Theoretical study on adsorption and dissociation of NO2 molecule on Fe(111) surface.

We applied periodic density-functional theory (DFT) to investigate the adsorption and dissociation of NO(2) on a Fe(111) surface. The most favorable adsorption configuration of NO(2)/Fe(111) is the FeNO(2)(S-mu(3)-N,O,O') configuration with NO(2) at the 3-fold-shallow site of the surface, which has an adsorption energy -64.59 kcal/mol. Of two geometries of NO(2)/Fe(111) for the stepwise NO(2) deoxygenation, one is the most stable structure, FeNO(2)(S-mu(3)-N,O,O'), with activation barriers 10.38 and 19.36 kcal/mol to break the first (ON-O bond activation) and second (N-O bond activation) nitrogen-oxygen bonds, respectively; another configuration FeNO(2)(B-mu(2)-N,O) has a smaller energy barrier (3.88 kcal/mol) to break the first ON-O bond. All these findings show that NO(2) can readily decompose on the Fe(111) surface. The rate constants for the two aforementioned processes were also predicted by VTST and RRKM theory, and the predicted total rate constants, k(total) (in units of cm(3) molecule(-1) s(-1)), can be represented by the equations k(total) = 5.61 x 10(-5)T(-2.060) exp(-0.639 kcal mol(-1)/RT) at T = 100-1000 K. To acquire insight into the great catalytic activity of the Fe(111) surface for the decomposition of NO(2), the nature of the interaction between the adsorbate and the substrate is subjected to a detailed electronic analysis.

Theoretical study on reaction mechanisms and kinetics of cyanomidyl radical with NO.

The mechanisms and kinetics of the reaction of the cyanomidyl radical (HNCN) with the NO have been investigated by the high-level ab initio molecular orbital method in conjunction with VTST and RRKM theory. The species involved have been optimized at the B3LYP/6-311++G(3df,2p) level and their single-point energies are refined by the CCSD(T)/aug-cc-PVQZ//B3LYP/6-311++G(3df,2p) method. Our calculated results indicate that the favorable pathways for the formation of several isomers of an HNCN-NO complex. Formations of HNC + N(2)O (P1) and HNCO + N(2) (P2) are also possible, although these two pathways involve little activation energy. Employing the Fukui functions and HSAB theory, we are able to rationalize the scenario of the calculated outcome. The predicted total rate constants, k(total), at a 760 Torr Ar pressure can be represented by the equations k(total) = 4.39 x 10(8) T(-7.30) exp(-1.76 kcal mol(-1)/RT) at T = 298-1000 K and 1.01 x 10(-32) T(5.32) exp(11.27 kcal mol(-1)/RT) at T = 1050-3000 K, respectively, in units of cm(3) molecule(-1) s(-1). In addition, the rate constants for key individual product channels are provided in a table for different temperature and pressure conditions. These results are recommended for combustion modeling applications.