15min:

JULIE M. MICHAUD AND WOLFGANG JÄGER, Department of Chemistry, University of Alberta, Edmonton, AB, CANADA.

A high-resolution Fourier transform microwave spectrometer was used to measure rotational transitions of (orthoH₂)_N - HCCCN and (paraH₂)_N - HCCCN (N = 2 and greater) van der Waals clusters. The clusters are prepared using a gas sample containing low concentrations of HCCCN and H₂ (normal or enriched paraH₂ gas) in helium up to pressures of 40 atm. The helium supersonic jet into the spectrometer cavity produces a collision free environment where the clusters are stabilized and can be studied. Varying the backing pressures and sample concentrations controls the size distribution of the clusters. The measurement of rotational transitions corresponding to minor isotopomers of HCCCN (DCCCN, HCCC¹⁵N, ...) aids in the assignment of the N number. The N number assignment also benefits from the measurement of mixed paraH₂ and orthoH₂ clusters such as (paraH₂)(orthoH₂) - HCCCN. The paraH₂ containing clusters are of particular interest since paraH₂ is suspected to exhibit the bulk property of superfluidity, similar to ⁴He.