Precise Measurement of the Pure Rotational Submillimeter-Wave Spectrum of HCl and DCl in Their v = 0, 1 States.

High-resolution sub-Doppler Lamb-dip measurements were performed on the low-J pure rotational transitions of the hydrogen chloride isotopomers H35Cl, H37Cl, D35Cl, and D37Cl in the submillimeter-wave region up to 646 GHz. For the J = 1-0 transitions of the two HCl isotopomers, the hyperfine splitting due to the hydrogen nuclear spin-rotation interaction is resolved. Furthermore Doppler-limited lines of the DCl J = 3 <-- 2 transition around 965 GHz as well as hyperfine-resolved rotational transitions in the first excited vibrational state were recorded up to 1.22 THz. The new frequencies were analyzed in a global fit together with FIR data yielding a set of mass-invariant rotational parameters. Isotopically invariant hyperfine parameters were obtained also from the global fit. Inclusion of the precise results from molecular beam electric resonance measurements allowed the determination of higher orders of the vibrational and rotational expansion coefficients of the chlorine and hydrogen hyperfine interactions. The precise transition frequencies reported here should be useful as secondary calibration standards in the submillimeter-wave and terahertz region. Copyright 1998 Academic Press. Copyright 1998Academic Press