Photolysis Dynamics Laser Chemistry Lab

Atomic halogen elimination from halogen-related compounds plays a vital role in the depletion of the ozone layer and is well investigated. However, the probabilities for elimination of molecular halogens and hydrogen halides are rarely scrutinised. We develop distinct method for the investigation of each kind of fragment. Velocity-mapping ion-imaging was employed to study the atomic halogen elimination from alkyl halides and aryl halides, focusing on the fractions of the translational energy release, the quantum yields of the atomic fragments, transition probability for curve crossing, competitive halogen-related bond fission, and anisotropy parameters to understand their dynamical complexity. Cavity ring-down absorption spectroscopy was implemented to investigate the molecular halogen fragments dissociated from the aliphatic halides and acyl halides for their optical spectra, vibrational branches, quantum yields, and the dissociation mechanisms. Time-resolved Fourier transform infrared emission spectroscopy was employed to confine the primary products of hydrogen halide elimination from acyl halides in the presence of Ar gas. It is, for the first time, to overview these existing small halogen-related fragments eliminated from halogen-containing compounds. The detailed characterisation of these fragments should unveil complicated halogen-related dissociation mechanisms which may supplement the current knowledge and help with the photochemical assessment of halogen-related environmental issue. © 2020 Informa UK Limited, trading as Taylor & Francis Group.

Molecular orientation is a fundamental requisite in the study of stereodirected dynamics of collisional and photoinitiated processes. In this past decade, variable hexapolar electric filters have been developed and employed for the rotational-state selection and the alignment of molecules of increasing complexity, for which the main difficulties are their mass, their low symmetry, and the very dense rotational manifold. In this work, for the first time, a complex molecule such as 2-bromobutane, an asymmetric top containing a heavy atom (the bromine), was successfully oriented by a weak homogeneous field placed downstream from the hexapolar filter. Efficiency of the orientation was characterized experimentally, by combining time-of-flight measurements and a slice-ion-imaging detection technique. The application is described to the photodissociation dynamics of the oriented 2-bromobutane, which was carried out at a laser wavelength of 234 nm, corresponding to the breaking of the C-Br bond. The Br photofragment is produced in both the ground Br (2P3/2) and the excited Br (2P1/2) electronic states, and both channels are studied by the slice imaging technique, revealing new features in the velocity and angular distributions with respect to previous investigations on nonoriented molecules. © 2016 American Chemical Society.

Carbon mesoporous materials (CPMs) have great potential in the field of heterogeneous catalysis. Highly dispersed ruthenium nanoparticles (RuNPs) embedded in three dimensional (3D) CPMs as catalysts with a high surface area (1474 m2 g-1) were prepared by microwave-thermal reduction processes. Characterization technologies including X-ray diffraction (XRD), N2 adsorption/desorption isotherm measurements, field emission transmission electron microscopy (FE-TEM), thermogravimetric analysis (TGA), hydrogen temperature-programmed reduction (H2-TPR), Raman spectroscopy and 13C solid state cross polarization and magic angle spinning (13C CP/MAS) NMR spectroscopy were utilized to scrutinize the catalysts. It was revealed that the Ru/CPM catalysts exhibited a highly ordered 3D mesoporous structure and a large surface area and were widely used as catalysts for reduction reactions. Reduction of p-nitroaniline (p-NA) and crystal violet (CV) using NaBH4 with the use of this catalyst was studied by means of UV-vis spectroscopy. Here, NaBH4 acts as a hydrogen donor. This catalyst shows an excellent catalytic activity towards reduction of p-NA and CV dye at room temperature. Due to the promising properties of CPMs, they can be utilized to fabricate 3D carbon-based materials for a variety of novel applications. © The Royal Society of Chemistry 2015.

Polynorbornenes appended with anthracene and chiral alanine linkers are synthesized. Hydrogen bonding between the adjacent bisamidic linkers brings adjacent anthracene chromophores in a more suitable orientation for exciton coupling and renders one-handed helical structures for these polymers. Excimer formation is observed from their emission spectra. Monoamidic linkers provide only one hydrogen bond, which would be less robust and result in much lower circular dichroic response. Hydrogen bonding between the adjacent chiral alanine linkers brings appended anthracene in a more suitable orientation for exciton coupling and excimer formation, rendering one-handed helical structures in polynorbornenes. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.