Grant: Research Tools and Instruments - Category 1 (<$150,000)

'Superfluidity' is a collective term for the fascinating properties (e.g. vanishing viscosity) and unusual effects (e.g. fountain effect) which bulk helium exhibits below its transition temperature of 2.17 K. Superfluidity is a manifestation of quantum effects on the macroscopic scale and requires that the microscopic constituents are bosons, i.e. have an integer composite spin. Besides helium, there is only one other system which may show superfluid effects, namely molecular hydrogen, H2. Hydrogen occurs as two spin modifications, paraH2 with total spin I=0 and orthoH2 with I=1. paraH2 is expected to have the higher transition temperature to superfluidity (7 K) because of its weaker intermolecular interactions compared to orthoH2. However, superfluidity in bulk paraH2 has thus far escaped experimental verification because it solidifies already at 13 K. We are currently pursuing a research program to detect microscopic superfluidity of paraH2 in clusters of the type (H2)N-molecule, where N is the number of hydrogen molecules. In our rotational spectroscopic investigations, we anticipate a 'turnaround' of rotational constant B of the clusters with increasing n, similar to what we have observed in (helium)N-molecule clusters. This research is currently hampered by two serious shortcomings of our microwave Fourier transform spectrometer: its narrow bandwidth and the difficulty to obtain reliable intensity information. Very recently, the area of microwave spectroscopy has been revolutionised with the development of the Chirped Pulse Broadband Fourier Transform Spectrometer by the Pate group at the University of Virginia. We request funds for the construction of such spectrometer to be able to further pursue our hydrogen cluster research with the exciting prospect to find the long sought after experimental verification of hydrogen superfluidity.