Full geometry optimizations have been performed at the MP2 level of theory using the 6-31G(d,p) basis set for the five common nucleic acid bases (uracil, thymine, cytosine, adenine, and guanine) and three related bases (fluorouracil, 5-methylcytosine, and hypoxanthine). Several electric properties were subsequently calculated using the optimized geometries and the larger polarized basis sets of Sadlej. Including electron correlation decreases the magnitude of the dipole moments by 10-15% for every base except adenine. In all cases, inclusion of electron correlation increases the mean polarizability by 8-12% and also increases the polarizability anisotropy by as much as 14-20%. Results for structurally similar bases were compared in order to qualitatively study the effects of functional group substitution on geometries and electric properties.

Thin films of solid ammonia (NH(3) and ND(3)) have been characterized using low temperature (25-110 K) Fourier-transform infrared (FTIR) spectroscopy, and the three solid phase (amorphous, metastable, and crystalline) spectra are reported. This work has been motivated by confusion in the literature about the metastable and crystalline phases as a result of an early erroneous report by Staats and Morgan [(J. Chem. Phys. 31, 553 (1959)]. Although the crystalline phase has subsequently been reported correctly, the metastable phase has not been described in the literature in detail. The unique characteristics of the metastable phase, reported here for the first time, include multiple peaks in the nu(2) and nu(3) regions and peak intensities that are dependent on the deposition temperature. This behavior may be the result of (a) preferential molecular orientations in the solid, or (b) exciton splitting due to different crystal shapes in the solid. The amorphous and metastable phases of deuterated ammonia are also reported for the first time.

The three-dimensional ground state potential energy surfaces for He–Cl2, Ne–Cl2, and Ar–Cl2 have been calculated using the single and double excitation coupled-cluster approach with noniterative perturbational treatment of triple excitations [CCSD(T)]. Calculations have been performed with the augmented correlation consistent triple zeta basis sets supplemented with an additional set of bond functions. Single point calculations for approximate minima have also been performed with several other basis sets including the quadruple zeta basis set (aug-cc-pVQZ) with bond functions. For He–Cl2 and Ar–Cl2 the CCSD(T) results show that the linear configuration is lower in energy than the T-shaped one. For Ne–Cl2 the CCSD(T) approach predicts the T-shaped configuration to be lower in energy. The linear configuration has been found to be more sensitive than the T-shaped one to the changes of the Cl–Cl bond length with the interaction becoming weaker when the Cl–Cl bond length is shortened from its equilibrium value and stronger when it is lengthened. More detailed analysis shows that sensitivity of component energies such as exchange, dispersion, and induction is much greater than that of supermolecule results. The interaction in the T-shaped configuration becomes slightly stronger for shorter Cl–Cl bonds. For He–Cl2 and Ar–Cl2 the larger zero-point vibrational energy of the linear configuration is responsible for making the T-shaped configuration the ground vibrational state. Vibrational effects further increase the difference in energy between the ground state T-shaped configuration of Ne–Cl2 and its linear counterpart.

The infrared spectra of solid hydrogen sulfide (H2S) and deuterium sulfide (D2S) were collected at very low temperatures. Vapor deposition of thin films at the lowest temperature of 10 K produced amorphous solids while deposition at 70 K yielded the crystalline phase III. Infrared interference fringe patterns produced by the films during deposition were used to determine the film thickness. Careful measurement of the integrated absorbance peaks, along with the film thickness, allowed determination of the integrated band intensities. This report represents the first complete presentation of the infrared spectra of the amorphous solids. Observations of peaks near 3.915 and 1.982 microm (ca. 2554 and 5045 cm(-1), respectively) may be helpful in the conclusive identification of solid hydrogen sulfide on the surface of Io, a moon of Jupiter.

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