###### About

Experimental studies of molecular structure. Quantum chemistry. Isotope effects. Kinetics of extremely rapid phase changes. Molecular dynamics studies of recrystallization.

###### Representative Publications

On the thermal expansion of molecules. Z. Varga, M, Hargittai, L. S. Bartell, Structural Chemistry, 22, 111, (2011).

Personal reminiscences about theories used and misused in structural chemistry. L. S. Bartell, Structural Chemistry, 22, 247 (2011).

Molecular Dynamics Simulations of Solid State Recrystalliation I: Observation of Grain Growth in Annealed Iron nanoparticles. Jinfan Huang and L. S. Bartell, J. Solid State Chem. 0185,238-244 (2011).

The Correct Physical Basis of Protobranching Stabilization. L. S Bartell, J. Phys. Chem. A 116, 10460 (2012).

Molecular Dynamics Studies of the Size and Temperature Dependence of the Kinetics of Freezing of Fe Nanoparticles, Bo Zhao, Jinfan Huang, and L. S. Bartell, .l Solid State Chem, in press.

###### Scientific Milestones

1953. Design and construction of an electron diffraction apparatus for gas molecules that yielded molecular structures an order of magnitude more precise than other units at the time produced. Conceived of and explained a vibrational effect later known as "the Bastiansen-Morino shrinkage affect" making, for example, the O-O mean internudlear disatance in the linear molecule CO2 less than twice the C-O mean distance. This claim is confirmed by J. Karle in "Fifty Years of Electron Diffraction."

1955. Because the new experimental data yielded by the 1953 apparatus contained more precise information about molecular structure than could be derived using the crude existing analyses of data, a greatly improved scheme to analyze data was developed. It has subsequently been adopted internationally

1953. The first experimental measurement via electron diffraction of the distribution of planetary electrons around an atom. X-ray diffraction measurements of electron distributions had been made before but, because the x-ray wave lengths were about 20 times longer than the electron wave length, the x-ray resolution was too crude, for example, to resolve the different electron shells in the argon atom. Electron diffraction data resolved those shells.

1956 – 1961. Initiated the first spectroscopic studies of thin films as thin as a partial monolayer, by what has become known as ”ellipsometric spectroscopy,” now a widely applied method (655,000 hits on Google). One virtue is that the spectrum is that of the film, irrespective of the amount of chromophore in the supernatant It was based on the realization that the ellipsometric measurement of thickness of a film was on the optical thickness, not the geometrical thickness, and therefore, measurements as a function of optical wavelength would reveal the anomalous dispersion (in index of refraction) associated with optical absorption maxima.

1960 Introduced a new way, now recognized as the correct way, to understand what determines bond angles in molecules. The interpretation supersedes the previous “hybridization theory,” and even the popular VSEPR theory, and is currently known as “ligand-close-packing.”

1960. Predicted and measured secondary isotope effects on bond-lengths in molecules. The first example was the difference in C-C bond length of H3C-CH3 vs D3C-CD3, .an effect claimed by spectroscopists at Ottawa, to be “impossible!”

1964. Effects of electron correlation in x-ray and electron diffraction intensities. This research formulated the first approach to direct experimental measurements of the spatial distributions of electrons as governed by their mutual repulsions and led to continued studies by many laboratories. At the time, the theoretical treatment of electron correlation was the greatest obstacle to accurate quantum calculations of atomic and molecular structure.

1966. Measured isotope effects on molar volume and surface tension, and introduced a simple theoretical model for hydrocarbons. The standard theory of isotope effects of statistical mechanics was unable to account for such effects, for they turned out to be related to intramolecular anharmonic vibrations, not simple mass related intermolecular interactions.. Biegeleisen, a leading expert on isotope effects, named our explanation the “Bartell-Roskos” effect.

1967 – 1976. Introduced the first formulations of “Molecular Mechanics” force fields explicitly incorporating rational nonbonded interactions including geminal interactions. It made far more accurate predictions of molecular structures than existing formulations of molecular mechanics incorporating a greater number of parameters. This was because our force field was a more faithful representation of the physics of force fields than that used by the (mainly) organic chemists who initiated molecular mechanics studies..

1972. The first computationally practical way of treating interatomic, intramolecular dynamic scattering of electrons. This explained the observed deviations between calculated and experimental electron diffraction patterns in cases where fairly heavy atoms were involved, cases where the existing treatment of molecules with heavy atoms by Shomaker & Glauber, based on intra-atomic dynamical scattering theory, was insufficient

1973. The first molecular orbital treatments of chemisorptions to interpret some experimental observations. Later Nobel Laureate Roald Hoffman asked if I would mind if his group participated in this field of computation.

