100 Years Ago, Elmer Imes’ Observations Informed a New Understanding of Molecular Physics

EMMETT WARREN, NEWS EDITOR, emmett.warren@photonics.com

One hundred years ago this month, physicist Elmer Imes published his dissertation, “Measurements on the Near-Infrared Absorption of Some Diatomic Gases,” in Astrophysical Journal. The paper provided the scientific world with the first accurate determination of the distances between atoms in molecules using his own customized spectrometers; expanded the range of applicability of quantum theory; and provided evidence for the existence of two isotopes of chlorine.

Elmer Samuel Imes. Courtesy of Wiki Commons.

Before 1919, however, Imes was already making a name for himself in the scientific community through his construction and improvement of spectrometers.

In 1916, working under physicist Harrison M. Randall at the University of Michigan, Imes began work that led to the design and construction of a series of infrared spectrometers of increasing resolving powers. His final and most precise spectrometer consisted of two devices working together: a prism spectrometer and a grating spectrometer. Imes used his instruments to measure absorption bands in the near-IR region for three hydrogen halides: HCl, HBr, and HF.

For his most detailed work, the HCl molecule, Imes found two absorption bands near 1.76 and 3.46 μm. His spectrometer was able to resolve the band at 3.46 μm into 12 pairs of peaks and the band at 1.76 μm into eight pairs. What Imes would discover is that peaks corresponding to transitions between quantized rotational energy states were superimposed on the spectral lines coming from the vibrational transitions of the diatomic molecules. This data, along with his unique spectrometer design and construction, served as the foundation for Imes’ doctoral dissertation.

In his essay “The Life and Work of Elmer Samuel Imes,” Ronald E. Mickens, a physicist at Clark Atlanta University and author of several works on Imes, writes, “As the foundations of physics made the transformation from a classical to a quantum worldview, physicists developed theoretical explanations for the unexpected band spectra. Several prominent theorists and experimentalists of the early quantum era did at least a portion of their work on molecular band spectra.”

According to Mickens, the observation of this transformation comes from an experimental point of view, for two reasons. “Under the guidance of Randall, Imes was able to construct and improve upon previous spectrometers,” Mickens said. In addition, Imes was able to conduct some of the first precision measurements of the rotational and vibrational spectrum of HCl, HBr, and HF. “There had been people, probably a decade or two before, who had tried to get the spectrum of these diatomic molecules, but they were either not very precise or their interpretation of the spectrum was such that very little useful information was obtained. The early interpretations were primarily based on classical mechanics.”

Due in large part to Imes’ early experiments, the shift in scientific circles to a quantum worldview brought about new applications and interpretations of experimental data. In fact, the thesis of Imes’ first paper predicted this eventual shift.

“There is found here a new application and test for the quantum theory in that it is extended to the originally excluded region of the rotational energy of molecules,” Imes wrote. Mickens noted that although Imes analyzed this data, it would take another few years before this data was fully interpreted and applied to other issues in molecular spectroscopy. Mickens said this was all about asking the right questions, which often occur in hindsight.

“Progress in science is determined after the fact,” Mickens said. “It generally is not determined while it is being done. What [Imes] did was he showed that these things do exist, and that they could be factually measured, and that you could use that data, for example, to measure the bond length between the hydrogen and the chlorine atoms.”

Imes’ measurements would provide the first accurate experimental proof that rotational energy was quantized. Due to his work, Imes was “quickly recognized as a major figure among the small group of researchers focused on spectroscopy,” Mickens wrote.

In 1974, Earle Plyler, a U.S. physicist and pioneer in the fields of IR spectroscopy and molecular spectroscopy, wrote that the universal applicability of the quantum theory was doubted across the scientific community at the time. “Some held it was useful only for atomic spectra,” he said. “Some held that it was applicable for all electromagnetic radiation. Imes’ work formed a turning point in the scientific thinking, making it clear that quantum theory was not just a novelty, useful in limited fields of physics, but of widespread and general application.”

Following Imes’ publication of his doctoral dissertation in November 1919, he co-authored “The Fine Structure of the Near Infra-Red Absorption Bands of HCI, HBr, and HF” with Randall in the same month. The paper was published in Physical Review the following year.

Mickens writes that Imes’ and Randall’s data for HCl was significant in that it showed each of the 12 peaks within the band located at 3.46 μm were split into two peaks: “That doublet substructure was soon given a compelling explanation by Adolf Kratzer and F. Wheeler Loomis, who interpreted the phenomena as the consequence of chlorine having isotopes of mass numbers 35 and 37.”

