Detection of the millimeter wave spectra of the weakly bound complexes He-3-CO and He-4-CO

For the first time, millimeter wave absorption spectra of the van der Waals complexes He-3-CO and He-4-CO were detected in a supersonic jet. Altogethe r four rotational transitions of He-3-CO and six rotational transitions of He-4-CO were recorded between 110 GHz and 127 GHz with an intracavity spect rometer based on the millimeter wave generator, called OROTRON. The obtaine d results were included in a global fit together with previously known data enabling a more precise determination of the energy levels of the He-3-CO and He-4-CO complexes. In extremely cold, dark, and dense interstellar clou ds the He-CO complex may have astrophysical relevance. (C) 2000 American In stitute of Physics. [S0021-9606(00)00907-7].