lines, a simple relation between the two sets is obtained. The validity of approximation theories as applied to HDO $Q$-branch transitions is discussed. Methods of analyzing the observed spectrum of HDO are described, and so-called "observed" parameters for this molecule are obtained; the rotational constants are found to be $a=7.0396\mathrm{}\pm 0.0005\times {10}^5$ Mc/sec, $b=2.7360\mathrm{}\pm 0.0005\times {10}^5$ Mc/sec, $c=1.9186\mathrm{}\pm 0.0005\times {10}^5$ Mc/sec, $\kappa =-0.6841\mathrm{}\pm 0.0002$.