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Experiments are reported on the microwave spectra of the free OH radical. The radicals are produced by an electric discharge in concentrations near 10% at pressures of approximately 0.1 mm Hg. The spectra are detected by Zeeman modulation. They are due to direct transitions between the A-doublet levels of each rotational state in the ground vibrational level of the molecule. Spectra due to 0 16 H, 0 18 H, and 0 16 D in II* and II* states have been observed in the 7.7 to 37 kMc/sec region. Intensity of the lines ranges from about 5X10~~6 cm"" 1 to 5X10 -8 cm"" 1 .Van Vleck's theory of molecular energies in 2 n and 2 S states is extended to include terms of order (E vo t or Ef s ) 2 /E e i 2 . The experimental results are in agreement with theoretical expectations to about one part in 2000 which is the order of accuracy of the theory. An improved agreement (to one part in 3500) is obtained if one allows a small variation (one part in 1400) of the electronic wave function from one rotational state to the next. The values of the molecular constants determined from the A-type doubling data are 4 2 (-l)*(n|4i y +2BZ y |S>(S|5L I ,|n>/(fe-£n) 2-states = -2361.37±2.95 Mc/sec in 0 16 H and -1548.99±2.10 Mc/sec in 0 16 D; 4 S (-l) s |(n|5L 2/ |S>| 2 /(^s-^n) = 576.18±1.64 Mc/sec S-states in 0 16 H and 161.94zbl.61 Mc/sec in 0 16 D; A/B = -7.444±0.017 in 0 16 H and -13.954±0.032 in O l6 D. The spectra include magnetic hyperfine structure from which the following values are obtained for parameters that describe the unpaired electron distribution in the molecule: and (1A 3 )AV= (0.75±0.25)X10 24 cm"* (sin 2 xA 3 )Av= (0.49±0.01) X10 24 cm~The hyperfine structure, the molecular magnetic moment and the line intensities are strongly dependent on the extent of intermediate coupling in agreement with theoretical expectations. The microwave spectrum can be used in studying chemical properties of the radical. Its lifetime was determined to be near J sec, and the effects of certain substances on radical concentration were examined.

Theory and experiment are presented for the drag exerted on electrons in a solid by a traveling ultrasonic wave. After a discussion of the reasons why the effect is generally very small, it is shown that under certain conditions in w-type germanium it may be quite appreciable, and that its size directly indicates the intervalley scattering rate. Experimental data are given for arsenicdoped germanium ranging in impurity content from 10 14 to 10 16 cm -3 , at temperatures from 20 to 160°K. These yield the absolute value of the "uniaxial" deformation potential constant (16 ev) and the intervalley scattering rate as a function of temperature and doping. The interpretation of the results ascribes intervalley scattering action both to phonons and to impurities. The phonon contribution yields the frequency of the (100) longitudinal phonon (6.6X 10 12 sec" 1 ) and the size of the appropriate coupling parameter ; the impurity contribution yields intervalley scattering cross sections for neutral and ionized donors as a function of temperature. The two cross sections are explained as, respectively, being due to exchange scattering events and to compound capture-reemission processes. Further analysis gives a lower limit to the valley-orbit splitting of the arsenic donor ground state (1.7X10 -3 ev). The experiment verifies that the conduction-band valleys lie on (111) axes at the Brillouin zone edge. Ultrasonic attenuation due to intervalley scattering is discussed and is shown to be too small to be easily measurable.

through second order; clearly the result is causal on the r 0 scale and acausal on the r 2 scale.The nonadiabatic approximation implies the use of the fully causal Green's function. 5 The results for the two-body correlation function G (x, x x , v, t) = G 1 can be extended to s bodies. Writing c + ...+ S G i+ F, *= i where the index c in the second term denotes combinations of s -1 indices in s -2 places, it can be shown by induction that the s-body correlation function satisfies [d/dt + v-v]K lt2r .. tS . x = source term involving lower-order correlations, where terms of magnitude € or smaller in the s-body and higher correlation functions have been dropped. From this equation, we see that the exact Green's function for the s-body corre-lation is causal and of the same form as for two bodies. Our previous remarks on the Bogoliubov and time-scales approximations also extend without difficulty.We have confirmed the existence of a new negative carrier of high mobility in superfluid helium, reported by Doake and Gribbon, and determined its zero-field mobility. We suggest that it may be the negative helium ion in a small cavity in the liquid. A series of carriers with mobilities between that of the "fast" and the "normal" (electron bubble) carrier is also shown to exist.

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A measurement of momentum relaxation times for charged particles in liquid helium is reported. The method is to measure the change in the reflection coefficient of a microwave cavity caused by the admission of ions. The measured relaxation times can be combined with the known dc mobilities of the ions to yield values for the effective masses. Most extensive measurements were performed using positive ions in He II. A temperature-dependent effective mass, increasing from approximately 40 helium masses at 1.3 K to over twice this value near the lambda point is found. The data are shown to be consistent with the electrostriction model of the ion, including contributions to the mass from both normal and superfluid components. A core radius of approximately 6 ~t is shown to account both for the mass and for the mobility in the viscous flow region. Data on the negative carrier near 1.8 K yield an effective mass of 100 to 200 helium masses, and are consistent with the bubble model. The radius implied both by the mass and an analysis of mobility data in the viscous flow regime is 14 +-3 ft, quite consistent with the value deduced from other measurements. A measurement on the positive carrier in saturated (NBP) helium vapor indicates a mass of 75 +_ 20 helium masses. Both the mass and the mobility of this carrier are consistent with a droplet of radius 11 +_ 2 ~t forming on the ion. The theoretical droplet radius is 12.6 ~t.

be obtained by using 7rr 0 2 for oj and (2meg) 1/2 for p, with m near to the true mass of a He 3 atom. Then Eq.(2) becomes