RESEARCH
Gaseous C Is Po!yafosnic Calculations from quantum theory show c a r b o n in v a p o r phase is in p o l y a t o m i c chains
vJASKor*» r\Riu>N at hi ill·, tempera turcs is associated predominantly into polyatomic molécules; it is not exclusively in the form of monatoinic carbon as luis been assumed. This unexpected result stems from theoretical studies by Dr. Kenneth S. Pitzer and Or. Enrico d e m e n t i at the University of California. Chemists have more or less assumed ihat gaseous carbon would be mostly monatmnic with a few diatomic molecules, because the temperature* would be high enough to iiiptuie t h e carboncarbon bonds. But no one really knew, and this lack oi knowledge limited the1 use of carbon at high temperatures. To fill this gap in knowledge, D r . H. A. Chupka and D r . M . G. Inghram a t University of Chicago undertook experimental work and found, t o their surprise, strong evidence for t h e existence of triatomic molecules and some indication of molecules with five carbon atoms in the vapor phase.
Now, in the third stage, the chemist is coming to think of quantum mechanics as another tool to be used to supplement laboratory work in those cases where its use is appropriate. The chemistry of carbon at high temperatures is such a case. With only one atomic species present, the complexities of computation are greatly reduced. Furthermore, Or. Pit/ier and Or. d e m e n t i were able to evaluate some of the more complex integrals empirically bum ^ j u l u u data on aromatic hydrocarbons.
SiC Emits Electrons Westinghouse finds silicon c a r b i d e can emit electrons with low p o w e r consumption
S I L I C O N CARBIDE (see p a g e 34)
turns
up also in news horn Westinghouse. Research physicists W. J. Choyke and Lyle Patrick of Westinghouses research laboratories have found that it can emit electrons directly and con£> Carbon Chains. It turns out that tinuously b o m its surface, could thus act as the cathode in a vacuum tube. the simple a n d obvious assumption of One of the big disadvantages of monatoinic· carbon was wrong. Wrong, vacuum tubes as they are built today, that is. under the conditions in which Westinghouse says, is that you need a they were interested and under the lot of power to heat the cathode conditions which the University of Chienough for it to emit electrons. Hut a cago workers employed, if the gas silicon carbide semiconductor with a phase is in contact with the solid phase p-n junction needs very little power in a closed system, it turns out that the and yields electrons instantly and inincreasing pressure is sufficient to predefinitely when a small voltage is apvent dissociation of the polycarbon plied with reverse bias across the juncmolecules up to high temperature. tion. According to the calculations of Escape of electrons from the siliDr. Pitzer a n d Dr. Clemen ti, there will con carbide is accompanied by emisbe relatively little monatomic carbon sion of visible light—a form of electroat 2500° C. or higher. Most of which occurs when the molecules are in the form of chains, luminescence enough voltage is applied to break and those with an odd number of atoms down t h e junction's electrical resistare more abundant. They calculate This light is concentrated in t h a t at 2500° K., average chain length. ance. > Quantum Mechanics, Obviously small, blue spots at the junction. T h e is 6.2 atoms. And, as though to demspots are small—about 130 microns something had to h e clone to clear u p onstrate that the chemical laboratory is across—but give currents up to one this puzzling situation. D r . Pitzer de- not obsolete. Dr. Pitzer has now undermicroampere, which is an electron dencided that the answer Mas a theoretical taken experiments to test the calculasity comparable to that from the stud\ using quantum mechanical methtions. cathode of a typical vacuum tube, ods. As Or. Pitzer points out, quantum Westinghouse points out. mechanics is now entering a third stage Although the Westinghouse research as a part of the working equipment of is in an early stage, the eompanv can the chemist. New DDT Behavior Noted already foresee many uses for this During the early days of the theory, phenomenon. It could b e a help in much labor was expended i n using it t o Variable results from use of D D T in miniaturizing cathode ray tidies, for compute spectra a n d other known data gonds, lakes, and other mosquito breedexample. Or you could build vacuum in order to verify t h e theory. When ing areas may be explained by a findtubes with many components in them confidence in the theory h a d become ing made in Orlando, Fla. Department and still not be faced with a major firmly established, t h e second stage was of Agriculture chemists and entomoloproblem in heat dissipation. And reached. Proponents of the theory gists have found that D D T at one part since the electrons come from almost cried happily, " T h e clay of the labora- per hundred million in water does not a point source, you could focus the tui y experimentalist i s over! W e can remain in a uniform suspension but electron beam readily. compute everything w e need to know codistills with evaporating water and Other semiconductors also exhibit wiiu quantum mechanical techniques." tends to concentrate at the surface and this property, the company adds. But But of course the- laboratories at the walls of containers. none have reached this high an electhroughout the w o r l d d i d not close This D D T behavior in water is a sur- tron density. Silicon itself and cesium their doors. For, says E>r. Pitzer, it prise, USDA says, because it has never on germanium, for example, give densoon became clear that i n most cases been noted before despite the extensive sities which correspond to about one the time and labor involved in comput- use of D D T for many years. In simi- micromicroampere. ing results would f a r exceed t h e time lar tests, other insecticides—parathion, Westinghouse points out that this and labor needed t o get t h e same r e - malathion, lindane, and dieldrin—did electron emission might help to bring not show this action. the vacuum tube back to popularity. sults experimentally. 36
C&ENAUG.
17,
1959
