Submillimeter detection of the van der waals stretching vibration of the Ar-CO complex

With the Cologne submillimeter-wave supersonic jet spectrometer, we extende d molecular jet spectroscopy with backward wave oscillators up to frequenci es of about 600 GHz. For the first time, the van der Waals stretching vibra tion of the Ar-CO molecular complex was detected in direct absorption. We m easured 13 re-vibrational transitions (upsilon(stretch) = 1 <-- 0, K-a = 0 <-- 0) in the frequency range from 528 to 600 GHz and additionally the two R(3) K doublet (K-a = 4 <-- 3) pure rotational transitions at 447 GHz with an accuracy of about 200 kHz. The re-vibrational transitions were assigned and fitted within experimental accuracy to a simple Hamiltonian taking into account the Coriolis interaction between the stretching and bending states , i.e., between upsilon(stretch) = 1, K-a = 0, and upsilon(bend) = 1, K-a = 1 The intensity of the transitions in the van der Waals stretching mode wa s estimated to be a factor of 5-10 less than that in the bending mode of AT -CO. (C) 1999 Academic Press.