Hyperfine structure of the J=1 ← 0 transition of H35Cl and H37Cl:: improved ground state parameters

The pure rotational J = 1 <-- 0 transitions of (HCl)-Cl-35 and (HCl)-Cl-37 have been observed in the millimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to Cl-35 or Cl-37 and H. The present observations allow to provide not only very accurate hyperfine constants but also, joint together with previous data, the most accurate ground state rotational parameters known up to now. The experimental determination of the hyperfine parameters has also been supported by ab initio computations. (C) 2004 Published by Elsevier Inc.