The products of the reaction of Sc and dioxygen have been reinvestigated. By adding the electron-trapping molecule CCl4, additional information about the IR spectra has been obtained, as well as the observation of new bands. New ab initio calculations are also performed on possible products of the Sc plus O2 reaction. The previously observed band at 722.5 cm-1 is assigned as the b2 mode of ScO2 -. Bands arising from ScO+, Sc(O2)+, and(O2)ScO are also assigned. We are still unable to assign any bands to OScO. The problems associated with the computational study of ScO2 are discussed.

Laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm−1 due to (NO)2+, a new absorption at 1221.0 cm−1, and a band set at 1300.3, 1222.7, 884.4 cm−1. The latter bands decrease more on annealing than the 1221.0 cm−1 band. Isotopic substitution (14NO,15NO, 15N18O, and mixtures) shows that these new vibrations involve two equivalent N–O oscillators, which identifies two new (NO)2 species. The excellent agreement with frequencies, intensities, and isotopic frequency ratios from density functional theory calculations substantiates assignment of the 1221.0 cm−1 band to trans-(NO)2− and the three band set to cis-(NO)2−. The observation of a weak combination band at 2492.0 cm−1 further substantiates assignment of the two N–O stretching modes in cis-(NO)2−.

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Experiments and ab initio calculations have been performed to study the catalytic activity of calcium oxide and magnesium oxide toward N 2 O decomposition. The experiments were carried out in a fixed-bed quartz reactor in the temperature range 773-1223 K. The decomposition of N 2 O appeared to be a first-order reaction with activation energies of 26 kcal/mol for CaO and 36 kcal/mol for MgO, respectively. The decomposition rate did not change when excess oxygen was introduced to the inlet gas. The ab initio energy barriers of the dissociative reaction:-, in which the oxygen anion is seated in a CaO(100) or MgO(100) model surface, are 22 and 33 kcal/mol. High-temperature preexponential factors and activation energies are estimated from transition-state theory and collision theory expressions. The values agree well with those obtained experimentally. This indicates that most of the surface anions of both CaO and MgO are active in decomposing N 2 O in the temperature range investigated. A model of a plug-flow reactor is used to demonstrate that the temperature dependence of the overall reaction rate obtained at high N 2 O concentrations reflects the regenerating process of the surface and not the molecular dissociation of N 2 O.

The full-potential linearized augmented plane wave method has been employed to determine electronic density of states, 1s core level shifts, and total 1s core ionization energies for the isoelectronic compounds graphite, diamond, C 3 N 4 , and graphitic C 11 N 4 . The C 3 N 4 crystal structures studied are the graphitic, ␣, ␤, cubic, and pseudocubic configurations. All the C sp 3 bonded structures have band gaps 0.5-1.5 eV smaller than that of diamond. Only the C 3 N 4 composition of the C sp 2 phases has a band gap. The core level shifts and ionization energies are compared with x-ray photoelectron energies. The 1s energies of C atoms connected to zero, one, two, and three N in C 11 N 4 are close to experimental XPS shifts and peak positions. Nearly all the N 1s energies are within the experimental nitrogen XPS energy range. The C 1s ionization energies of the tetrahedral carbon C 3 N 4 phases are between 288.6-289.5 eV, which is 4.0-4.9 eV higher than the C 1s value of pure graphite. ␤-C 3 N 4 has the highest value. This compound has two N 1s ionization energies at approximately 400.0 and 400.6 eV. ͓S0163-1829͑99͒14239-5͔