Systematic analysis of electronic barrier heights and widths for concerted proton transfer in cyclic hydrogen bonded clusters: (HF), (HCl) and (HO) where = 3, 4, 5.

The MP2 and CCSD(T) methods are paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF), (HCl) and (HO) where = 3-5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harmonic vibrational frequencies confirm the nature of each minimum and TS. Both conventional and explicitly correlated CCSD(T) computations are employed to assess the electronic dissociation energies and barrier heights for CPT near the complete basis (CBS) limit for all 9 clusters.

Leaf temperature impacts canopy water use efficiency independent of changes in leaf level water use efficiency.

Canopy water use efficiency (above-ground biomass over lifetime water loss, WUE) can influence yield in wheat and other crops. Breeding for WUE is difficult because it is influenced by many component traits. For example, intrinsic water use efficiency (WUE), the ratio of net carbon assimilation (A) over stomatal conductance, contributes to WUE and can be estimated from carbon isotope discrimination (Δ).

Communication: Gas phase vibrational spectroscopy of the azide-water complex.

The vibrational spectra of the azide-water complex, N (HO), and its fully deuterated isotopologue are studied using infrared photodissociation (IRPD) spectroscopy (800-3800 cm) and high-level computations. The IRPD spectrum of the H-tagged complex exhibits four fundamental transitions at 3705, 3084, 2003, and 1660 cm, which are assigned to the free OH stretching, the hydrogen-bonded O-H stretching, the antisymmetric N stretching, and the water bending mode, respectively. The IRPD spectrum is consistent with a planar, singly hydrogen-bonded structure according to an MP2 and CCSD(T) anharmonic analysis via generalized second-order vibrational perturbation theory.

Dissociation Energy of the HO···HF Dimer.

Even though (HO) and (HF) are arguably the most thoroughly characterized prototypes for hydrogen bonding, their heterogeneous analogue HO···HF has received relatively little attention. Here we report that the experimental dissociation energy ( D) of this important paradigm for heterogeneous hydrogen bonding is too large by 2 kcal mol or 30% relative to our computed value of 6.3 kcal mol.

A Reaction Valley Investigation of the Cycloaddition of 1,3-Dipoles with the Dipolarophiles Ethene and Acetylene: Solution of a Mechanistic Puzzle.

The reaction mechanism of the cycloaddition of 10 1,3-dipoles with the two dipolarphiles ethene and acetylene is investigated and compared using the Unified Reaction Valley Approach in a new form, which is based on a dual-level strategy, an accurate description of the reaction valley far out into the van der Waals region, and a comparative analysis of the electronic properties of the reaction complex. A detailed one-to-one comparison of 20 different 1,3-dipolar cycloadditions is performed, and unknown mechanistic features are revealed. There are significant differences in the reaction mechanisms for the two dipolarophiles that result from the van der Waals complex formation in the entrance channel of the cycloadditions.