No abstract

No abstract

A complete understanding of the synthesis of urea, (NH2),C0, from NH3, C02, and H20 remains an unsolved problem. It is considered that the formation of the intermediate ammonium carbamate (or the equivalent carbamic acid) takes place through the interaction of neutral species, and that this part of the synthesis is open to ab initio computations. Such calculations are reported on the formation of carbamic acid from NH3, C02, and HzO. We have also investigated the formation of carbonic acid from C02 and H20 showing that the six-membered ring transition state is non-planar, in contradiction with earlier reported calculations.

No abstract

Density functional theory (DFT) calculations on SNS, S 2 N 2 , and S 4 N 2 are reported. Both local and gradientcorrected nonlocal density functionals are used with moderate and large basis sets. The relative energies, structural parameters, and vibrational frequencies are reported for each molecule and compared with the experimental and theoretical data available in the literature. For S 2 N 2 , DFT results predicted the order of stability of the three low-energy structures as linear chain < pairwise ring < alternate ring in contrast to the MP2 results but in agreement with MRCI results. For S 4 N 2 the order of stability is found to be (1,3) isomer < twisted form of (1,4) isomer < chair form of (1,4) isomer. We discuss identification of experimentally observed infrared absorption peaks of S 2 N 2 and S 4 N 2 .