Computers help chemists produce movies A relatively new development in the production of motion pictures is the use of computers in making animated films. And a smattering of chemistsfinding computer-animated films to be useful research as well as pedagogical tools—are becoming movie producers. The stars in their films include atoms and diatomic molecules colorfully pulsating and oscillating, colliding and reacting; complex proteins coiling in simulated intricacy; and quantum mechanical wavicles gracefully illustrating and invigorating the mathematical expressions of, for example, Heisenberg's uncertainty principle. Scientist-movie producers gathered in Miami Beach, Fla., late last month to show and view the latest in the genre. The occasion was a symposium on computer animation in chemistry, sponsored by UAIDE (Users of Automated Information Display Equipment). And 10 days ago a computeranimated film festival played to a packed house at California Institute of Technology. Among the many films shown by different groups at Miami Beach, one that started out as a research tool for creating and recording visual images from model calculations and turned out to be research stimulating was shown by Chris Parr from the chemistry department of University of Toronto. In a study of reaction dynamics, Dr. Parr, with Prof. John C. Polanyi's group at Toronto, programed an IBM 360 computer to calculate potential energy surfaces in an extension of the London-Eyring-Polanyi-Sato method, giving trajectories, for example, for an atom on a collision course with a diatomic molecule under various sets of conditions. Data such as bond distances, Morse potentials (expressions of the relation between bond length and potential energy of a molecule), masses of atoms, and measures of translational, vibrational, and rotational energy were plugged into the computer. A mechanical plotter drew the individual frames of the movie in 2- by 3-inch pictures that were then photographed with a home movie camera. Unexpected. In one simulated reaction, a chlorine atom (C1A) and a hydrogen chloride molecule (HC1P)) approach each other on the screen. As they collide, the hydrogen atom is pulled away from Clr> by C1A. But then HC1 A goes into a rotational whirl and the hydrogen atom gloms on to its former partner C1B. So there is no net reaction. This little dance with a double exchange of partners was not expected from the Toronto group's re46 C&EN NOV. 9, 1970
search and would have gone unobserved had the film not been produced. The model calculation for this particular sequence was designed to produce the endothermic reaction: HC1 + CI -» H + Cl 2 and the reaction was not expected to go. In general, Dr. Parr says, endothermic reactions require high vibrational excitation in the molecule under attack. The computer was told to give the HC1 molecule a lot of vibrational energy in this sequence, and it did. But because hydrogen is much lighter than chlorine, anomalous behavior in the form of a light atom mass effect was expected to result in no reaction, regardless of the high degree of vibrational excitation. That is, the net outcome, zero reaction, was expected. But the reaction that sums up
In selected frames from "reaction dynamics" film by Toronto's Chris Parr and John Polanyi, CI and HCI go into a whirling dance. H (colored) changes partners twice. Net result: no reaction
CI + HC1 - * C1H + CI -> C l - f HC1 did occur and by an unexpected mechanism. Further research is necessary to determine the statistical significance of this odd mechanism, Dr. Parr says. Chemical physicist Kent R. Wilson, chairman of the symposium, points out that the essence of chemistry is shape >, or form and changes in form. The J fact that the upcoming generation has g been thoroughly steeped in visual im- '^ San Diego's Kent R. Wilson agery—with an attendant lessening in reliance on written communication— The essence of chemistry is form shouldn't be overlooked by purveyors of chemical messages. And producers added, though again computerized, of computer-animated chemistry films dimension. Action in the films is acare zealous proselytizers who welcome companied by sound track music requests for copies of their epic profrom a Moog synthesizer—an analog ductions. computer that produces musical forms. In production of "A Protein Primer" Computer-animated films of natural x-ray crystallographic data giving the and theoretical objects and processes dimensions needed to describe myocan carry messages from a professor globin (a protein that is active in supto his students, from a scientist to his plying oxygen to muscle tissue) were peers at professional meetings, or from provided to the computer. The comthe scientist's data through the compuputer was then instructed to build up ter and back to the scientist to afford the structure in a stepwise manner, him a visual, though perhaps intuitive, rotating fragments—the backbone, the grasp of his work. alpha helix, the heme group with its Entertaining. The role of a comoxygen-holding iron—to show their inputer-animated film as an attention tricate structures. The computer then getter was aptly demonstrated at the put together the complete myoglobin symposium in Miami Beach and at molecule, zooming in on the active the Caltech film festival by represensite to show in detail the region where tatives of The Senses Bureau in the oxygen is bound, then climbing back department of chemistry, University out of myoglobin for a view of the of California, San Diego. "Photodisentire structure rotating eerily in free sociation of ICN" and "A Protein space. This action was ultimately Primer" by Robert Weiss, Kent Wildisplayed on a cathode ray tube and son, Fred Heidrich, and Noël Bartlett photographed frame by frame. The of The Senses Bureau, simulate a phoMoog sound track was then added to tochemical reaction and the structure complete an enthralling package. of myoglobin. These films have an
