Obituary of Peter Emil Siska

Peter Emil Siska, Professor of Chemistry at the University of Pittsburgh, died February 27, 2009.

Pete Siska was born in Evergreen Park, Illinois and received his B.S. degree at DePaul University. His graduate work at Harvard University, which led to his Ph.D. in 1970, was under the direction of Dudley Herschbach, employing the crossed molecular beams technique to study the reactions of alkali atoms with hydrogen atoms. He was particularly fortunate that Yuan Lee joined the Herschbach group in 1967 as a post‑doctoral associate and spearheaded the construction of the first “supermachine”, a universal crossed‑beams machine, which extended the technique beyond the study of alkali atoms for the first time. Siska followed Lee to the University of Chicago and spent the period 1969‑1971 there as his first post‑doctoral associate, studying the elastic scattering of noble gas atoms in exquisite detail with the crossed‑beams technique. It was there that Siska developed his interest in using this technique to probe intermolecular forces. At Chicago, he also participated in a landmark crossed molecular beam study of F + D2 in which vibrational states of the product HF molecules were detected for the first time from the observed angular distributions. In 1986, Herschbach, Lee and Polanyi shared the Nobel Prize in Chemistry for the development and application of this technique to studies of the elementary steps in chemical reaction dynamics.

Siska joined the University of Pittsburgh as an Assistant Professor of Chemistry in 1971 and rose to full Professor in 1991. He extended the range of the crossed supersonic molecular beam technique to the study of metastable electronically‑excited noble gas atoms. Over the years, he and his coworkers studied non‑reactive and reactive scattering by other atoms and small molecules. Through analysis of results and structure and dynamics calculations, they learned about the interatomic potentials and contributed greatly to the advance of knowledge in this field. As illustrated fully by his much‑cited 1993 review, Siska was equally comfortable and expert in the experimental and theoretical aspects of small molecule interactions. Experimentally, with the crossed‑beam technique, he was able to measure the angular dependence of scattered metastable noble gas atoms and of the product Penning ions and the energy spectra of the electrons resulting from the reaction, all over a range of collision energies. Using his knowledge of theory, his group derived complex interatomic potentials for metastable atom interactions, the “imaginary” part of the potential giving information on the autoionization of the transition state. He also developed a pseudopotential method for the calculation of potential energy curves.

Although his research was at the heart of his work, Siska saw himself primarily as a teacher. As well as guiding graduate and undergraduate students in their research, he made noteworthy contributions to the teaching of graduate, upper level undergraduate and Honors Freshman chemistry courses. His passion and gift for teaching were recognized by a Chancellor’s Distinguished Teaching Award in 1987 and a Tina and David Bellet College of Arts and Sciences Teaching Excellence Award in 2003. As might be expected, his graduate course on Molecular Dynamics was an inspiring experience for the class. His Honors General Chemistry course was rigorous and demanding, but most lectures were punctuated by thought‑provoking and often ear‑shattering demonstrations. After searching unsuccessfully for a suitable text for the course, he wrote his own book, University Chemistry, published in 2006. Siska also was working on a Physical Chemistry book and had completed several chapters before his death. He was also fully involved in service and outreach activities of the Chemistry Department.

Pete Siska was erudite and witty, quiet but not reluctant to engage in discussion of the latest research result. We are fortunate in having book reviews and a mock research proposal, which he sent to the American Physical Society, to aid us in remembering these qualities. He was also an accomplished artist and draftsman, as evidenced by the clarity of many of the diagrams in his textbook. Outside of chemistry, one of his main interests was classical music. Beginning as a violinist, he later was an active choral singer in local groups. Other interests included history, astronomy and travel.

Pete Siska is survived by his wife Jeanne and his children David and Sarah.

To honor Pete’s memory, donations may be made to the Peter E. Siska Fund for Undergraduate Research in the Department of Chemistry. Contributions earmarked for this fund may be mailed to: Office of Institutional Advancement, University of Pittsburgh, 500 Craig Hall, 200 South Craig Street, Pittsburgh, PA 15260 or made online at www.giveto.pitt.edu/ways/gift_of_cash.asp