Pure rotational spectroscopy of potassium chloride, KCl, up to 930 GHz and isotopically invariant analysis of KCl and NaClq

The pure rotational spectra of five isotopomers of KCl, i.e. 39K35Cl, 39K37Cl, 41K35Cl, 41K37Cl and 40K35Cl have been recorded with the Cologne terahertz high-resolution spectrometer. A total of 295 new rotational lines have been measured in the frequency region between 170 and 930 GHz. For the isotopomers 39K35Cl and 39K37Cl 107 and 82, respectively, rotational transitions were assigned from the vibrational ground state up to the seventh excited vibrational ðn # 7Þ state while the highest J quantum number was 127 (129). 104 lines were measured for the less abundant isotopomers of 41K35Cl and 41K37Cl with J # 128; n # 6 and J # 131; n # 5; respectively. Two lines were assigned to 40K35Cl, which has an abundance of 0.01% relative to 39K35Cl. The newly measured lines were fitted together with the previously published microwave and millimeter wave transitions to obtain an improved set of molecular parameters for the studied isotopomers. Besides this analysis, the isotopically invariant Dunham parameters Uij with the Born–Oppenheimer corrections for U01 have been determined for the potassium as well as sodium chloride. The NaCl experimental data have been taken from our recent submm highresolution study, where both isotopomers of NaCl were measured. The improved isotopically invariant parameters allow precise frequency predictions for the six KCl and two NaCl isotopomers (39K35Cl, 39K37Cl, 41K35Cl, 41K37Cl, 40K35Cl, 40K37Cl, 23Na35Cl and 23Na37Cl) to be made far into the terahertz region. q 2004 Elsevier B.V. All rights reserved.