Origin of Anomalous Electronic Circular Dichroism Spectrum of RuPt₂(tppz)₂Cl₂(PF₆)₄ in Acetonitrile

We report a theoretical study of the structures, energetics, and electronic spectra of the Pt^II/Ru^II mixed-metal complex RuPt₂(tppz)₂Cl₂(PF₆)₄ (tppz = 2,3,5,6-tetra­(2-pyridyl)­pyrazine) in acetonitrile. The hybrid B3LYP density functional theory and its TDDFT methods were used with a complete basis set (CBS) extrapolation scheme and a conductor polarizable continuum model (C-PCM) for solvation effects. Results showed that the trinuclear complex has four types of stable conformers and/or enantiomers. They are separated by high barriers owing to the repulsive H/H geometrical constraints in tppz. A strong entropy effect was found for the dissociation of RuPt₂(tppz)₂Cl₂(PF₆)_n in acetonitrile. The UV–visible and emission spectra of the complex were also simulated. They are in good agreement with experiments. In this work we have largely focused on exploring the origin of anomalous electronic circular dichroism (ECD) spectra of the RuPt₂(tppz)₂Cl₂(PF₆)₄ complex in acetonitrile. As a result, a new mechanism has been proposed together with a clear illustration by using a physical model

Exploring the Ring-Opening Pathways in the Reaction of Morpholinyl Radicals with Oxygen Molecule

Quantum chemistry calculations using hybrid density functional theory and the coupled-cluster method have been performed to investigate the ring-opening pathways in the oxidation of morpholine (1-oxa-4-aza-cyclohexane). Hydrogen abstraction can form two different carbon-centered radicals, morpholin-2-yl or morpholin-3-yl, or the nitrogen-centered radical, morpholin-4-yl, none of which are found to have low-energy pathways to ring-opening. Extensive exploration of multiple reaction pathways following molecular oxygen addition to these three radicals revealed two competitive low energy pathways to ring-opening. Addition of O₂ to either carbon-centered radical, followed by a 1,4-H shifting mechanism can yield a long-lived cyclic epoxy intermediate, susceptible to ring-opening, following further radical attack. In particular, the second pathway begins with O₂ attack on morpholin-2-yl, followed by a 1,5-H shift and a unimolecular ring-opening without having to overcome a high barrier, releasing a significant amount of heat in the overall ring-opening reaction. The calculations provide valuable context for the development of mechanisms for the low temperature combustion chemistry of nitrogen and oxygen-containing fuels

Full-Dimensional Quantum Calculations of Vibrational Levels of NH₄⁺ and Isotopomers on An Accurate Ab Initio Potential Energy Surface

Vibrational energy levels of the ammonium cation (NH₄⁺) and its deuterated isotopomers are calculated using a numerically exact kinetic energy operator on a recently developed nine-dimensional permutation invariant semiglobal potential energy surface fitted to a large number of high-level ab initio points. Like CH₄, the vibrational levels of NH₄⁺ and ND₄⁺ exhibit a polyad structure, characterized by a collective quantum number <i>P</i> = 2­(<i>v</i>₁ + <i>v</i>₃) + <i>v</i>₂ + <i>v</i>₄. The low-lying vibrational levels of all isotopomers are assigned and the agreement with available experimental data is better than 1 cm^–1

Doppler-Resolved Kinetics of Saturation Recovery

Frequency-modulated laser transient absorption has been used to monitor the ground-state rotational energy-transfer rates of CN radicals in a double-resonance, depletion recovery experiment. When a pulsed laser is used to burn a hole in the equilibrium ground-state population of one rotational state without velocity selection, the population recovery rate is found to depend strongly on the Doppler detuning of a narrow-band probe laser. Similar effects should be apparent for any relaxation rate process that competes effectively with velocity randomization. Alternative methods of extracting thermal rate constants in the presence of these non-thermal conditions are evaluated. Total recovery rate constants, analogous to total removal rate constants in an experiment preparing a single initial rotational level, are in good agreement with quantum scattering calculations, but are slower than previously reported experiments and show qualitatively different rotational state dependence between Ar and He collision partners. Quasi-classical trajectory studies confirm that the differing rotational state dependence is primarily a kinematic effect