Experimental and theoretical characterization of the long-range interaction betweenHe*(3s) and He(ls)

摘要

The long-range interaction between ~(1,3)S He*(3s) and ~1S He(1s) was studied in bulk liquid helium by fluorescence measurements and by combined theoretical electronic structure and bosonic density functional theory calculations. The excited He* atoms were produced in the liquid by corona discharge with subsequent impact excitation instigated by hot electrons from the discharge. The long-range contribution to the repulsive "hump" near 5 A in the ~(1,3)S He-~1S He potentials was interrogated by monitoring He* ~(1,3)S(3s)→P(2p) fluorescence profile characteristics as a function of external pressure between 0.1 and 3.5 MPa. Fluorescence line shifts and widths as a function of pressure were extracted from the experimental data and compared to the theoretical predictions, establishing that the nascent He* atoms reside in a bubble state within the liquid. It was observed that the experimental data could only be consistently reproduced if the excited He* atoms emit in a less-dense environment as compared with the rest of the bulk liquid.