Infrared spectrum of the OCS-He complex

The weakly-bound van der Waals complex OCS-He has been observed by infrared spectroscopy in the region of the OCS nu (1) vibration (approximate to 2062 cm(-1)) in a pulsed supersonic jet expansion using a tunable diode laser probe. The results are in good agreement with previous microwave observations of OCS-He, but they extend to the vibrationally excited state, as well as to a considerably larger number of rotational levels with higher J-values. Prominent a-type transitions (DeltaK=0) are observed, together with weaker b-type transitions (DeltaK=+/-1). The rotational energy level pattern in the excited vibrational state is quite similar to that in the ground state, and the band origin is slightly blue-shifted (+0.111 cm(-1)) from that of the free OCS molecule. These results are of special interest due to recent observations in the same spectral region of OCS molecules trapped in ultra cold helium droplets. (C) 2001 American Institute of Physics.