Phosphine polymerization by nitric oxide: experimental characterization and theoretical predictions of mechanism.

A yellow solid material [P(x)H(y)] has been obtained in the reaction of phosphine (PH(3)) and nitric oxide (NO) at room temperature and characterized by thermogravimetric analysis mass spectrometry (TGA-MS) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. In this work using complete basis set (CBS-QB3) methods a plausible mechanism has been investigated for phosphine polymerization in the presence of nitric oxide (NO). Theoretical explorations with the ab initio method suggest (a) instead of the monomer the nitric oxide dimer acts as an initial oxidant, (b) the resulting phosphine oxides (H(3)P=O <--> H(3)P(+)O(-)) in the gas phase draw each other via strong dipolar interactions between the P-O groups, and (c) consequently an autocatalyzed polymerization occurs among the phosphine oxides, forming P-P chemical bonds and losing water.

Extended Hückel tight-binding approach to electronic excitations.

In this work, we propose the application of a self-consistent extended Huckel tight-binding (EHTB) method in the computation of the absorption optical spectrum of molecules within the linear response time dependent density functional formalism. The EHTB approach is presented as an approximation to the Kohn-Sham energy functional. The method is applied to the computation of excitation energies and oscillator strengths of benzene, pyridine, naphthalene, diazines, and the fullerenes: C(60)(I(h)), C(70)(D(5h)), and C(80)(D(2)).

Dependence of Spurious Charge-Transfer Excited States on Orbital Exchange in TDDFT: Large Molecules and Clusters.

Time-dependent density functional theory (TDDFT) is a powerful tool allowing for accurate description of excited states in many nanoscale molecular systems; however, its application to large molecules may be plagued with difficulties that are not immediately obvious from previous experiences of applying TDDFT to small molecules. In TDDFT, the appearance of spurious charge-transfer states below the first optical excited state is shown to have significant effects on the predicted absorption and emission spectra of several donor-acceptor substituted molecules. The same problem affects the predictions of electronic spectra of molecular aggregates formed from weakly interacting chromophores.

N-nitrosation of amines by NO2 and NO: a theoretical study.

Gas-phase nitrosation of amines implies a nonionic pathway different from the nitrosonium nitrosation via acidification of nitrite. Electronic structure calculations discussed in this work suggest a free radical mechanism, in which NO2 abstracts a hydrogen atom from the nitrogen in primary and secondary amines to form an intermediate complex of an aminyl radical and nitrous acid. The aminyl radical intermediate is then quenched by nitric oxide, leading to the formation of nitrosamine.

Chemisorption-induced spin symmetry breaking in gold clusters and the onset of paramagnetism in capped gold nanoparticles.

We present a simple model to describe the induction of magnetic behavior on gold clusters upon chemisorption of one organic molecule with different chemical linkers. In particular, we address the problem of stability of the lowest lying singlet and show that for some linkers there exists a spin symmetry-breaking that lowers the energy and leads to preferential spin density localization on the gold atoms neighboring the chemisorption site. The model is basically an adaptation of the Stoner model for itinerant electron ferromagnetism to finite clusters and it may have important implications for our understanding of surface magnetism in larger nanosystems and its relevance to electronic transport in electrode-molecule interfaces.