Theoretical Studies of Au3+/0/- Clusters Using Density Funtional Theory

In this study, the PW91PW91 method with LANL2DZ level was carried out to settle the dispute about the most stable structure of Au3+/0/-. Molecular orbital analyses and Walsh diagram were adopted to rationalize our computational result about the ground state geometry of Au3+/0/-. Our results show that the most stable geometry of Au3 is bent structure (C2v) with bond angle 146.0°. The less stable structure is equilateral triangle structure (D3h) with relative energies of 1.74 eV. The D3h structure possesses multiplicity 4 while the C2v structure 2. In addition, the most stable geometry of Au3+ and Au3- are equilateral triangle structure (D3h) and linear structure (D∞h), respectively. The preference of geometric change can be rationalized simply by using Walsh diagram. Besides, the linear structure of Au3 is found to be transition states (TS) of inversion of B-Au3. The inversion barrier is estimated to be 0.04 eV.

Umbrella inversion and structure of phosphorus-containing compounds: A quantum chemical study

Ab initio and density functional theory calculations were used to determine structure and inversion barrier at phosphorous (III) for open and cyclic phosphorus-containing compounds. Structures of the investigated systems were compared with the available experimental data. Effects of ring size on the P-inversion barriers in these molecules have been discussed. The largest/smallest inversion barrier was reported for phosphocyclopropene/trivinylphosphine (85.1/21.0 kcal/mol). Inversion rate and half-life time were computed.

Slow Preconditioning for the Abrupt Convective Jump over the Northwest Pacific during Summer

The rapid intensification of convective activity in mid-July over the northwest Pacific marks the final stage of the Asian summer monsoon, accompanied by major shifts in regional rainfall and circulation patterns. An entraining plume model is used to investigate the physical processes underlying the abrupt convective jump. Despite little change in sea surface temperature (SST), gradual lower-troposphere mixing leads to a threshold transition in the model as follows. Before mid-July, although SST is already high (29°C), the convective plume is inhibited by the capping inversion above the trade cumulus boundary layer. As the lower troposphere is gradually mixed, the boundary layer top rises with reduced atmospheric stability and increased humidity in the lower troposphere. These factors weaken the inhibition effect of the inversion on the entraining plume. As soon as the plume is able to overcome the inversion barrier, it can rise all the way to the upper troposphere. This marks an abrupt threshold transition to a deep convection regime with heavy rainfall. The convective available potential energy (CAPE) of the entraining plume is found to be a better indicator of the rainfall intensity compared to the conventional undiluted CAPE. The latter fails to capture the onset by neglecting interactions between convective clouds and the environment. Current general circulation models (GCMs) fail to capture the abrupt convective jump and instead simulate a rather smooth seasonal evolution of rainfall. Compared to observations, GCMs simulate a higher trade cumulus top with excessive mixing in the lower troposphere. Convection is no longer inhibited by the inversion barrier, and rainfall simply follows the smooth variation of SST.

Aminophenol isomers unraveled by conformer-specific far-IR action spectroscopy

Far-infrared action spectroscopy of aminophenol in the gas-phase revealed isomer- and conformer-specific vibrational signatures and provided the heights of NH2 inversion barrier.

Synthesis of dinucleoside acylphosphonites by phosphonodiamidite chemistry and investigation of phosphorus epimerization

The reaction of the diamidite, (iPr2N)2PH, with acyl chlorides proceeds with the loss of HCl to give the corresponding acyl diamidites, RC(O)P(N(iPr)2)2 (R = Me (7), Ph (9)), without the intervention of sodium to give a phosphorus anion. The structure of 9 was confirmed by single-crystal X-ray diffraction. The coupling of the diamidites 7 and 9 with 5′-O-DMTr-thymidine was carried out with N-methylimidazolium triflate as the activator to give the monoamidites 3′-O-(P(N(iPr)2)C(O)R)-5′-O-DMTr-thymidine, and further coupling with 3′-O-(tert-butyldimethylsilyl)thymidine was carried out with activation by pyridinium trifluoroacetate/N-methylimidazole. The new dinucleoside acylphosphonites could be further oxidized, hydrolyzed to the H-phosphonates, and sulfurized to give the known mixture of diastereomeric phosphorothioates. The goal of this work was the measurement of the barrier to inversion of the acylphosphonites, which was expected to be low by analogy to the low barrier found in acylphosphines. However, the barrier was found to be high as no epimerization was detected up to 150 °C, and consistent with this, density functional theory calculations give an inversion barrier of over 40 kcal/mol.

COMPARATIVE QUANTUM STUDY ON TERT-BUTYL RADICAL AND CATION

Detailed comparative analysis of properties of the tert-butyl radical and cation is performed using 14 density functional (DFT) methods combined with double-zeta and triple-zeta quality Gaussian basis sets with polarization and diffuse functions. Stability of different conformers is discussed. Structural parameters, dipole moment, adiabatic ionization potential (IP), inversion barrier and isotropic hyperfine coupling constants are examined and compared to values obtained at the standard MP2 level and to experimental data available. All methods indicate that that the CC bond in the radical is longer than in the cation by about 0.033 Å. The IP values are found to be very sensitive to the method used and range from 612 to 709 kJ/mol, but majority oscillate around 646÷656 kJ/mol. Calculated inversion barrier for the radical is higher than the experimental estimate of 2.68 kJ/mol; with the 6-311++G** basis set and most DFT methods it is predicted in the range 3.86÷4.82 kJ/mol. All DFT methods predict for the out-of-plane CC3 bending mode of the radical the frequency around 260 cm-1, while in the cation the corresponding frequency is higher by about 180 cm-1.