#### Abstract

In the first paper of this series, the shift of the $2{}_{}{}^{2}{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ level of hydrogen was determined to be 1000 Mc/sec. A new apparatus differing from the original one in details, but not in principle, has been built in order to improve the accuracy of the above result. This provides a greater yield of metastable hydrogen atoms, a more homogeneous magnetic field, and more accurate means of measurement of magnetic field and frequency. With these improvements, preliminary measurements of considerably increased accuracy have been made on both hydrogen and deuterium. The transitions observed were $2{}_{}{}^{2}{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, $m=\frac{1}{2}$, to $2{}_{}{}^{2}{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, $m=-\frac{1}{2}$, as well as to $2{}_{}{}^{2}{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$, $m=\frac{1}{2}$ and $m=-\frac{1}{2}$. The first transition permits observation of the hyperfine structure of $2{}_{}{}^{2}{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, as well as an accurate calibration of magnetic field. Hyperfine structure was also resolved for the last transition in hydrogen. There was no observable difference between the level shifts for hydrogen and deuterium which may be taken as 1062±5 Mc/sec. Later papers of this series will deal with the numerous experimental and theoretical corrections necessary to obtain a level shift accurate to 1 Mc/sec.

DOI: http://dx.doi.org/10.1103/PhysRev.81.222

- Received 29 September 1950
- Published in the issue dated January 1951

© 1951 The American Physical Society