Fine Structure and Zeeman Effects in Helium Band Lines

Second and third order grating photographs of helium ($\lambda \lambda 6400$, 5733, 4546 and others) having the $2{}_{}{}^3{}_{}{}^{}\Pi$ state as their final electron level show fine structures in the band lines. The $3{}_{}{}^3{}_{}{}^{}\Pi \to 2{}_{}{}^3{}_{}{}^{}\Sigma$ bands ($\lambda \lambda 4650$, 4670) show no evidence of fine structures in their lines. The observed results can be completely explained by assuming that each rotational level of the $2{}_{}{}^3{}_{}{}^{}\Pi$ electron state has a characteristic partially resolved fine structure, as shown in Fig. 3, but that the fine structures which presumably exist for the other electron states involved ($2{}_{}{}^3{}_{}{}^{}\Sigma$, $3{}_{}{}^3{}_{}{}^{}\Sigma$, $4{}_{}{}^3{}_{}{}^{}\Sigma$, $3{}_{}{}^3{}_{}{}^{}\Pi$, etc.) are much narrower and completely unresolved in our work. There are two types of fine structures in the $2{}_{}{}^3{}_{}{}^{}\Pi$ levels, one for the odd $K$ values ($A$ levels), another for the even $K$ values ($B$ levels). The theoretical interpretation of the observed fine structures as partially resolved triplets is discussed.