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Abstract
The most sophisticated theoretical studies to date have been conducted on two distinct systems of broad chemical interest. The first is the tert-butyl peroxy radical (ROO.), a species integral to low-temperature (< 900 K) oxidation of branched alkanes (e.g., isobutane) which occurs in engines and the atmosphere. Coupled-cluster energetics have been computed for two reaction systems heavily modulated by ROO.: the addition of O2 to the tert-butyl radical and tert-butyl hydroperoxy radical. In addition, the fundamental vibrational transitions for the X A' and A A' electronic states of ROO. have been predicted using second-order vibrational perturbation theory, and compared to experiment. The second system is the methane-formaldehyde complex (MFC), a candidate for reliable modeling of a C-HO hydrogen bond (HB). Several HB-related properties (geometries, frequencies, orbital interactions, magnetic properties, and electron topology) were quantified for six coupled-cluster optimized structures of the MFC. Comparison of these values to those for the traditional water dimer HB indicates that the lowest energy MFC conformer --- a potential global minimum ignored in previous research --- is clearly bound by a C-HO HB