Observation of P1-D1, P1-F1,3, and P1-H1,3 motional Stark-effect-induced anticrossings in He4: Determination of zero-field level separations

Anticrossing induced by the motional Stark effect created by atoms moving perpendicular to a strong magnetic field have been observed in He4. These anticrossings couple the n P1 state with the nominal n D1, n F1, n F3, and n H1,3 states via first-order (for the D1) and second-order Stark effects. The theory is derived to explain the line shape in the second-order case. This theory, along with the previously existing first-order-effect line-shape theory, is used to obtain the zero-velocity crossing points. These values are used in a leastsquares fit to determine the zero-field intervals. The nP1-D21 interval is determined precisely for n=6, 7, and 8 and the nG1-nHav interval is determined for n=6 and 7. A power-series expansion establishes the n P1 energy levels with respect to the higher nL states with high precision.