Study on the kinetics and dynamics of the H2 + NH2- reaction on a high-level ab initio potential energy surface.

Gas-phase ion-molecule reactions play major roles in many fields of chemistry and physics. The reaction of an amino radical anion with a hydrogen molecule is one of the simplest proton transfer reactions involving anions. A globally accurate full-dimensional potential energy surface (PES) for the NH2- + H2 reaction is developed by the fundamental invariant-neural network method, resulting in a root mean square error of 0.116 kcal mol-1. Quasi-classical trajectory calculations are then carried out on the newly developed PES to give integral cross sections, differential cross sections and thermal rate coefficients. This reaction has two reaction channels, proton transfer and hydrogen exchange. The reactivity of the proton transfer channel is about one or two orders of magnitude stronger than that of the hydrogen exchange channel in the energy range studied. Vibrational excitation of H2 promotes the proton transfer reaction, while fundamental excitation of each vibrational mode of NH2- has a negligible effect. In addition, the theoretical rate coefficients of the proton transfer reaction on the PES show inverse temperature dependence from 150 to 750 K, in accordance with the available experimental results.

Dissociative photodetachment of H3O2-: a full-dimensional quantum dynamics study.

The transition state is a central concept of chemistry. Photoelectron-photofragment coincidence (PPC) spectroscopy has been proven as an attractive method to study the transition state dynamics. Within a state-of-the-art full-dimensional quantum mechanical model, the dissociative photodetachment dynamics of H3O2- is investigated on accurate anion and neutral potential energy surfaces. The calculated PPC spectrum of H3O2- agrees well with the experimental measurement. The dissociative product OH is exclusively populated on the ground vibrational state, implying the character of the spectator bond. In contrast, the product H2O is predominantly populated in the ground and fundamental states of the symmetric and antisymmetric stretching modes, which is caused by the strong coupling between the antisymmetric motion of the transferred H atom in the transient intermediate [H3O2]* and both stretching modes of the product H2O.

Mode- and Bond-Selected Reaction of H with Local Mode Molecule HDS.

Understanding mode- and bond-selected dynamics of elementary chemical reactions is of central importance in molecular reaction dynamics. The initial state-selected time-dependent wave packet method is employed to study the mode and bond selectivity, isotopic branching ratio, and temperature dependence of rate constants of the two-channel reaction of H with local mode molecule HDS. For the abstraction channel, fundamental excitation of the HS (DS) bond of the reactant HDS significantly enhances the H-abstraction (D-abstraction) reaction, whose efficacy is higher than the same amount of translational energy except at low energies just above the energy threshold. This is in sharp contrast to the prediction of Polanyi rules: translational energy is more efficient than vibrational energy in enhancing a reaction with an early barrier. The recent sudden vector projection model is then applied to rationalize the observed mode specificity, which, however, shows that the translational mode vector has a larger coupling with the reaction coordinate than the stretching vector of the active bond, implying a reversed relative efficacy on promoting the reaction as well. In contrast, the mode and bond specificity for the exchange channel is not as strong as for the abstraction channel due to the regulation of the shallow well along the reaction path.

Pituitary Prolactinoma Imaged by 99mTc-Sestamibi SPECT/CT in a Multiple Endocrine Neoplasia Type 1 Patient.

A 35-year-old woman who had undergone bilateral inferior parathyroidectomy for primary hyperparathyroidism was referred to our hospital to evaluate the cause of irregular menses, galactorrhea, and paroxysmal headache. Multiple endocrine neoplasia type 1 was then suspected for the high levels of plasma prolactin, parathyroid hormone, serum calcium, insulin, and related symptoms. A Tc-sestamibi SPECT/CT acquired to evaluate parathyroid glands unexpectedly revealed an increased accumulation in the pituitary gland, which was further confirmed by enhanced magnetic resonance imaging as a pituitary microadenoma. Bromocriptine treatment gradually reduced the prolactin level.