Cyanoacetylene-doped \textit{ortho}-hydrogen and \textit{para}-hydrogen clusters studied using rotational spectroscopy

A high-resolution Fourier transform microwave spectrometer was used to measure the rotational spectra of the \textit{ortho}H$_{2}$ -- HCCCN and \textit{para}H$_{2}$ -- HCCCN dimers as well as larger (\textit{ortho}H$_{2})_{N}$ -- HCCCN and (\textit{para}H$_{2})_{N}$ -- HCCCN van der Waals clusters ($N$ = 2 and greater). To generate the clusters, low concentrations of HCCCN and H$_{2}$ (normal or enriched \textit{para}H$_{2})$ in helium are used at pressures up to 70 atm. The helium supersonic jet expansion into the spectrometer cavity/sample cell produces a collision free environment where the clusters are stabilized and studied. Varying the backing pressure, sample concentrations and/or nozzle temperature can control cluster size. The doped \textit{para}H$_{2}$ clusters are of particular interest because \textit{para}H$_{2}$ is suspected to exhibit the bulk property of superfluidity, similar to $^{4}$He. The study of the successive solvation of HCCCN with H$_{2}$ molecules may provide evidence for superfluidity in doped H$_{2}$ clusters.