OBSERVATION OF THE ROTATIONAL SPECTRA OF (HEH-HE-4 (HED+)-HE-4, (HEH+)-HE-3, AND (HED+)-HE-3())

Low J rotational transitions of (HeH+)-He-4, (HeD+)-He-4, (HeH+)-He-3, and (HeD+)-He-3 were observed in the 2-5 THz region with a high-preci sion far-infrared spectrometer. Dunham coefficients Y-kl and isotopica lly independent parameters U-kl, Delta(kl)(He), and Delta(kl)(H) were determined. In particular, Delta parameters with k = 0 and l = 1.2 wer e determined with unprecedented accuracy, and provide important inform ation for breakdown of the Born-Oppenheimer approximation. The lowest J = 1 <-- 0 transition of (HeH+)-He-4 observed at 2010.1839(2) GHz wil l be an important future probe for detecting this species in space.