Dr. Manfred Eigen in his laboratory in 1967, the year he won the Nobel Prize in chemistry. (Schlagmann/AP)

Manfred Eigen, who shared the 1967 Nobel Prize in chemistry for showing how to measure the speeds of reactions that had seemed impossibly fast, died Feb. 6. He was 91.

His death was announced by the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany, which Dr. Eigen founded in 1971. The institute did not say where or how he died.

Dr. Eigen was sometimes said to have measured the immeasurable. He was credited with helping to reveal the intimate details of chemical reactions that occur within time periods so brief as to seem all but nonexistent.

In chemical reactions, individual elements or compounds combine to create new compounds. But the time scales over which that combination occurs vary widely. Metal may rust over weeks or months; explosive reactions involving gunpowder or dynamite happen so rapidly as to seem instantaneous.

Such reactions were described as “immeasurably fast.” For many researchers, uncovering their secrets seemed beyond the reach of science. In speaking in English of these reactions, Dr. Eigen groped at times for a way to characterize their swiftness. At a lecture in Britain, he used to recall with amusement, he was advised to call them “damned fast reactions.”

Time intervals in these reactions are on the order of millionths or billionths of a second. Some are even faster. But according to the Planck Institute, Dr. Eigen “was firmly convinced that nothing in chemistry was immeasurable” and that the problem was a matter of developing and applying the proper techniques.

“Perhaps more than anybody else, Manfred Eigen understood how to think out of the box and successfully pursue new scientific directions,” Herbert Jäckle, the institute’s emeritus director, said in a statement.

Dr. Eigen’s breakthrough was developing the process known as chemical relaxation. In essence, this entailed applying a quick nudge — a jolt of energy — to a chemical system that had settled into equilibrium. Much of his work entailed beaming high-
frequency sound waves into chemical systems.

The jolt pushed the system out of balance, and the term “relaxation” connoted its settling back into stability. From spectroscopic measurements of the energy absorbed by the system, it was possible to learn the parameters of extremely rapid reactions.

Manfred Eigen was born in Bochum, Germany, on May 9, 1927. His father was a chamber musician, and Manfred developed a lifelong affinity for music, ultimately choosing science over piano.

World War II interrupted his formal education. At 15, he was pressed into service in an anti­aircraft unit.

Near the end of the war he was taken prisoner by the Allies. But he escaped with relative ease, he said, and tramped across defeated Germany for hundreds of miles.

It was not aimless wandering. In 1945, at 18, he turned up at the renowned University of Göttingen, one of the citadels of science. Although lacking some of the necessary documentation, he was admitted after he demonstrated his knowledge on an exam, and was said to be in the university’s first postwar class.

Physics was his first choice as a field of study, but because older returning soldiers got priority, he enrolled in geophysics. In due course he received his college degree and began working toward a doctorate in natural sciences, studying under professors such as Werner Heisenberg, a quantum pioneer who developed the uncertainty principle.

Dr. Eigen received his PhD in 1951, and three years later he presented the results of his prizewinning research at a meeting of the Faraday Society in London. According to the Planck Institute, his findings demonstrated for the first time that it was possible to determine rates of chemical reactions that occurred during time intervals as brief as a nano­second.

In 1967, Dr. Eigen received half of the Nobel in chemistry; the other half of the award was shared by Ronald George Wreyford Norrish and George Porter. All three were honored “for their studies of extremely fast chemical reactions,” the committee said in its citation, “effected by disturbing the equilibrium by means of very short pulses of energy.”

Dr. Eigen’s work helped solve major problems in physical chemistry, according to the Planck Institute, and also aided in the understanding of chemical processes that occur in living organisms.

In later years, he explored the biochemical roots of life and evolution. Despite some resistance to his plans, he was credited with helping create a multidisciplinary program at the Planck Institute to study the underpinnings of life at the molecular level. His work was hailed for creating a new scientific and technological discipline: evolutionary biotechnology.

Dr. Eigen had a son and daughter from his marriage to Elfriede Müller. He later married Ruthild Oswatitsch, his longtime scientific partner. A complete list of survivors was not immediately available.

Correction: An earlier version of this obituary imprecisely referred to chemical reactions. Individual elements or compounds combine to create new compounds, but not new elements. The story has been updated.