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  • Writer's pictureDale DeBakcsy

Spectral Lines from a Dying Nation: The Molecular Spectrometry of Hertha Sponer.

It is hard to imagine a time and place outside of Charles Dickens’s Revolutionary France that more embodies the spirit of the Best of Times and Worst of Times than early 20th century Göttingen. At its best, in the 1920s, it boasted a heady selection of the planet’s greatest mathematicians and physicists, clustered together to rewrite entirely the rules for atomic and molecular structure and behavior. At its worst, in the 1930s, it gave itself over to the anti-Semitic ravings of the rising Nazi party, and tore its magnificence to tatters in the name of party ideology and racial purity. The roll call of those who directly experienced those high highs and low lows reads like a roll call of the modern scientific pantheon: Max Born, James Franck, Emmy Noether, Maria Goeppert-Mayer, Richard Courant, Edward Teller, and Germany’s second ever woman to hold a professorship in physics, Hertha Sponer.


Historically, Sponer’s story has tended to get lost in the deep shadow of her contemporary Lise Meitner, whose tale features many of the same contours as that of Sponer, but with both the triumphs and tragedies amplified. We have decided which woman physicist victimized by the Nazi era and the systemic gender discrimiantion of early 20th century Germany we have chosen to remember, and it’s Meitner, thank you very much. And that’s rather too bad, because not only did Hertha Sponer do some gorgeous physics over the course of four personally challenging decades, but her story also highlights the rapid social change occurring in the Western world in the early 20th century, and how a professional and highly educated woman was able to successfully navigate that evolving culturescape.


Hertha Dorothea Elisabeth Sponer was born, the eldest of five children, on September 1, 1895, in the small east German (currently Polish) town of Neisse. Her family was of a Protestant background that highly valued education, and in her elementary school Sponer was exposed to an impressively broad array of subjects, including French, German, geography, natural science, writing, singing, arithmetic, religion, gymnastics, and needlework. Somewhere around the year 1906, her family moved to the town of Zittau, which still remains, if just barely, within the borders of Germany.



It was, for Sponer, an unfortunate move. The school in Zittau was not as advanced as Neisse’s, and Sponer believed that, between the slow pace and unchallenging material, she would never learn enough at Zittau to be able to take the Abitur, the competitive exam for the German university system, where her ambitions lay. As such, she downgraded her expectations for a life of scientific research to that of a workaday private teacher, and attended a governess training school, which she graduated from in 1913.


She worked as a governess for two years, and in the middle of World War I took up a substitute teaching appointment. If you’ve ever acted as a substitute teacher, you won’t be surprised by the fact that she did not remain long in that generally thankless profession and, in 1916, she made the decision to make up for lost time and attend a cram school for the Abitur. She worked hard, mastered the two year condensed curriculum in one year, and took the exam in March of 1917, excelling in its physics portion, and becoming one of only 570 women that year to pass. Her parents had expected, after the Abitur, that she would take up a position as a teacher at a girls’ secondary school, but after having read in a newspaper story about Sponer’s performance how remarkable it was to have passed the exam with so few years of preparation, they wrote to her proudly giving their full permission for her to undertake whatever university studies she liked.


Sponer began her university career at Tübingen University in May of 1917, but was quickly frustrated by the lack of theoretical physics courses on offer, or indeed any physics beyond an experimental methods course, and a lab section. Within a year, she was preparing to transfer, and by April of 1918 she was settling in at the University of Göttingen. Here, she came to the notice of Peter Debye, a future Nobel Prize winner, when she complained to one of his teaching assistants about the low difficulty level of the labs he had assigned, and the poor quality of the equipment allotted for the students’ use. She was told to go to Debye’s office and present her criticisms in person which, amazingly, she did, and even more amazingly, which Debye responded positively to, setting her on a path of independent research which culminated in her writing her dissertation with him.


After only four semesters of study at Gottingen, Sponer took the oral examinations for her PhD in March of 1920. Ordinarily, she would have taken longer to learn more material, but Debye was planning on leaving the university shortly, and in his absence, her examination would have fallen to Robert Pohl, who was notoriously against the higher education of women, and might therefore do his level best to stack the examination against her. Ultimately, she passed her orals with an overall mark of “Very Good.”


