1984

At school my interests were in history, politics and science. Since my older brother went on to study history and politics at the university, I decided that I would study chemistry. I never felt ordained for a career in chemistry, and I never abandoned my keen interest in history and politics.

At first science at the university was a disappointment to me. In the laboratory I found that it was necessary to follow procedures that had not been fully explained (if, indeed, the explanations were known) in order to obtain the 'right' result. Out of curiosity I would vary the method from that given in the laboratory manual, with the consequence that I routinely got the 'wrong' result. All this was symptomatic of the fact that I lacked the discipline to learn, or at any rate to learn with any degree of pleasure, the large number of rules that one must master before one can play the game of science.

The rules of this magnificent game are a hundred times more complex than those of chess. But who would choose to play such a game, I wondered. Without any great enthusiasm, I persisted through some years of training, often reaching outside of science for the intellectual stimulus, excitement and relevance to the world's great problems, which science seemed to me to lack.

Slowly, however, by doing science I came to be captivated and engrossed by the beauty of the subject matter and the thrill of the challenge that it offered.

Today, I retain my interest in history and particularly my concern for the grave political questions with which late twentieth-century man is faced, but now I begrudge the time spent away from the excitement of the laboratory and the fellowship of the international community of scientists to which I belong.

This is a peculiar story for a scientist to give of the birth of his interest in his subject. It happens to be my story, and may serve to illustrate that in the choice of a career, as in other major decisions, a lifelong commitment need not start with a love affair.

I have given an account of how I became a scientist, but have said nothing about my choice of speciality. Here my story may be more commonplace. Chemistry was the field in which I felt at home. My father was for a major part of his career a chemist, and so the sight and smell of a chemistry laboratory was lodged in my subconscious. At a more rational level, I found in the course of my studies that physics was too arid for my tastes—too close to the abstractions of mathematics—whereas biology, for all the appeal of living systems, seemed lacking in quantitative structure. This was a personal assessment based on a wealth of ignorance. I would not care to defend that judgement today, but it turned out to be a suitable one for me several decades ago.

As I advanced through my undergraduate years I had more decisions to make. I chose to concentrate on that part of chemistry that makes the greatest use of the methods of physics; 'chemical physics' (by convention this is somewhat to the physics side of 'physical chemistry').

Chemistry in the first half of this century tended to concentrate on the bulk properties of matter. In particular the rates of chemical reactions (which I studied as a graduate student from 1949-1952, working toward a doctorate at Manchester University in England) were studied as a function of concentration and temperature. The reacting species—the individual atoms and molecules—by contrast, have no such properties as concentration and temperature; they are described by their energy states of translation vibration, rotation, and so forth.

It was as if the chemists were sociologists, dealing with the behaviour of societies, and the physicists were psychologists recognising only the rules of behaviour for individuals. It was evident in the early 1950s that the time was ripe for a melding of these viewpoints; if each constituted such a powerful system of thought alone, they would be still more powerful in conjunction.

All this is clearer in retrospect than it was at the time. Nonetheless hints of this new direction in chemical physics, and particularly in the treatment of chemical reaction rates, were readily apparent in many discussions I heard as a graduate student. These discussions provided me with the underlying direction of my interests for my entire time in science.

Subsequently as a Postdoctoral Fellow at the National Research Council in Ottawa and at Princeton University, in my reading, in the calculations that I attempted, and the experiments on which I embarked, I was looking for ways of relating the rates of chemical processes to the states of motion of the colliding molecules. It turned out to be easier initially to look at the motions of the newly-born products of chemical reaction, than to control those in the reagents. Fortunately these types of information are complementary since one can, so to speak, run the movie of a reactive collision backwards, whereupon the products become the reagents.

On arriving at the University of Toronto in 1956, I suggested to my first graduate student, Ken Cashion, that he look for the motion of hydrogen chloride molecules newly born in the reaction of atomic hydrogen with molecular chlorine. The reaction

H + Cl₂ HCl + Cl

was known to be strongly exothermic (200 kJ/mole of energy is liberated when the strong HCl bond is formed). It followed that there must be vibration and rotation in the new-born HCI molecule, with the balance of the energy present as relative motion (i.e., translation) of the HCI and the Cl. What was entirely unknown was the apportionment of the reaction energy among these three types of motion. If this information could be obtained then one could start to picture the pattern of molecular motion involved in the act of chemical reaction.

The apparatus that Ken Cashion constructed consisted of an electrical discharge in a tube containing H₂; the H₂ dissociated in the discharge to give hydrogen atoms. The H atoms then flowed down a short tube to a point where they encountered a jet of molecular chlorine. The reaction H + Cl₂ ensued, at low pressure (~10^-4 atmos.) so that the newly-formed HCl product would, we hoped, emit radiation prior to being robbed of its energy in collisions.

The emission, we knew from molecular physics, would be in the infrared (at a wavelength ~3 ). In the first experiments the reaction zone was viewed by means of an infrared spectrometer through a sodium chloride prism, using a sensitive thermocouple as detector.

With the reagents flowing, there was no visible emission whatever from the reaction zone. However, when Ken Cashion scanned the prism through the angles corresponding to the range of wavelengths from 2 to 4 a broad peak was traced on the chart recorder attached to the thermocouple; HCl was being formed by the reaction in a range of vibrational energy states indicative of a highly specific motion in this new-born molecule.

As the recorder traced the infrared chemiluminescent spectrum of HCl Ken Cashion, having been recently ordained as a priest, felt that he should keep his excitement within the bounds of propriety, so he merely beat on the top of the spectrometer with his fists while shouting, "Holy crowbar!".

These experiments were reported in 1958 (Journal of Chemical Physics, 29, 455). The paper concluded with the sentence: "The method promises to provide for the first time information concerning the distribution of vibrational and possibly rotational energy among the products of a three—center reaction."

This work took its place in the early stages of development in laboratories around the world that led to the establishment of a new field called 'reaction dynamics'—the study of the motions of molecules in the course of the molecular collisions that we call 'chemical reaction.'

For further Autobiographical Information on John Polanyi go to that section of his website at http://www.utoronto.ca/profile/