Imes’ ultimate goal was to teach physics and do research at the graduate level. But — despite his recognition and breakthroughs — he was professionally hindered because of his race. Without a job available in academia, Imes moved to New York for work in 1918, falling into the midst of a budding celebration of black American culture known as the Harlem Renaissance.

What is unique about the discrimination Imes faced professionally was that it was not seen the same way in every place. One of Imes’ former students at Fisk, Youra Qualls, would go on to earn a Ph.D. from Radcliffe College and became a professor of English at Langston University in Oklahoma. One day, a letter from Qualls arrived on Mickens’ desk. It was dated April 1982.

“I worked for Dr. Imes as secretary in either my junior or my senior year in college,” Qualls wrote. “At the time Dr. Imes was writing a history of physics. One of the delightful tasks I assumed was going through foreign science journals to note references to the work of ‘Imes of the U.S.A.’”

Qualls later recalled a conversation she had with the University of Oklahoma’s dean for the Graduate School of Sciences, Jens Rud Nielsen.

“As Dr. Nielsen and I talked, Dr. Imes’ name came into the conversation. He told me that he had become familiar with the work of ‘Imes of the U.S.A.’ during his student days in Denmark but that he had never known that Imes was a Negro.”

Those who knew of Imes in the U.S. were generally aware that he was black, but even if the world hadn’t, Mickens said it wouldn’t have made a difference, because his scientific work was valid. Physicists are still human, he said, and capable of discrimination. But they were also capable of separating the science from the scientist.

“You have to distinguish between the sociological aspects of it and the physical aspects,” Mickens said. “No one is going to throw away some valuable data, just because you’re black or female. They may steal it, they may not give you credit for it, but they’re not going to throw it away.”

Despite early setbacks, Imes would find satisfaction later in life. In 1930, after over 10 years in New York, he returned to Fisk University. At Fisk, he served as the chair of the physics department, revised the undergraduate programs, and eventually planned his own graduate program in physics.

While at the University of Michigan as a graduate student, Imes had found solace in his own research lab, which he used while working toward earning his Ph.D. William Swann, a friend and colleague of Imes from the Bartol Research Foundation at the Franklin Institute in Swarthmore, Pennsylvania, admired the research lab as “a mecca for those who sought an atmosphere of calm and contentment.” Swann later recalled that his colleague “could always be relied upon to bring to any discussion an atmosphere of philosophic soundness and levelheaded practicalness.” In 1935, due to his accomplishments as a graduate student, Imes was able to send three of his students to work at the University of Michigan to learn about innovative x-ray techniques.

While Imes’ observations were critical to the developmental understanding of molecular physics, Mickens noted that this was just one achievement during a period of great innovation, and it is difficult to concisely determine just how much of an impact his work had on its own. For example, just a few years before the publication of Imes’ dissertation, Einstein had published his general theory of relativity.

“History is a very complicated thing,” Mickens said. “This was a time where things were changing very fast.” Asking the right questions, Mickens said, is what leads to progress. The right questions are asked when the work is framed within a specific context. “There is no such thing as a truly objective fact. Facts are generated when data and interpreted within a certain methodology.”

The methodology of a black scientist contextualizes both the work of Imes, as well as his accolades.

“His work fits into what I would call the progress of science, based on data, that becomes more and more sophisticated and where the tools to interpret those data become more consistent,” Mickens said. “His work was just one of those things in the long march towards a better understanding of the physical universe through experimental work and theoretical interpretation.”

Imes’ story is a piece of history. But Mickens says the value of this sort of history is its essential understanding to the future of scientific progress. This is why he has concern for young scientists today.

To Mickens, the sociological problems in today’s scientific fields are not limited to the acceptance and validation of scientists from minority demographics, but his attention is now on fostering general interest in the intrinsic nature of science.

“Currently we live in an anti-science society,” Mickens said. “There is very little appreciation for science and technology. The relevant issue to me is whether we can prepare students — black, white, female, or otherwise — who can go into the sciences…It’s only been since probably the middle of the 20th century that scientists have stopped trying to understand the history of their discipline or science in general. I think science in general would prosper if people had an understanding of the genesis of their field and how it came to be what it is now. It wasn’t always that way.”