The Baltimore-Washington Infant Study is a regional epidemiologic study of congenital heart disease. Among Infants born in the study area in 1981 and 1982, 664 had a diagnosis of congenital heart disease confirmed in the first year of life by echocardiography, cardiac catheterization, cardiac surgery, or autopsy. The prevalence rate was 3.7/1,000 livebirths for all cases and 2.4/1,000 livebirths for cases confirmed by invasive methods only. Diagnosis-specific prevalence rates of congenital heart disease are compared with those of eight previous case series. Changing diagnostic categorizations in the time span covered and methodological differences resulted in great variation of the data. However, the data of the New England Infant Cardiac Program which used the same case discovery methods showed similar occurrences of major morphologic abnormalities, suggesting that these are stable basic estimates in the eastern United States. For all case series, the rate of confirmed congenital heart disease was approximately 4/1,000 livebirths over the 40-year time span.

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Infrared and ultraviolet spectra of the gauche and anti conformers of matrix-isolated permethyl-n-tetrasilane have been obtained separately by taking advantage of thermally induced gauche-to-anti conversion and of wavelength-selective photochemical destruction of either conformer. The resolved UV spectrum of the gauche conformer provides the first piece of experimental evidence in favor of the recently proposed reinterpretation of conformational effects on tetrasilane electronic states. According to this, it is not the energy but the intensity of the lowest singlet excitation that changes dramatically as the SiSiSiSi dihedral angle is varied, as a result of an avoided crossing between s̀s̀* and s̀π* states. Implications for the general understanding of sigma conjugation in simple terms are discussed. Unconstrained MP2/6-31 G* optimization predicts the existence of a third backbone conformer (ortho), with a dihedral angle of about 90°. Its predicted (HF/3-21 G*) mid-IR spectrum is indistinguishable from that of the gauche conformer, and the matrix-isolation spectra thus provide no evidence for or against its presence.

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Geometries of A4X10 molecules (A = C, Si; X = H, F, Cl, Br, CH3, SiH3) have been optimized at the HF/6-31G* level as a function of the AAAA dihedral angle ω. In addition to the generally known gauche and trans conformational minima, some have an additional (“ortho”) minimum near ω = 90°. This appears only within a certain critical range of sizes of substituents X. It is attributed to a splitting of the ordinary gauche minimum by 1,4 interactions between substituents, similarly as the twisting of the anti minimum from 180° is attributable to 1,3 interactions. A universal model is proposed to rationalize the appearance and subsequent disappearance of the ortho minimum as X increases in size. It contains intrinsic barriers described according to Weinhold, van der Waals interactions described by a Lennard-Jones 6−12 potential, and Coulomb charge−charge interactions.