Data collection, quantum mechanics

Computers are already an important tool of chemistry. Computer-assisted documentation, the collection and evaluation of experimental data, and quantum mechanical calculations of molecular properties predominate. The importance of the solution of chemical problems such as the design of syntheses with the aid of computers is not yet widely recognized, but will have far-reaching consequences and may well lead to rather fundamental changes in the activity of chemists. In... 

Data were collected from students enrolled in three different courses. Class A was a one-semester introductory quantum mechanics course intended for junior physics majors that typically enrolled about 10 students. Class B was the second-half of a two-semester physical chemistry course for chemistry majors that typically enrolls 30-40 students. The first semester of this course focuses primarily on thermodynamics the second-half spends the first two-thirds of the semester on quantum mechanics and then concludes with a discussion of statistical mechanics. Class C is offered every semester for junior-year chemical engineering majors, and was observed three times Cl, C2, and C3. Cl and C3 were offered during the fall semester, when the mainline population of chemical engineering majors take the course and had enrollments of approximately 70 students. C2 was offered in the spring semester and is frequently taken by students who have done a "co-op" or internship in industry, which requires them to be off-campus for a semester at a time. C2 had an enrollment of around 30 students. The material in Class C is quite similar to the material offered in Class B. The first three-quarters of this class covers quantum mechanics, the remaining time is spent on statistical mechanics. 

Scientists are always on the lookout for patterns. When a pattern is observed in the data, it can be stated as a scientific law, a succinct summary of a wide range of observations. For example, one of the earliest laws of chemistry was the law of constant composition, which states that a compound has the same composition regardless of the source of the sample. Thus, a sample of water has twice as many hydrogen atoms as oxygen atoms, no matter where the sample is collected. The laws of quantum mechanics concern the behavior of electrons in atoms. 

Molecular geometries measured with condensed-phase techniques such as X-ray diffraction or NMR cannot be regarded as inherent properties of isolated species. Similarly, as the "determination" of molecular geometries from microwave spectra involves collation of data pertaining to many spectroscopic states of species differing in isotopic compositions, such geometries are merely collections of fitting parameters that cannot be viewed as quantum-mechanical observables. 

Examination of the gas-phase basicities ( AGf) for substituted anilines and pyridines falls closely in line with the familiar patterns found for the response of these systems to electron-demanding reactions in solution. It is comforting to find that the enormous collection of data which has been stored in the various aromatic substituent parameters [22, 23, 24] applies to solvent-free systems and this gives verisimilitude to their interpretation in quantum-mechanical terms such as resonance or bond hybridization. 

In 1976, in Houston, Fry and Thompson used the 7 S-j b P-j 6 Sq cascade in Mercury 200. Their selective excitation involved a C.W. single-line-laser. The signal was several order of magnitude larger than in previous experiments, allowing them to collect the data in a period of 80 minutes. Their result was in excellent agreement with Quantum Mechanics and violated generalized Bell s inequalities by 4 standard deviations. 

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