UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses

The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump — XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C—I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.

Numerical Investigation of Shallow Liquid Sloshing in a Baffled Tank and the Associated Damping Effect by BM-MPS Method

Understanding the damping mechanism of baffles is helpful to make more reasonable use of them in suppressing liquid sloshing. In this study, the damping effect and mechanism of vertical baffles in shallow liquid sloshing under a rotational excitation are investigated by an improved particle method. By incorporation of a background mesh scheme and a modified pressure gradient model, the accuracy of impact pressure during sloshing is significantly enhanced. Combined with the advantages of the particle method, the present numerical method is a wonderful tool for the investigation of liquid sloshing issues. Through the analysis of impact pressure, the influences of baffle height and baffle position on the damping mechanism are discussed. The results show that the damping effect of vertical baffles increases with the increase of the elevation of baffle top and decreases with the increase of the elevation of the baffle bottom. Moreover, the resonance characteristics of sloshing are altered when static water is divided into two parts by the vertical baffle. The dominant damping mechanism of vertical baffles depends on the configurations.

Quasi-Classical Trajectory Study of the CN + NH3 Reaction Based on a Global Potential Energy Surface

Based on a combination of valence-bond and molecular mechanics functions which were fitted to high-level ab initio calculations, we constructed an analytical full-dimensional potential energy surface, named PES-2020, for the hydrogen abstraction title reaction for the first time. This surface is symmetrical with respect to the permutation of the three hydrogens in ammonia, it presents numerical gradients and it improves the description presented by previous theoretical studies. In order to analyze its quality and accuracy, stringent tests were performed, exhaustive kinetics and dynamics studies were carried out using quasi-classical trajectory calculations, and the results were compared with the available experimental evidence. Firstly, the properties (geometry, vibrational frequency and energy) of all stationary points were found to reasonably reproduce the ab initio information used as input; due to the complicated topology with deep wells in the entrance and exit channels and a “submerged” transition state, the description of the intermediate complexes was poorer, although it was adequate to reasonably simulate the kinetics and dynamics of the title reaction. Secondly, in the kinetics study, the rate constants simulated the experimental data in the wide temperature range of 25–700 K, improving the description presented by previous theoretical studies. In addition, while previous studies failed in the description of the kinetic isotope effects, our results reproduced the experimental information. Finally, in the dynamics study, we analyzed the role of the vibrational and rotational excitation of the CN(v,j) reactant and product angular scattering distribution. We found that vibrational excitation by one quantum slightly increased reactivity, thus reproducing the only experimental measurement, while rotational excitation strongly decreased reactivity. The scattering distribution presented a forward-backward shape, associated with the presence of deep wells along the reaction path. These last two findings await experimental confirmation.

ExoMol line lists – XLI. High-temperature molecular line lists for the alkali metal hydroxides KOH and NaOH

Potassium hydroxide (KOH) and sodium hydroxide (NaOH) are expected to occur in the atmospheres of hot rocky super-Earth exoplanets but a lack of spectroscopic data is hampering their potential detection. Using robust first-principles methodologies, comprehensive molecular line lists for KOH and NaOH that are applicable for temperatures up to T = 3500 K are presented. The KOH OYT4 line list covers the 0 – 6000 cm−1 (wavelengths λ > 1.67 μm) range and comprises 38 billion transitions between 7.3 million energy levels with rotational excitation up to J = 255. The NaOH OYT5 line list covers the 0 – 9000 cm−1 (wavelengths λ > 1.11 μm) range and contains almost 50 billion lines involving 7.9 million molecular states with rotational excitation up to J = 206. The OYT4 and OYT5 line lists are available from the ExoMol database at www.exomol.com and should greatly aid the study of hot rocky exoplanets.

Rotational excitation of C2H− anion in collision with H2

The discovery of anions in the interstellar medium has shown that they are very reactive species.