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The molecular structure and vibrational spectrum of N,N-dimethylformamide have been investigated by ab initio Hartree-Fock, MP2, and density functional theory BLYP and B3LYP methods in conjunction with basis sets ranging from 6-31G* to 6-311+G(2d,p). At all levels of theory, the heavy atom skeleton is found to be planar. The calculated CH 3 -N-CH 3 and N-CO-H bond angles significantly differ from the results of a recent electron diffraction study, but are in reasonable agreement with early lower level theoretical results. Comparison between the calculated and electron diffraction structural parameters of many simple amides indicates that the theoretical methods employed in the present study are reliable for describing the structural features of amides. Thus, the significant difference between the recent electron diffraction structural parameters and the early theoretical results is not due to basis set incompleteness as suggested by the electron diffraction study. The calculated vibrational spectral features are in good agreement with available experimental results. On the basis of agreement between the calculated and experimental results, assignments of fundamental vibrational modes were discussed and some reassignments were proposed.

Density functional theory and ab initio MP2 6-31G* calculations were carried out to investigate the structures and vibrational spectra of 3,4- and 2,3-pyridyne. It is found that the structure of 3,4-pyridyne is consistent with a formal CC triple bond moiety, but the structure of 2,3-pyridyne is more properly described as having a unit. On the basis of the calculated results, detailed assignments of the observed IR bands of 3,4-pyridyne are proposed. The calculations predict the most prominent IR feature of 2,3-pyridyne is a very strong band around 1826 cm-1, suggesting the search for direct experimental evidence of 2,3-pyridyne should pay attention to this spectral region.

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& CONCLUSIONS This paper presents and evaluates an approach to designing accelerated life testing (ALT) experiments. We believe that knowing the design limits of the test item is critical to successful ALT. Unfortunately, effective methods do not exist for analytically predicting the design limits of most electronic items; therefore, the basis of our approach is a destructive evaluation performed on a small number of test items to measure their design limits. Once the design limits have been established, environmental stress levels can be tailored to achieve the objectives of the accelerated life test, which may include optimizing it for greater acceleration, accuracy, and/or statistical confidence. The approach is oriented toward ALT of electronic systems using multiple stresses and is most applicable to low-cost, high-volume production items. We have evaluated our approach by applying it to a commercial off-the-shelf (COTS) single-board computer (SBC). Results from this application demonstrate that the approach can be quite effective for designing successful ALT experiments.

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