Rather than remaining at Göttingen, where the focus was on theoretical physics, Sponer decided to find an institute where she could perfect her experimental technique, and Debye fatefully recommended to her that she go to Berlin and the Kaiser Wilhelm Institute, where Fritz Haber (the Nobel laureate we have met before in the tragic and sinister guise as the husband of Clara Immerwahr) was her supervisor and, more monumentally, where she met a young man named James Franck, thirteen years her senior, who would play a pivotal role in her life for the next four decades.



Before World War I, Franck had become famous for his work in verifying an early quantum prediction about how electrons of certain energies interact with atoms and now, after a brief stint as a soldier in the German army, he was returning to his research. Sponer’s first paper from her time at the Institute was an extension of this work. Sponer and Franck worked well together, and in 1921, when Franck was made the head of an experimental physics institute in Göttingen created by his friend Max Born, he took Sponer along with him as his Assistentin.


A gregarious and inspiring teacher and leader, Franck created a legendary intellectual atmosphere in Göttingen that set aside the rigid formalities of the usual German university system. Here it was that the new quantum physics was applied to the interpretation of atomic and molecular structures, and where the experiments were performed that dramatically supported even the most extreme predictions of the new paradigm.


To begin with, Sponer continued her work in measuring how often electron collisions with atoms induce the electrons in those atoms to undergo a quantum leap. It was not until 1924 that she pushed off into the research that would cement her name in the global physics community, the study of molecular spectra.


So, what is a molecular spectrum? You might remember from your high school chemistry courses that, when a photon of light of a particular frequency is absorbed by a lone atom, it can take that energy and use it to promote one of its electrons to a higher energy level. Since most atoms have many different electrons, there are many different promotions that can take place, each of a very particular energy. Those energies are so specific that, just by looking at the energies absorbed by an atom, or those emitted by one, you can identify what the atom is. An atom’s absorption spectrum, which is a tally of all the different energies absorbed by it, acts for scientists like a tell-tale fingerprint.


When you send photons of energy at something containing more than a single atom, however, the story of what is absorbed and what that energy is used for becomes much more complicated, and molecular spectra in the early 20th century were correspondingly much harder to interpret than atomic spectra. Not only can molecules (consisting of two or more atoms bonded together) use incoming energy to promote electrons to higher energy orbits, but they can also use it to change how their atoms vibrate relative to one another, AND how they rotate around different possible axes. The more atoms there are in a molecule, the more possible vibrational states there will be, and the more asymmetric the molecule is, the more likely it is that the molecule’s rotational states will require distinctly different amounts of energy, all summing to a rich cornucopia of absorbed energies which it was Sponer’s task to untangle.


What Sponer did as a physicist throughout the 1920s, and up through the 1960s, was to take the complicated patterns produced by gaseous molecules exposed to different energies of light, and interpret them employing the theoretical mathematical models emerging from the great modern physics capitals of Berlin, Göttingen, and Copenhagen. This branch of physics, called molecular spectroscopy, was among our most powerful techniques for determining the bond lengths between the different atoms of a molecule, and the angles between them. By knowing what different energies were required to induce different types of rotation, for example, you could determine the moments of inertia around those different axes, and once you know that, coupled with the masses of the atoms involved, you can start mapping out the lengths of all the bonds and thus create geometrical pictures of increasingly complicated molecular structures.


On the strength of her work in molecular spectroscopy, Sponer received her Habilitation in 1925, which brought with it the ability to lecture at the university level. In the 25 years from 1908 to 1933, of the 10,595 women in Germany who obtained their doctorate, only 54 received a Habilitation, less than half of whom went on to become professors. Predictably, Robert Pohl was vehemently against the appointment, but relented when Franck promised that, should he ever leave the university, Sponer would as well.


