The hyperthermal dynamics and kinetics of the title reaction, which plays an important role in hypersonic chemistry for atmospheric entry vehicles, are investigated using quasi-classical trajectory ...methods on a recently developed ground electronic state potential energy surface. The dynamics calculations indicated that the reaction follows a complex-forming mechanism, despite its large endoergicity. The calculated differential cross section is forward–backward symmetric, consistent with a long-lived reaction intermediate supported by the NCN potential well. The lifetime of the reaction complex is sufficiently long that the vibrational distribution of the CN product can be predicted by the phase space theory. The calculated vibrational state specific and thermal rate coefficients follow the Arrhenius behavior, and the agreement with existing low-temperature experimental thermal rate coefficients is satisfactory. Extrapolations to high temperatures relevant to hypersonic conditions are provided.
Reactions involving C and N play an essential role in the chemistry around the surface of a hypersonic spacecraft during its atmospheric re-entry. The collision of CN with other molecules and atoms ...has particular interest in aerothermodynamic modeling. This work focuses on the study of the CN + N → N2 + C reaction in the triplet manifold 3A″ of CN2. A high-level full-dimensional potential energy surface for this system is developed from ab initio calculations at the MRCI-F12 + Q level of theory. This surface is employed in quasiclassical trajectory calculations, and thermal rate coefficients from 100 to 20,000 K are computed. The rates for the formation of N2 are compared with the available experimental data, and good agreement is found. At low and intermediate temperatures, the N2 formation is more efficient than the N-exchange process, while at high temperatures, the rates for both processes are comparable. Finally, analytically modified Arrhenius expressions for the reaction rates of N2 formation and N-exchange are reported.
The HOC+ molecule has for long been detected in several regions of the interstellar medium (ISM). The collisional ro-vibrational rate coefficients of this molecule with the most common colliders in ...the ISM are then required for applying nonlocal thermal equilibrium models. However, this molecule has a low bending frequency (249 cm–1), and the use of the rigid rotor approximation is therefore limited to low collision energies. Also, the complete determination of the ro-vibrational rate coefficients of HOC+ in collision with He requires including the bending motion in the analytical model of the potential energy surface (PES) of the system. The first goal of this work is then to develop the first rigid bender four-dimensional PES for the interaction between HOC+ and He. To this aim, a large grid of ab initio energies are computed at the CCSD(T)-F12b/aug-cc-pVQZ level of theory and an analytical representation of the PES is obtained using a combination of least square and reproducing kernel Hilbert space procedures. The global minimum of this PES is found to be reached for a linear configuration of the complex. In the second part of this study, rigid rotor close-coupling calculations are performed at low collision energy, and the calculated rate coefficients are compared to those previously determined for the collisions of He with its HCO+ isomer.
A systematic study for the rational design of porphyrins (P4 spider-shaped derivatives) with potential application in dye-sensitized solar cells is presented. Using density functional theory (DFT) ...(B3LYP/6-31G*) and time-dependent DFT (M06/6-31G*) we show that the UV-vis absorption properties of a spider-shaped Zn(ii) porphyrin, previously synthesized by Stangel et al., may be greatly improved by applying some push–pull strategies in meso positions. We found that the selected triphenylamine push group induces a remarkable improvement in the absorption bands of P4 spider-shaped derivatives. The pull effect reached through the π-electron-rich phenyl group and the benzodithiazole (BTD) group allowed the Q bands to be red-shifted up to 689 nm, much longer than the 593 nm reported experimentally for the original spider-shaped porphyrin. The adsorption results of the P4 spider-shaped derivatives onto a TiO2-anatase surface model Ti16O34H4 through the carboxylic acid group showed that the adsorptions energies were favourable and very similar in all cases. Natural bond orbitals (NBO) indicated a two-center bond (BD) O(carboxyl)–Ti(TiO2) for the porphyrin with the highest adsorption energy (8.27 kcal mol−1), and donor acceptor interactions from LP O(carboxyl) to Ti(TiO2) for the other porphyrins. The natural transition orbitals (NTO) for P4-derivatives-TiO2 confirm the nature of the excited states associated with Q and Soret bands. Finally, the frontier molecular orbitals revealed charge-separated states between those occupied and unoccupied, indicating a favourable charge-transfer process between the dyes and the surface conduction bands. In conclusion, this work showed a systematic study based on the push–pull strategy that improves the performance of porphyrins with the purpose to be used in dye-sensitized solar cells.
