RESEARCH
TECHNIQUE. Dr. Eric Forster of Esso Research and Engineering has developed a technique that allows measuring the
specific conductance of benzene in the bulk of the liquid. He concludes that conduction is based on electron transfer
Benzene Conducts by Electron Jumping Temperature dependence of conduction mechanism is a bulk property, doesn't depend on impurities, Esso data show
EQUIPMENT. One of the cells used in studying the mechanism of conduction in benzene is shown here. The mechanism's temperature dependence does not involve impurities in the sample; it's a bulk property, Dr. Forster says 44
C&EN
JAN.
8f
1962
Electrical conduction in liquid and solid benzene is apparently based on an electron transfer mechanism (electron "jumping"), according to data gathered by Dr. Eric Forster of Esso Research and Engineering's central basic research laboratory, Linden, N.J. Excited, delocalized 7r-electrons—especially those in the lowest triplet s t a t e seem to b e involved in the conduction process. The temperature dependence of the mechanism, the Esso scientist adds, doesn't depend on impurities; it's a property of the bulk of the liquid only. The Esso work shows that increase in conductance as temperature increases is caused by one of two processes: greater ease of electron transfer due to more extensive orbital overlap, or an increase in the population of conducting electrons. In benzene^ the first mechanism is the one that probably predominates. But in a hydrocarbon such as pentacene, for
example, the second mechanism is the dominating one. In other tests, Dr. Forster finds that activation energy for solid benzene is the same as that for liquid. The only difference between the two states is the level of conductance, which increases about 10 times when the benzene is melted. To eliminate the possibility of benzene's conductance being due to some easily ionizable impurities, the Esso scientist determined that the relative concentration of these ions has to be more than 1 0 _ 7 mole per mole of benzene. This, he says, is ruled out by the high purity of the samples used. In such high concentrations, impurities would cause higher conductivity than that which has actually been observed in benzene. Support. After comparing his findings on benzene's photoconductance with those of others, Dr. Forster says the hypothesis that conduction involves the triplet state is supported. The other work shows that oxygen-free benzene doesn't absorb appreciably between 2900 A. to 3600 A.; when benzene is saturated with oxygen, however, absorption in this region is considerable. This was formerly attributed to oxygen's making possible the normally "forbidden" transition from the singlet ground state to the first excited triplet state. In terms of this explanation, Dr. Forster says, his results show that benzene conductance follows population of the triplet state. Conductance of oxygen-free benzene is unaffected by irradiation. With oxygen, though, conductance increases because the triplet state becomes easier to populate. UV causes additional singlettriplet transitions, and conductance increases still further. When the light is turned off, conductance drops. With this idea, he calculated activation energy for a number of aromatic hydrocarbons. The calculated values agree fairly well with determined values in a majority of cases (seven out of 11). He cautions, however, that the possibility of incorrect experimental results exists because of the many experimental difficulties encountered in this kind of work. Whether positively charged molecules exist in the material is difficult to learn, Dr. Forster adds. But he feels that only electrons—not "holes"— are transported to the electrodes, since the potential drop at the cathode is greater than at the anode.
COMMENT:
A Scientific Society—The Beginnings
In this season 21 years ago, my colleagues and I were doing the experiment which resulted in the discovery of plutonium. Needless to say, my world has not .been the same since. Nor has my experience been unusual. The same forces operating in my case have markedly altered the lives of many millions of people and, indeed, society itself. Allowing for the lack of perspective that accompanies our closeness to the events, it still seems pardonable to judge the past two decades to be one of the most portentous periods in human history. And this has been made so by science and technology. I believe these things to be true not alone because of the novel dilemma revolving about nuclear weapons and the very survival of modern civilization; but also because of the general scientific-technological progress most dramatically exemplified by the peaceful atom and space exploration. What is perhaps more important in the long run, granted our ability to avert total nuclear war, is the fact that in these two decades science and technology have become a dominant force in our social order. . . Although it is in its infancy, the scientific society has arrived; it has crossed the threshold in its relationship to society as a whole. Science and technology are now part of the fabric of Government, industry and business, and of our social institutions. The destinies of individuals and peoples are irrevocably associated, from day to day, with the growth and use of scientific knowledge. .. . In the past two decades, then, science has come to stay. . . Government, business, and industry are dependent for survival and expansion not alone on technology, but upon an accelerating growth of knowledge deriving from research that once was sometimes described as "pure". . . The new relationship between society and science is reflected in the spectacular growth of the numbers of people who are doing research and development or who play supporting roles in these efforts. It is to be seen in the federal budget for research and development. . . Even more important are the new attitudes—of society in general toward science, and of scientists toward society. . . The enormous impact of the past
two decades on the scientific community reflects significant integration of science into society. I do not detect any qualitative change in the spirit of scientific inquiry, fortunately. But it would appear that there is an important alteration in the attitude of scientists about the relationship of their work to the larger social environment. Many of us' can recall a fairly general feeling of pride among scientists in the isolation of their work from the practical affairs of men. Indeed, it was not difficult to find resentment at any implication that a piece of research should have more than the remotest connection with application. Now, with the reduction of the time gap between basic and applied research, and with growing general appreciation of the value of knowledge, scientists seem more willing to relate themselves and their work to social objectives. . . . . . I do not wish to give the impression, however, that I believe this new kind of society is the property of science. We cannot, of course, proceed intelligently without integrating into our thinking and our acting the full range of human wisdom. . . I have asked primarily for men generally, and intellectuals in particular, to return science to the fold of humanism. It is unthinkable that a democratic-scientific society could evolve constructively without a wide endowment among its people of art, music, history, literature, and social dynamics. We can hardly discuss the future of the scientific society without relating it to the world struggle and the terrible dilemma confronting man as the result of the development of nuclear weapons. . . I believe each of us, scientist and nonscientist alike, must be aware of the importance of his own effort to the preservation of a libertarian society in the continuing crisis. Each of us needs a sense of responsibility and urgency—for the total of our efforts will be decisive, however remote from combat our work may seem.. We must not do too little. We cannot delay. . . We must act. . .
Dr. Glenn T. Seaborg, Chairman, U.S. Atomic Energy Commission before the American Association for the Advancement of Science, Dec. 27, 1961. JAN.
8, 1962 C & E N
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