DISTORTION IN ASYMMETRIC TOP MOLECULES 363comparable with the over-all efficiency of the most efficient phosphors, indicating that its lower over-all efficiency is due to a small percentage of radiative recombinations. C. GeneralWhile this work was in progress, two other papers reporting the evaluation of the electron mobility in cadmium sulfide by combined photometric and photoelectric measurements appeared. 12,13 In each of these the analysis depends upon the assumption of detailed models incorporating the bimolecular recombination law. By measuring the ac component of the photocurrent produced by modulated ultraviolet excitation, 12

Thermoelectric power measurements have seldom been used to investigate the photoelectronic properties of semiconductor crystals. This paper presents the results of an exploratory investigation of thermoelectric power in three different specific situations: (1) the effect on thermoelectric power of extrinsic photoexcitation involving imperfection states in the crystal, (2) the effect on thermoelectric power of optical quenching of photoconductivity, and (3) thermally stimulated thermoelectric power, associated with the emptying of electron and hole traps in the crystal. The increased sensitivity of the thermoelectric effect to two-carrier phenomena as compared to the Hall effect, makes it a valuable effect for investigating the contribution of electrons and holes to photoelectronic behavior. The results obtained with single-crystal CdS suggest that: (1) The thermoelectric effect is quite useful in imperfection-level spectroscopy, (2) Sensitizing imperfections for photoconductivity have a complex dipole-like structure, and (3) Holes play a larger role in photo-electronic effects than commonly attributed. Further investigations of the techniques using thermoelectric power are certainly indicated.

From measurements on the fine structure of the / = 0-*4 rotational transition of H 3 B 10 CO near 17,960 Mc/sec. we are able to establish that the spin of B 10 is 3 as had previously been reported by Gordy, Ring, and Burg. A quadrupole coupling constant of 3.44±0.1 has also been determined for this molecule. A brief description of our spectroscope is included.

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