That seemed an unlikely possibility in that banner year of 1925, however, and soon after receiving her Habilitation, Sponer also received a Rockefeller grant to study at the University of California, Berkeley, for a year, where she wished to learn their highly successful techniques in the field of vacuum ultraviolet spectroscopy. She learned a great deal about science while there (and developed a technique with Raymond Birge for using measured vibrational frequencies to calculate the energy required to break a molecule apart, known today as the Birge-Sponer Method), and the development of her English language skills would prove to be deeply important to her in the lean years ahead, but it was also an unfortunate time to leave Göttingen, as 1925 saw an explosion of quantum mathematical progress there, including Heisenberg’s landmark paper producing a matrix mechanical explanation of electron orbitals and quantum transitions. It was also the year that James Franck won the Nobel Prize for Physics.


The late 1920s were an era of mounting professional respect and international reputation for Sponer, and in 1930 she was commissioned by the prestigious German science publishing house Springer to produce a book on molecular structure. That work would have to wait, however, as in January of 1933 the Nazi party came to power in Germany, and on April 7 promulgated the Law for the Restoration of the Professional Civil Service whereby all Jews serving in universities were to be removed from their positions, with the exception of World War I veterans.


James Franck was half-Jewish, but as a war veteran he could have maintained his position at Göttingen. Courageously, however, he elected to renounce his position in protest of the treatment of Jewish intellectuals in Germany. The decision made Franck a hero of the international intellectual community, but left Sponer in an awkward position. Classified as an Aryan by the Nazi state, she could have kept her position, but with Franck gone, Pohl expected her to leavel in accord with Franck’s 1925 promise.



Even if Pohl had been willing to keep Sponer on at Gottingen, in May of 1933 the German state passed the Law for the Modification of Regulations Concerning Civil Servants, Their Salaries, and Benefits, which restricted women’s ability to advance in their professions and downgraded their pay scale, sending a clear indication of things to come for women at work in government. Sponer saw that her position at Gottingen was fast becoming untenable, and started making plans for emigration, either to Norway or the United States. In 1934, she moved to Oslo, where she would spend the next two years trying to get the University of Oslo on some kind of footing in the world of experimental physics. Though not the dismal situation that Lise Meitner found herself in when she moved to the University of Stockholm in 1938, it was nonetheless soon clear to her that this was not the place to continue her life’s work, and in 1936 she accepted an appointment at Duke University.


At Duke, Sponer had the funding and administrative support she needed to build a new department that married the best of European experimental techniques with the best of American educational principles. As the situation in Germany deteriorated for scientists, she became active in the emigre community organizing resources to bring as many imperilled scientists and their families to the United States as possible, thereby rescuing some of the continent’s greatest minds from the calamities to come. During World War II, she worked in the V-12 Program, training Navy and Marine officer candidates in accelerated education programs, while sporadically continuing her work on the spectroscopy of aromatic compounds (molecules composed of rings of atoms, like benzene).


In 1946, Hertha Sponer married James Franck, who had come to America the year before she had, and had worked on the Manhattan Project during the war on the condition that he would be able to directly advise the government against its actual use should they succeed in building it. His wife of 35 years had died in 1942, and in the ensuing years he sank deeper into ill-health and depression. The marriage of Sponer and Franck in 1946 was a tonic to both, pulling them from their respective loneliness and heartbreak over the state of their home country, and giving them both something to look forward to in the future.


Franck remained at the University of Chicago, while Sponer stayed at Duke, so the newly married pair saw each other primarily during vacations and scientific conferences, which made their time together all the more precious. Franck died in 1964, by which point Sponer was suffering from an Alzheimer’s-like form of dementia which had to be increasingly compensated for by her friends and loyal students. At Franck’s funeral, she was unable to deliver a brief eulogy, and one year later, in 1965, Hertha Sponer retired from Duke University after nearly three decades of service in which she built the experimental physics program up from the ground to become one of the nation’s leading centers of molecular investigation. She was brought back to Germany by her family in 1966, declared incapable of independent self-care in 1967, and died in a sanatorium in Ilten on February 17, 1968.


FURTHER READING:


Marie-Ann Maushart’s 1997 Um nicht zu vergessen: Hertha Sponer - ein Frauenleben fuer die Physik im 20. Jahrhundert was translated in 2011 by Ralph A. Morris and is the source to have for the career of Hertha Sponer, and has a good deal of highly interesting information as well about women’s evolving place in the German university system in the early 20th century.


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