Einar Lindholm
As a graduate student Einar Lindholm started his scientific career in Stockholm with studies of the optical spectra of diatomic molecules in the laboratory of Professor Erik Hulthen, in those days the leader of the famous Swedish school of band spectroscopy. Lindholm made careful measurements and analysed the results with the available theories of diatomic molecules to find their vibrational and rotational energy levels. But, already at this initial stage of his career, Einar Lindholm was not satisfied with accurate experiments, he also wanted to penetrate deeper into the theory behind the observations. Thus, his doctoral thesis (1942) also included an investigation of the pressure broadening of atomic spectral lines by foreign gases. Earlier theories were only valid within narrow limits, either for low pressures and in the core of the line or for very high pressures, so that comparisons with experiments scarcely were possible. Lindholm then developed a theory of general validity which included the earlier theories as special cases and allowed a theoretical computation of the whole line contour, both in the core and in the distant parts of the wings, and for any pressure of the foreign gas. His theory was successfully compared both with his own measurements (Hg atoms in argon) and with other measurements, already available in literature.
In those days, it was very difficult to make an academic career in Sweden. Except for occasional teaching with very modest salary the only university positions available were the few ones as full professor. Einar Lindholm therefore spent some years in industrial laboratories and as a high school teacher. But after World War I1 the climate changed, and around 1950 some positions as assistant or associate professor were created. Einar Lindholm was then appointed associate professor in Gothenburg, and later, in 1956, full professor at the Royal Institute of Technology in Stockholm.
By the mid-1940s Lindholm had already become interested in mass spectrometers and designed a spectrometer for isotope analysis in biology, mainly for light elements such as carbon, nitrogen or oxygen. For routine work of this kind only low resolving power was necessary. In Gothenburg he continued to construct mass spectrometers, but now for analysis of collisions between molecules and slow positive ions. In this context it turned out to be necessary to work simultaneously with two mass spectrometers of high accuracy.
In 1953 Einar Lindholm constructed the first tandem mass spectrometer. This instrument had an electrostatic lens system of his own construction for the production of a durable beam of particles with very low kinetic energy (down to 0.5 eV). In the beginning, the ion beam disappeared after 20 to 30 minutes. This annoying problem was solved by Lindholm through covering the electrodes with a thin graphite layer, thus eliminating the surface charge.
Einar Lindholm's pioneering work on tandem mass spectrometers was very successful. Today there are hundreds of this type of instrument all over the world, mainly used for chemical analysis but also for basic research.
Lindholm and his co-workers used the tandem mass spectrometers to investigate molecular ionization processes and ion-molecule reactions with