Laser magnetic resonance spectroscopy of normally forbidden transitions: Electrostatic fine structure of the n=9, L=1--8 /sup 4/He singlet states

Forbidden transitions have been observed from the 7 /sup 1/S state of /sup 4/He to the manifold of states, n=9, L=1--8. These transitions are tuned into resonance with CO/sub 2/ laser lines by an applied magnetic field of 0--140 kG. Transitions to the odd-parity states are characterized by a velocity-dependent, motional Stark effect line shape which has been described previously. Transitions to the even-parity states have, in addition, a velocity-dependent transition moment creating a more complex line shape whose form is derived in an adjoining article. Analysis of the positions of over 20 observed resonances allows a determination of the zero-field separations of all the n=9, L=1--8 states of He, and the quantum defects for He singlet states with L>0.