Raikoke, a small, unmonitored volcano in the Kuril Islands, erupted in June 2019. We integrate data from satellites (including Sentinel-2, TROPOMI, MODIS, Himawari-8), the International Monitoring ...System (IMS) infrasound network, and global lightning detection network (GLD360) with information from local authorities and social media to retrospectively characterize the eruptive sequence and improve understanding of the pre-, syn- and post- eruptive behavior. We observe six infrasound pulses beginning on 21 June at 17:49:55 UTC as well as the main Plinian phase on 21 June at 22:29 UTC. Each pulse is tracked in space and time using lightning and satellite imagery as the plumes drift eastward. Post-eruption visible satellite imagery shows expansion of the island's surface area, an increase in crater size, and a possibly-linked algal bloom south of the island. We use thermal satellite imagery and plume modeling to estimate plume height at 10–12 km asl and 1.5–2 × 106 kg/s mass eruption rate. Remote infrasound data provide insight into syn-eruptive changes in eruption intensity. Our analysis illustrates the value of interdisciplinary analyses of remote data to illuminate eruptive processes. However, our inability to identify deformation, pre-eruptive outgassing, and thermal signals, which may reflect the relatively short duration (~12 h) of the eruption and minimal land area around the volcano and/or the character of closed-system eruptions, highlights current limitations in the application of remote sensing for eruption detection and characterization.
•Multidisciplinary characterization of the June 2019 VEI 4 eruption of Raikoke volcano using remote observational data.•Lightning, infrasound, and plume observations correlatively document the three phases of the eruption.•Satellite remote sensing indicates an increase in the island size, crater diameter, and large SO2 injection.•Precursory unrest was not detected with any remote sensing technologies.
Although the magnetic and transport properties of molecular junction systems composed of metalled porphyrins or phthalocyanines have been broadly studied in recent years, to date no studies have been ...devoted to evaluate the aforementioned properties in junction systems featuring metalled expanded porphyrins as active elements. The present work reports a detailed theoretical study of the magnetic and electronic transport properties of the recently synthesized dinuclear Cu(
ii
)-naphthoisoamethyrin complex (PyCu
2
). This is the first work on performing these kinds of studies using a magnetically coupled metallic expanded porphyrin as a molecular kernel. DFT and wave function-based methods have been used to determine the nature of the magnetic interaction between the metallic centres, characterized by the exchange coupling constant
J
, showing that although this was found to be weakly antiferromagnetic, after an exhaustive analysis it turns out that the coupling has a ferromagnetic nature with a value of
J
= 14.2 cm
−1
. Once the magnetic ground state of PyCu
2
was rigorously established, the spin resolved transport properties of the device composed of the expanded porphyrin attached to two gold nano-wires were studied by means of the combination of DFT and the nonequilibrium Green's function formalism, in order to explore PyCu
2
prospects as a possible spintronic device.
The Spin-filter transport properties of a magnetically coupled, binuclear Cu(
ii
) expanded porphyrin based molecular junction, were studied at different bias and gate voltage values, through the DFT-NEGF methodology.
