Search

This paper reports correlated product distributions for dissociation of the van der Waals complexes NO-CH 4 and NO-N 2 on their A ̃ state surfaces, providing detailed data sets against which calculations can be benchmarked. NO-CH 4 dissociation strongly favors small changes in the CH 4 angular momentum, with Δ J = 0 and 1 providing the bulk of the products. Conversely, the associated NO products show little constraint in terms of the rotational angular momentum transfer, with the full range of energetically accessible angular momentum states populated, although the distributions show minima. The lack of angular momentum transfer to methane accompanied by broad, structured, angular momentum transfer to NO gives the NO-CH 4 dissociation some qualitative similarities to NO-Rg complex dissociation. In contrast, for NO-N 2 , the cluster of highest probability products corresponds to high N 2 angular momentum and low NO angular momentum, with a sharp drop in the probability for populating the highest energetically accessible J states. For both the NO and N 2 products, there appears to be a constraint limiting angular momentum transfer at the highest energetically accessible rotational states. Both complexes show product distributions that include a component attributed to excitation from warm complexes, which provides insight into their internal energies. Interestingly, for NO-N 2 , the 44,475 cm -1 photolysis translational energy release distribution for N = 8 extends to energies beyond those accessible from the highest bound X ̃ states. This indicates either that there are long-lived (>100 μs) states above the X ̃ state binding energy or that there is another mechanism that also contributes to this distribution.

Inverse vulcanization provides dynamic and responsive materials made from elemental sulfur and unsaturated cross-linkers. These polymers have been used in a variety of applications such as energy storage, infrared optics, repairable materials, environmental remediation, and precision fertilizers. In spite of these advances, there is a need for methods to recycle and reprocess these polymers. In this study, polymers prepared by inverse vulcanization are shown to undergo reactive compression molding. In this process, the reactive interfaces of sulfur polymers are brought into contact by mechanical compression. Upon heating these molds at relatively low temperatures (≈100 °C), chemical bonding occurs at the polymer interfaces by S-S metathesis. This method of processing is distinct from previous studies on inverse vulcanization because the polymers examined in this study do not form a liquid phase when heated. Neither compression nor heating alone was sufficient to mold these polymers into new architectures, so this is a new concept in the manipulation of sulfur polymers. Additionally, high-level ab initio calculations revealed that the weakest S-S bond in organic polysulfides decreases linearly in strength from a sulfur rank of 2 to 4, but then remains constant at about 100 kJ mol -1 for higher sulfur rank. This is critical information in engineering these polymers for S-S metathesis. Guided by this insight, polymer repair, recycling, and repurposing into new composites was demonstrated., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report results of a two dimensional laser induced fluorescence study of torsional states, low frequency vibrations, and combinations of torsion with low frequency vibration in m-fluorotoluene up to 560 cm -1 in S 0 and 350 cm -1 in S 1 . Evidence is presented for interactions between torsion and low frequency vibrations in both S 0 and S 1 , demonstrating that the coupling of torsion and vibration observed previously in toluene and p-fluorotoluene extends to a molecule with a threefold torsional barrier. This barrier is low in S 0 (20 cm -1 ) and modest in S 1 (116 cm -1 ). The methyl torsion-vibration interaction is much larger for the mode involving out-of-plane wagging of the methyl group with respect to the planar frame compared with the analogous out-of-plane fluorine atom motion. Methyl group out-of-plane modes were found to be most important for torsion-vibration interactions in toluene and p-fluorotoluene, and the evidence is accumulating that this motion is fundamental in torsion-vibration interactions. Fits of the experimental band positions yield torsion-vibration coupling constants, torsional potential terms (V 3 and V 6 ), and rotational constants (F) for the methyl torsion in S 0 and S 1 . The inclusion of torsion-vibration coupling primarily affects V 6 and F: |V 6 | is reduced and F increased, as was seen previously for the G 12 molecules, toluene and p-fluorotoluene. The torsional barrier height does not appear to influence the magnitude of the torsion-vibration interaction: the coupling constants for the out-of-plane CH 3 wag mode are almost the same in S 0 and S 1 (15.5 cm -1 and 14.0 cm -1 , respectively).

