Characterization of plasma catalytic decomposition of methane: role of atomic O and reaction mechanism

In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted methane oxidation over a Ni-SiO2/Al2O3 catalyst. We evaluated possible reaction mechanisms by analyzing the correlation of gas phase, surface and plasma-produced species. Plasma feed gas compositions, plasma powers, and catalyst temperatures were varied to expand the experimental parameters. Real-time Fourier-transform infrared spectroscopy (FTIR) was applied to quantify gas phase species from the reactions. The reactive incident fluxes generated by plasma were measured by molecular beam mass spectroscopy (MBMS) using an identical APPJ operating at the same conditions. A strong correlation of the quantified fluxes of plasma-produced atomic oxygen with that of CH4 consumption, and CO and CO2 formation implies that O atoms play an essential role in CH4 oxidation for the investigated conditions. With the integration of APPJ, the apparent activation energy was lowered and a synergistic effect of 30% was observed. We also performed in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) to analyze the catalyst surface. The surface analysis showed that surface CO abundance mirrored the surface coverage of CHn at 25 oC. This suggests that CHn adsorbed on the catalyst surface as an intermediate species that was subsequently transformed into surface CO. We observed very little surface CHn absorbance at 500 oC, while a ten-fold increase of surface CO and stronger CO2 absorption were seen. This indicates that for a nickel catalyst at 500 oC, the dissociation of CH4 to CHn may be the rate-determining step in the plasma-assisted CH4 oxidation for our conditions. We also found the CO vibrational frequency changes from 2143 cm-1 for gas phase CO to 2196 cm-1 for CO on a 25 oC catalyst surface, whereas the frequency of CO on a 500 oC catalyst was 2188 cm-1. The change in CO vibrational frequency may be related to the oxidation of the catalyst.

Elaboration of a Predictive Qsar Model of the Anti-Paludial Activity of a Series of Dihydrothiophenone Molecules at Theory Level B3LYP/ 6-31G (d, p)

The purpose of this study is to develop a QSAR model predictive of the antimalarial activity of a series of Dihydrothiophenone molecules using quantum chemical methods. The molecules were optimized from the B3LYP/6-31G (d, p) level of theory. The extracted descriptors are the vibrational frequency of the carbonyl group (Ѵ(C=O)), enthalpy of formation (Δ f H°), the valence angle between the carbon-nitrogen-carbon atoms α(C-N-C) and the ionization potential (I); The application of the RLM method of the XLSTAT program allowed us to develop a regression model. The statistical indicators (R²=93.50%, S=0.211, F=43.678) of the developed model attest to its robustness and reliability. Internal and external validation parameters (Q2loo et Q2ext) reveal that the established model performs well in predicting the antimalarial activity of the series of molecules studied. It can therefore be used to design new HD molecules belonging to its field of applicability at a 95% confidence level.

Ab initio investigation on the low-lying states of LaX (X = Se, Sn, Sb)

Potential energy curves for the low-lying electronic states of the title molecules in their neutral and anionic forms have been calculated by means of the diffusion Monte Carlo method. The effect of different trial functionals has been investigated using single determinants constructed from density functional theory (DFT) orbitals with B3LYP, B3PW91, and M06-2X functions. Bond length, vibrational frequency, and electron affinity have also been numerically derived for the selected species and the ground state has been assigned. Spectroscopic parameters obtained are interpreted and compared to their isovalents, shedding some light on further investigations on the selected dimers.

Hydrogen Bonds: Raman Spectroscopic Study

The work outlines general ideas on how the frequency and the intensity of proton vibrations of X–H×××Y hydrogen bonding are formed as the bond evolves from weak to maximally strong bonding. For this purpose, the Raman spectra of different chemical compounds with moderate, strong, and extremely strong hydrogen bonds were obtained in the temperature region of 5 K–300 K. The dependence of the proton vibrational frequency is schematically presented as a function of the rigidity of O-H×××O bonding. The problems of proton dynamics on tautomeric O–H···O bonds are considered. A brief description of the N–H···O and C–H···Y hydrogen bonds is given.

Structural dynamic response analysis due to the slit flow between the tailplane and the elevator

Any aircraft in flight is subjected to dynamic loads. Following vibration-related accidents, a flow field and vibration analysis can be carried out to analyze the data and study the cause of the accident. When slit airflow enters the cavity between the tailplane structure and the elevator, a mixed vortex is formed. If the vortex-induced vibrational frequency of around 50 Hz happens to be close to the natural frequency of the structure at 46 Hz, it is likely to induce structural vibration (resonance). The resonance can cause excessive fatigue damage which can ultimately lead to structural failure and the loss of the component or the aircraft. Damping methods can be employed to control vibration within the structure by reducing the amplitude of that vibrational motion by 83%. This article details a recreation of one example of structural vibration within an airborne aircraft.

Molecular structure and spectra of danthron and emodin studied by FTIR, Raman spectroscopy and DFT techniques

In this work, experimental and theoretical studies on danthron and emodin are presented. Experimentally, Fourier transform infrared (FTIR), Raman and UV–Vis spectra of danthron and emodin were recorded. The structure and vibrational frequencies of the molecules were calculated using density functional theory (DFT) with the B3LYP functional using the triple zeta (TZVP) basis set. Among various possible structures of danthron and emodin, it was found that the most stable structures involve intramolecular hydrogen bonds between two OH and C=O groups. The theoretical IR spectra of the most stable conformations of danthron and emodin correlate well with their experimental FTIR. Detailed vibrational frequency analysis was done for all the vibrational modes obtained and were assigned to the ring vibrations along with the stretching and bending of specific bond vibrations. The bands obtained from the experimental FTIR and Raman spectra of both the molecules correlate well with their theoretical data.