In the last decade, lead triiodide perovskite (APbI
3
) (A: organic cation) solar cells (PSCs) have been broadly studied due to their promising features related to the low cost, easy manufacturing ...process, and stability. Strategies to improve the device stability include the application of techniques such as compositional engineering of the cation of these halide perovskites, but it is still a complex task to find the right balance between the stability and power conversion efficiency of materials and complete devices. In this work, we performed a combined study of five samples of 5-AVA
(1−
x
)
MA
x
PbI
3
(5-AVA: ammonium valeric acid and MA: methylammonium) with
x
= 1.0, 0.75, 0.5, 0.25 and 0.0, using X-ray diffraction (XRD) and UV-VIS spectroscopy measurements in combination with periodic density functional theory (DFT) based calculations. Our samples showed an optical bandgap of 1.58 eV and the coexistence of the two phases as observed by XRD analyses. The theoretical results of the bandgaps for the no mixed phases (
x
= 1.0 and
x
= 0.0) show good agreement with the experiment, obtaining bandgap values overestimated by 0.18 eV and 0.33 eV, respectively. A direct relation between the number of 5-AVA ions in the samples and the stability of the phases was theoretically found and proved through the increment observed in the bandgap and the cohesive energy. We proposed a compositional strategy for perovskites 5-AVA
(1−
x
)
MA
x
PbI
3
with
x
values of at most 0.5, based on the small blue-shift and the low absorbance reduction of the spectrum curve, added to the small phase stabilization found.
In the last decade, lead triiodide perovskite (APbI
3
) (A: organic cation) solar cells (PSCs) have been broadly studied due to their promising features related to the low cost, easy manufacturing process, and stability.
Retrospective eruption characterization is valuable for advancing our understanding of volcanic systems and evaluating our observational capabilities, especially with remote technologies (defined ...here as a space-borne system or non-local, ground-based instrumentation which include regional and remote infrasound sensors). In June 2019, the open-system Ulawun volcano, Papua New Guinea, produced a VEI 4 eruption. We combined data from satellites (including Sentinel-2, TROPOMI, MODIS, Himawari-8), the International Monitoring System infrasound network, and GLD360 globally detected lightning with information from the local authorities and social media to characterize the pre-, syn- and post-eruptive behaviour. The Rabaul Volcano Observatory recorded ~24 h of seismicity and detected SO2 emissions ~16 h before the visually-documented start of the Plinian phase on 26 June at 04:20 UTC. Infrasound and SO2 detections suggest the eruption started during the night on 24 June 2019 at 10:39 UTC ~38 h before ash detections with a gas-dominated jetting phase. Local reports and infrasound detections show that the second phase of the eruption started on 25 June 19:28 UTC with ~6 h of jetting. The first detected lightning occurred on 26 June 00:14 UTC, and ash emissions were first detected by Himawari-8 at 01:00 UTC. Post-eruptive satellite imagery indicates new flow deposits to the south and north of the edifice and ash fall to the west and southwest. In particular, regional infrasound data provided novel insight into eruption onset and syn-eruptive changes in intensity. We conclude that, while remote observations are sufficient for detection and tracking of syn-eruptive changes, key challenges in data latency, acquisition, and synthesis must be addressed to improve future near-real-time characterization of eruptions at minimally-monitored or unmonitored volcanoes.
•Multidisciplinary characterization of the June 2019 VEI 4 eruption of Ulawun volcano using remote observational data.•Infrasound and SO2 capture the initial, ash-poor phase of the eruption.•Lightning and plume observations correlatively document the presence of ash.•Satellite remote sensing indicates ash deposits to the west, flows to the NNW and SE, and an increase in the crater diameter.•Precursory unrest was not detected with any remote sensing technologies.
An accurate determination of the abundances of metal-containing molecules in the interstellar medium or circumstellar gas requires knowledge of molecular data, including the collisional rate ...coefficients. This work is focused on the study of the collision of the aluminum isocyanide (AlNC) molecule, as well as its isomer AlCN, with para-H2 (j = 0). For the AlNC + H2 and AlCN + H2 complexes, averaged potential energy surfaces are developed from ab initio energies computed at the coupled cluster with the single, double, and perturbative triple excitation level of theory. Such surfaces are used in close-coupling calculations. The rate coefficients at low temperature are compared with those for the collisions with He. The use of the mass scaling procedure is a good approximation in the case of AlCN. However, for the collision with AlNC, a different propensity rule is found between the rates with He and para-H2 (j = 0). Finally, rotational rate coefficients for the lowest 26 rotational levels of both molecules, AlCN and AlNC, by collision with para-H2 (j = 0) are reported.
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