PROFESSOR EMERITUS(P)

B.S. Oregon State University, 1943

Ph D. California Institute of Technology, 1948

Although formally retired, Professor Hedberg maintains an active research program in physical chemistry. His interests are in the area of molecular structure and intramolecular dynamics.

A knowledge or concept of the structures of molecules is central to the interpretation of chemical results, and it is unusual to find a scientific article in chemistry that does not draw on spatial models of molecules that display or suggest the atoms, bonds, and bond angles. Professor Hedberg's work is concerned with the accurate measurement of molecular structures and with the accurate measurement of molecular structures and with the interpretation of these measurements. The measurements are obtained by the analysis of electron-diffraction patterns that are generated when a fine beam of electrons intersects a jet of gas. Analysis of the patterns with the help of digital computers, often aided by additional data from spectroscopy and quantum-mechanical calculations, leads to a spectrum of interatomic distances such as that shown in the figure for the molecule buckminster-fullerene. These distances allow one to construct a model of the structure and the widths of the corresponding peaks can be interpreted to deduce properties related to intramolecular motion. The technique of electron diffraction (ED) is the most powerful available for studying the structures of gas molecules, and the apparatus at OSU is one of the only few in the world.

There are several kinds of interesting problems. One is simply the structure itself: new, unusual molecules are sometimes put together in unusual ways that may be quickly measured by ED. Another is vibrational force fields: the amplitudes of vibration reflected in the widths of the distance peaks may be interpreted to give values for the force constants of the molecule. A third is conformational analysis: many gas molecules exist as an equilibrium mixture of rotamers, say anti and gauche forms, the proportions of which may be changed by changing the mixture temperature. ED yields the mixture composition as well as the structures of the components and allows one to determine the energy and entropy differences of the components. Chemical properties that may be gotten from these measurements are strengths of internal hydrogen bonds, shapes of torsional potentials, and the heights of barriers hindering internal rotation. Lastly, it is possible to study the structures of materials that are normally regarded to be involatile. Although ED is a technique applied to gases, the vapor pressure required is very small. Sufficient sample from involatile inorganic compounds can very often be had simply by heating them to high temperatures. There are fascinating chemical problems connected with the structures of such materials as gases, and Hedberg's group has constructed ovens that produce gas jets of these to enable the preparation of diffraction patterns from them. .

PROFESSOR EMERITUS(P)

B.S. Oregon State University, 1943

Ph D. California Institute of Technology, 1948

Although formally retired, Professor Hedberg maintains an active research program in physical chemistry. His interests are in the area of molecular structure and intramolecular dynamics.

A knowledge or concept of the structures of molecules is central to the interpretation of chemical results, and it is unusual to find a scientific article in chemistry that does not draw on spatial models of molecules that display or suggest the atoms, bonds, and bond angles. Professor Hedberg's work is concerned with the accurate measurement of molecular structures and with the accurate measurement of molecular structures and with the interpretation of these measurements. The measurements are obtained by the analysis of electron-diffraction patterns that are generated when a fine beam of electrons intersects a jet of gas. Analysis of the patterns with the help of digital computers, often aided by additional data from spectroscopy and quantum-mechanical calculations, leads to a spectrum of interatomic distances such as that shown in the figure for the molecule buckminster-fullerene. These distances allow one to construct a model of the structure and the widths of the corresponding peaks can be interpreted to deduce properties related to intramolecular motion. The technique of electron diffraction (ED) is the most powerful available for studying the structures of gas molecules, and the apparatus at OSU is one of the only few in the world.

There are several kinds of interesting problems. One is simply the structure itself: new, unusual molecules are sometimes put together in unusual ways that may be quickly measured by ED. Another is vibrational force fields: the amplitudes of vibration reflected in the widths of the distance peaks may be interpreted to give values for the force constants of the molecule. A third is conformational analysis: many gas molecules exist as an equilibrium mixture of rotamers, say anti and gauche forms, the proportions of which may be changed by changing the mixture temperature. ED yields the mixture composition as well as the structures of the components and allows one to determine the energy and entropy differences of the components. Chemical properties that may be gotten from these measurements are strengths of internal hydrogen bonds, shapes of torsional potentials, and the heights of barriers hindering internal rotation. Lastly, it is possible to study the structures of materials that are normally regarded to be involatile. Although ED is a technique applied to gases, the vapor pressure required is very small. Sufficient sample from involatile inorganic compounds can very often be had simply by heating them to high temperatures. There are fascinating chemical problems connected with the structures of such materials as gases, and Hedberg's group has constructed ovens that produce gas jets of these to enable the preparation of diffraction patterns from them. .