Fifty Years of Gas-Phase Electron-Diffraction Structure Research: A Personal Retrospective

Abstract

The author has spent nearly five decades working on the molecular structure of gaseous molecules using principally the method of electron diffraction. During this time he has seen and participated in the development of the method from its crude beginning in which the diffraction patterns were measured by hand and interpreted by eye, to the powerful, nearly automatic instrument-based methods of today. Accompanying this evolution in the method is a similar evolution in the complexity of the scientific problems. Whereas in the early days the molecules studied were necessarily simple and the parameter determinations accurate to a few hundredths of anÅngström, electron diffraction today is routinely applied to molecules with a 10-fold greater numbers of parameters and yields results 10 times more accurate. This article summarizes some of the many recollections accumulated by the author during that professional journey.

Quasistructural molecules

“…It must be added that there are many structures other than the "equilibrium" one defined in the literature. 6,13 The large number of temperature-dependent, rovibrationally averaged structures (position (r z , r α,T ) and distance (angle) averages (r g,T , r a,T ), as well as mass-dependent (r m ) and empirical (r 0 , r s ) ones), 6,13,[22][23][24] though they correspond much more closely to what one might call "measured" structures, are not considered in this review, as they are also based on the BO approximation when computed and thus they do not enhance the present discussion.…”

Crystallography in Structural Chemistry

“…At this point, it is proper to stress that the term crystallography has become synonymous with the science of structure; thus, it embraces structural studies in gases and liquids as well. The development of the gas-electron-diffraction technique has also received exposure in our periodical Structural Chemistry [12,13]. Beside gases, the electron diffraction technique has also been used extensively for the analysis of solid structures.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 16, 2005) and the discipline

“…In the next article, Hedberg [49] gives an account of his experience with gas-phase electron diffraction throughout the duration of his involvement with this area of research.…”