1974. Atomic and molecular images via electron holography. The first method to apply electron holography to obtain the full resolution afforded by the short electron wavelength. It worked by producing the coherent reference beam needed, by scattering electrons from a site within the sample, itself. This approach was eventually applied, both for electrons and x-rays, by a number of laboratories

1975. Introduced the new method of Predicate Observations in analyses of molecular structure by diffraction or spectroscopic techniques. If standard analyses gave large correlations between parameters (spoiling accurate determinations of the parameters), the method of predicate observations (weighted estimates of certain parameters) could break the correlation and allow much more accurate determinations of structural parameters. The method was quickly adopted by spectroscopists.

1977. Ab initio quantum study of secondary isotope effects on molecular structure. A quantum mechanical verification of a predicted effect originally claimed by spectroscopists to be impossible.

1979. The first quantitative theory of the optical spatial domain filter used to filter out Airy diffraction fringes from molecular images obtained by electron holography.. .

1981. Complementarity in the double-slit experiment. On simple realizable systems for observing intermediate particle-wave behavior. This paper was included in a book which collected key papers on Quantum Measurement Theory (including papers by Einstein, Heisenberg, Bohr and other significant contributors).

1982. Electron diffraction studies of extremely hot molecules. What distinguished this study from many others of hot molecules was the extreme speed with which the heating and probing of the molecules was carried out. This meant that molecules could be probed while they were vibrating so violently that they were on the verge of flying apart. The methods used in previous studies of hot molecules disintegrated the molecules at much lower temperatures because of the long residence times the hot molecules suffered.. What was learned were details of the force fields of molecules that spectroscopy was blind to. It enabled tests to verify the validity of a simple model force field I developed based on the popular VSEPR (or, better, ligand close-packing) theory.

1983. Intermolecular multiple scattering of electrons, the first accurate theory, and experimental test.

1984. The first electron diffraction study of the structure of a liquid (in this case benzene) which turned out to be considerably more discriminating than prior x-ray and neutron diffraction studies - - partly because of the low temperature that was possible with the new technique and partly because of the much shorter wavelength of the electrons..

1987. A new method for analyzing powder diffraction patterns of crystals that successfully solved the crystal structure from powder patterns which had defied prior massive attempts to analyze. The new method provided a way to avoid getting trapped in false minima in least squares analyses, a problem that defeated previous Rietveld analyses..

1989. Electron diffraction studies of rapidly pulsed supersonic cluster beams by rapidly pulsed electron beams. Electromagnetic disturbances in prior techniques for pulsing electron beams had disturbed the electron beams unacceptably. Rapid pulsing made it possible to prevent shock waves from interfering with the probed sample.

1991. Investigation of the kinetics of freezing of liquids by what was said at the time to be the first new method in fifty years - - a method making possible the study of the kinetics of extraordinarily fast phase changes (faster by a factor well over 10-orders of magnitude than afforded by prior methods).

1994. A new procedure based on overlap integrals for identifying materials from their powder patterns (devised in 1977 when I was a consultant for the Mobil Corporation, a corporation which finally allowed the method to be published in 1994 [since the method was so superior to the standard method that Mobil did not initially want to reveal it to its competitors]).

1994. Record supercooling in the laboratory of liquid water to 200 K, and the kinetics of freezing at that temperature.

1996. Isomeric differences in the nucleation rates of crystalline hydrocarbons from their melts.

1998. Theory and observation of effects of capillary waves on shapes of liquid clusters. .

2001. Tolman's delta, surface curvature, compressibility effects, and the free energy of drops (verifying what was wrong with Tolman’s well known expression for how surface tension depends on drop size).

2004. Transient nucleation: Computer Simulations vs. Theoretical Inference. One of the first accurate studies of nucleation in the period during which the nucleation rate climbs from zero to reach a steady state.

2005. How hydrides misled chemists. A paper showing how our diffraction studies undermined the concepts of “hybridization theory,” the “valence force field,” and early so called “’high quality’ quantum chemical computations,” - - and what has replaced those concepts.

2004 – 2006. A new procedure for analyzing nucleation kinetics that, for the first time, reveals the size of critical nuclei.

2007. A refutation of claims that highly supercooled liquids freeze by spinodal decomposition.

2009. Generation of proto-snowflakes in supersonic flow, confirming conjectures that snowflakes start out in a metastable form of ice, not the stable form of the fully grown snowflakes, and revealing the shape and crystalline orientation of the newly formed flakes.

2009. A paper testing the “constrained equilibrium hypothesis” which is incorporated into almost all treatments of nucleation. Our analysis shows how, where, and why the hypothesis fails, and furthermore shows that published proposals for avoiding the use of the hypothesis would also fail, and why.

2011. The first study of recrystallization of metals on an atomic scale. In prior work (none on an atomic scale) the process was referred to as "nucleation," a term that couldn't be strictly true since no new phase is involved. Because our study was on an atomic scale, we could see any "nucleus" involved if there were one (we did not see one) and proposed a different mechanism with the same kinetics.