The results of a joint experiment aimed primarily at the determination of the frequency of the H1 hyperfine transition (F = 1, mF =O) cf (F = 0, mF 0) is reported. In terms of the frequency of the Cs133 hyperfine transition (F = 4, mF = 0) c-* (F = 3, m F O), defined as 9192 631 770 Hz, fortheunperturbedhydrogen transition frequency the value VH = 1420 405 751.768 HZ is obtained. This result is the mean of two independent evaluations against the same cesium reference, which differ by 2 X 10-3 Hz. We estimate the one-sigma uncertainty of the value vH also to be 2 X 10-2 Hz. One evaluation is based on wall-shift experiments at Harvard University; the other is a result of a new wall-shift measurement using many storage bulbs of dflerent sizes at the National Bureau of Standards. The experimental procedures and the applied corrections are described. Results for the wall shit and for the frequency of hydrogen are compared with previously published values, and error limits of the experiments are discussed.

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Pulsed excibtion of atomic and molecular beam devices with separated Ramsey-type interaction regions allows the observation of signals due to very narrow atomic velocity groups. The theoretical background of this method is discussed. Experimental operation of a near mono-velocity cesium beam tube is demonstrated. The velocity distribution of a commercial cesium beam tube is obtained using the pulse method. The normal R,amsey pattern of this beam tube is calculated from the velocity distribution and compared with the measured Ramsey pattern. The pulse method allows the direct determination of the cavity phase shift and of the second-order Doppler correction in beam devices. The pulse method thus shows promise for the evaluation of existing laboratory as well as commercial cesium beam tubes with respect to these effects.