		10min:

OBSERVATION OF THE ROTATIONAL SPECTRA OF ⁴HeH⁺, ⁴HeD⁺, ³H eH⁺, and ³HeD⁺.

KOJIRO TAKAGI, FUSAKAZU MATSUSHIMA, Department of Physics, Toyama University, Toyama 930, Japan; TAKESHI OKA, Department of Chemistry, Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637.

Low J rotational transitions of ⁴HeH⁺, ⁴HeD⁺, ³HeH⁺, and ³ HeD⁺ have been observed in the 2-5 THz frequency region with a high-precision far-infrared spectrometer using a tunable radiation source. Observed frequencies have been incorporated with previous infrared measurements to determine Dunham coefficients Y_kl and isotopically independent parameters U_kl, Delta _kl^ He, and Delta _kl^ H. In particular, constants with k=0 and l=1 and 2 have been determined with unprecedented accuracy and will provide important information for breakdown of the Born-Oppenheimer approximation. The lowest J=1<-0 transition of ⁴HeH⁺ observed at 2010.1839(2) GHz will be an important future probe for detecting the species in space.