Potential energy curves for neutral and multiply charged carbon monoxide

Potential energy curves of various electronic states of CO ⁿ⁺ (0 ≤ n ≤ 6) are generated at MRCI/CASSCF level using cc-pvQZ basis set and the results are compared with available experimental and theoretical data.     

Blue shift in X-H stretching frequency of molecules due to confinement

The effect of spatial confinement on the properties of isoelectronic molecules HF, H2O, NH3, and CH4 has been studied by encapsulating them in a C60 fullerene cage. Second-order M?ller-Plesset perturbation theoretical (MP2) calculations suggest that all the guest species are stable inside the fullerene cage. This stabilization arises from the dispersion interaction between the guest and the host. It is shown that the excitation energy (Esigma*-Esigma) for the X-H bond increases and that there is a blue shift in the stretching frequencies due to confinement.     

Isotopic branching in (He, HD+) collisions

A three-dimensional time-dependent quantum mechanical approach is used to calculate the reaction probability (P(R)) and the integral reaction cross section (sigma(R)) for both channels of the reaction He + HD+(v = 0, 1, 2, 3; j = 0) --> HeH(D)+ + D(H), over a range of translational energy (E(trans)) on two different ab initio potential energy surfaces (McLaughlin-Thompson-Joseph-Sathyamurthy and Palmieri et al.). The reaction probability plots as a function of translational energy exhibit several oscillations, which are characteristic of the system. The vibrational enhancement of the reaction probability and the integral reaction cross section values are reproduced qualitatively by our calculations, in accordance with the experimental results. The isotopic branching ratio for the reaction decreases in going from v = 0 to v = 1 and then becomes nearly v-independent in going from v = 1 to v =3 on both the surfaces.     

Beta-phenyl quenching of triplet excited ketones: how critical is the geometry for deactivation?

The phenomenon of beta-phenyl quenching has been examined by laser-flash photolysis in a series of alpha- and/or beta-substituted ketones 4-8 with similar excited-state characteristics. It is found that alpha-substitution markedly increases the triplet lifetimes in contrast to beta-substitution. The force field calculations for the various staggered conformers of ketones 4-6 and 8-syn show that the lowest-energy conformation in all these ketones has the carbonyl group and the beta-phenyl ring gauche to each other. Despite this geometrical requirement, the longer lifetimes observed are interpreted as being due to the influence of the alpha-substituent on the rotational freedom of the planar benzoyl moiety as a whole. The experimental results are suggestive of the attainment of what appears to be a critical geometry for quenching. This scenario may be likened to Norrish type II reactions, where the alpha-substituent has long been known to suppress the elimination pathway and promote Yang cyclization. In addition, we have shown that the diastereomers of alpha,beta-disubstituted ketones exhibit distinct lifetimes.     

Hydrogen bonding without borders: an atoms-in-molecules perspective

It is shown that the electron density at the hydrogen bond critical point increases approximately linearly with increasing stabilization energy in going from weak hydrogen bonds to moderate and strong hydrogen bonds, thus serving as an indicator of the nature and gradual change of strength of the hydrogen bond for a large number of test intermolecular complexes.     

Solvation of H3O+ by phenol: hydrogen bonding vs pi complexation

Ab initio calculations at the second-order M?ller-Plesset perturbation theoretic level have been carried out to study the solvation of protonated water by phenol molecules. The results show that in addition to classical O-H...O hydrogen bonds, C-H...O, pi...H-O, and pi...H-C bonds are also formed, thus stabilizing the H3O+(C(6)H(5)OH)3 complex.     

Advanced development of TFA-MOD coated conductors

American Superconductor is manufacturing 2G wire for initial commercial applications. The 2G wire properties satisfy the requirements for these initial projects; however, improvements in the critical current, field performance and cost are required to address the broad range of potential commercial and military applications. In order to meet the anticipated the performance and cost requirements, AMSC’s R&D effort is focused on two major areas: (1) higher critical current and (2) enhanced flux pinning.AMSC’s current 2G production wire, designed around a 0.8 μm thick YBCO layer deposited by a Metal Organic Deposition (MOD) process, carries a critical current in the range of 200–300 A/cm-w (77 K, sf). Achieving higher critical current requires increasing the thickness of the YBCO layer. This paper describes recent progress at AMSC on increasing the critical current of MOD-YBCO films using processes compatible with low-cost, high-rate manufacturing.     

Location of energy barriers. VIII. Reagent → product energy conversion on surfaces with sudden or gradual late-barriers

At energies well above the threshold for reaction, the effect of additional reagent vibration (ΔV′) and relative translation (ΔT′) on the product energy distribution (V,R,T,) has been examined on four different substantially endothermic potential-energy surfaces for two extreme mass combinations (LH + H $\text{endo}$ L + HH and HH + L $\text{endo}$ H + HL). As noted previously, additional reagent vibration tends to be retained as product vibration, ΔV′ → ΔV, and a similar approximate adiabaticity applies to translation, ΔT′ → ΔT + ΔR. The present work is concerned with the effect of potential-energy surface and extreme mass-combination on these generalizations. The surfaces examined had late barrier-crests, but surfaces designated S exhibited a sudden rise to the barrier-crest and G a gradual rise. The extent of adiabaticity was found to be significantly greater on the gradual (G-type) surfaces than on the sudden (S-type) ones. The mass-combination LH + H $\text{endo}$ L + HH (in which enhanced reagent orbital angular momentum correlates with enhanced product rotation) was anomalous in giving ΔT′ → ΔR.     

Time-dependent density functional theoretical study of the absorption properties of BN-substituted C60 fullerenes

Time-dependent density functional theoretical calculations using the B3LYP functional and 6-31G* basis set for a series of BN-substituted C60 fullerenes reveal that, unlike C60, these molecules would absorb in the visible region and that the optical and electronic properties of fullerenes can be fine-tuned with proper BN substitution.     

An experimental and theoretical investigation of the photophysics of 1-hydroxy-2-naphthoic acid

Photophysical and photochemical properties of 1-hydroxy-2-naphthoic acid (1,2-HNA) have been investigated experimentally by steady state and time domain fluorescence measurements and theoretically by Hartree-Fock (HF), configuration interaction at the single excitation (CIS) level, density functional theoretic (DFT), and semiempirical (AM1) methods. 1,2-HNA exhibits normal fluorescence that depends on its concentration, nature of the solvent, pH, temperature, and wavelength of excitation. It seems to form different emitting species in different media, akin to 3-hydroxy-2-naphthoic acid (3,2-HNA). The large Stokes shifted emission observed at pH 13 is attributed to species undergoing excited-state intramolecular proton transfer. Nonradiative transition seems to increase on protonation and decrease on deprotonation. AM1(PECI=8) calculations predict the absorption maximum (lambda(max) = 335.9 nm) in reasonable agreement with experiment (lambda(max) = 352 nm) for the neutral 1,2-HNA. They also predict a red shift in absorption on protonation and a blue shift on deprotonation as observed experimentally. CIS calculations tend to overestimate the energy gap and hence underestimate the absorption maxima between the ground and the excited electronic states of 1,2-HNA and its protonated and deprotonated forms. However, they do predict correctly that the excited state intramolecular proton transfer is likely to occur in the deprotonated form of 1,2-HNA and not in the neutral and the protonated forms. A single minimum is found in the potential energy profile for the ground state as well as the first excited state of 1,2-HNA and its protonated species. In contrast, a double minimum with a nominal barrier in between is predicted for the ground state and also the first three excited states of the deprotonated species. The keto form of the deprotonated species is found to be slightly less stable than the enol form in all the states investigated.