Mercury pollution threatens the environment and human health across the globe. This neurotoxic substance is encountered in artisanal gold mining, coal combustion, oil and gas refining, waste incineration, chloralkali plant operation, metallurgy, and areas of agriculture in which mercury-rich fungicides are used. Thousands of tonnes of mercury are emitted annually through these activities. With the Minamata Convention on Mercury entering force this year, increasing regulation of mercury pollution is imminent. It is therefore critical to provide inexpensive and scalable mercury sorbents. The research herein addresses this need by introducing low-cost mercury sorbents made solely from sulfur and unsaturated cooking oils. A porous version of the polymer was prepared by simply synthesising the polymer in the presence of a sodium chloride porogen. The resulting material is a rubber that captures liquid mercury metal, mercury vapour, inorganic mercury bound to organic matter, and highly toxic alkylmercury compounds. Mercury removal from air, water and soil was demonstrated. Because sulfur is a by-product of petroleum refining and spent cooking oils from the food industry are suitable starting materials, these mercury-capturing polymers can be synthesised entirely from waste and supplied on multi-kilogram scales. This study is therefore an advance in waste valorisation and environmental chemistry., (© 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

We report a two dimensional, laser induced fluorescence study of the lowest 345 cm(-1) region of S0 toluene. Methyl rotor levels of 00 up to m = 6 and of 201 up to m = 4 are observed. The rotor levels of 00 and 201 have quite different energy spacings that are well fit by a model that includes strong torsion-vibration coupling between them. The model requires that the rotor barrier height be revised from -4.84 cm(-1) (methyl hydrogens in a staggered conformation) to +1.57 cm(-1) (eclipsed conformation). However, the 3a2″ state lies below the 3a1″ state as expected for a staggered conformation due to energy shifts associated with the torsion-vibration coupling. It is shown that the rotor wave-functions exhibit little localization at the torsional energy minima. The variation in the m = 0 wavefunction probability distribution with torsional angle is shown to be very similar for the previously accepted negative V6 value and the torsion-vibration coupling model as this coupling shifts the phase of the wavefunction by 30° compared with its phase for V6 alone. The presence of a strong Δυ = ± 1 torsion-vibration coupling involving the lowest frequency vibrational mode provides a potential pathway for rapid intramolecular vibrational energy redistribution at higher energies.

The experimental and theoretical adiabatic ionization energies (IEs) of the rhodium-holmium bimetallic clusters RhHo(2)O(n) (n=0-2) have been determined using photoionization efficiency spectroscopy and density functional theory (DFT) calculations. Both sets of data show the IE of RhHo(2)O to be significantly lower than the values for RhHo(2) and RhHo(2)O(2), which are found to be similar. This indicates that there are significant changes in electronic properties upon sequential addition of oxygen atoms to RhHo(2). The DFT investigations show that the lowest energy neutral structures are a C(2v) triangle for RhHo(2), a C(2v) planar structure for RhHo(2)O where the O atom is doubly bridged to the Ho-Ho bond, and a C(2v) nonplanar structure for RhHo(2)O(2), where the O(2) is dissociative and each O atom is doubly bridged to the Ho-Ho bond in the cluster above and below the RhHo(2) trimer plane. Good correlation between the experimental and computational IE data imply that the lowest energy neutral structures calculated are the most likely isomers ionized in the molecular beam. In particular, the theoretical adiabatic IE for the dissociative RhHo(2)O(2) structure is found to compare better with the experimentally determined value than the corresponding lowest energy O(2) associative structure.

We have used photo-ionisation efficiency spectroscopy to determine the ionisation potentials (IPs) of the niobium-carbide clusters, Nb(5)C(y) (y = 0-6). Of these clusters Nb(5)C(2) and Nb(5)C(3) exhibit the lowest IPs. Complementary density functional theory calculations have been performed to locate the lowest energy isomers for each cluster. By comparing the experimental IPs with those calculated for candidate isomers, the structures of the Nb(5)C(y) clusters observed in the experiment are inferred. For all these structures, the underlying Nb(5) cluster has either a "prolate" or "oblate" trigonal bipyramid geometry. Both Nb(5)C(5) and Nb(5)C(6) are shown to contain carbon-carbon bonding in the form of one and two molecular C(2) units, respectively.

We have used photoionization efficiency spectroscopy to determine ionization potentials (IP) of the niobium-carbide clusters, Nb3C(n) (n = 1-4) and Nb4C(n) (n = 1-6). The Nb3C2 and Nb4C4 clusters exhibit the lowest IPs for the two series, respectively. For clusters containing up to four carbon atoms, excellent agreement is found with relative IPs calculated using density functional theory. The lowest energy isomers are mostly consistent with the development of a 2 x 2 x 2 face-centered cubic structure of Nb4C4. However, for Nb3C4 a low-lying isomer containing a molecular C2 unit is assigned to the experimental IP rather than the depleted 2 x 2 x 2 nanocrystal isomer. For Nb4C5 and Nb4C6, interpretation is less straightforward, but results indicate isomers containing molecular C2 units are the lowest in energy, suggesting that carbon-carbon bonding is preferred when the number of carbon atoms exceeds the number of metal atoms. A double IP onset is observed for Nb4C3, which is attributed to ionization from the both the lowest energy singlet state and a meta-stable triplet state. This work further supports the notion that IPs can be used as a reliable validation for the geometries of metal-carbide clusters calculated by theory.