We demonstrate the potential of velocity map ion imaging methods for high resolution studies of the photofragmentation of a state selected molecular ion, Br 2 + . 79 Br 2 + cations were prepared in the v + ¼ 1 levels of both spin-orbit components of the X 2 P g ground state by 2 + 1 resonance enhanced multiphoton ionisation (REMPI) of jet-cooled, isotopomer-selected 79 Br 2 molecules at an excitation wavelength of 263.012 nm. The subsequent photolysis of these state selected ions was then investigated in the wavelength range 372 < l phot < 432 nm by imaging the resulting 79 Br + ions. Use of a home-built Pockels cell assembly allowed measurement of images with and without l phot present, on successive laser shots. The resulting difference image allows clear visualisation of the parent ion fragmentation, free from unintended fragment ion signal induced by the REMPI preparation step. The images reveal participation of dissociation channels yielding Br + ions in both their ground ( 3 P 2 ) and first excited ( 3 P 1 ) spin-orbit states, together with ground state Br atoms. No fragmentation channels involving formation of spin-orbit excited Br( 2 P 1/2 ) atoms are found to be active in this range of photolysis wavelengths. Image analysis yields a precise value for the bond strength of the Br 2 + cation, in both spin-orbit components of its ground electronic state: D 0 [ 79 Br 2 + (X 2 P 1/2,g )] ¼ 23528.1 AE 0.6 cm À1 and D 0 [ 79 Br 2 + (X 2 P 3/2,g )] ¼ 26345 AE 2 cm À1 , and thus a refined measure of the spin-orbit splitting in the ground state Br 2 + cation: A ¼ 2817 AE 3 cm À1 .

The photodissociation dynamics of jet-cooled BrCl molecules have been investigated at four different wavelengths in the range 425–485 nm by high-resolution velocity map ion imaging. Four images of the Cl(2P3/2) atomic fragments are recorded at each photolysis wavelength with the probe laser polarization, respectively, linearly aligned and vertical (i.e., perpendicular to the detection axis), right circularly polarized, horizontally linearly polarized (i.e., parallel to the detection axis) and left circularly polarized on successive laser shots, thereby ensuring automatic mutual self-normalization. Appropriate linear combinations of these images allow quantification of the angular momentum alignment of the Cl(2P3/2o) fragments [i.e., the correlation between their recoil velocity (v) and their electronic angular momentum (J)] in terms of the alignment anisotropy parameters s2, α2, η2, and γ2, and determination of the “alignment-free” recoil anisotropy parameter, β0, as a function of parent excitation wavelength. Both incoherent and coherent contributions to the alignment are identified, with both simultaneous parallel and perpendicular excitations to the B 3Π(0+) and C 1Π(1) states and excitations to the Ω=±1 components of the C state contributing to the latter. The deduced values of the alignment-free β parameters indicate (wavelength dependent) contributions from both parallel and perpendicular parent absorptions in this wavelength range. Such a conclusion accords with approximate deconvolutions of the parent absorption spectrum that are currently available, and with determinations of the orientation parameter γ1′ obtained by fitting the difference image obtained when using left and right circularly polarized radiation to probe the ground state Cl atoms arising in the 480.63 nm photodissociation of BrCl when the photolysis laser radiation is polarized linearly at 45° to the detection axis.

In this study we examine graphene with different shape, size, functionality and electrical conductivity as carbon nanofiller for epoxy (EP) composites. Thermally reduced graphite oxide (TRGO) and a nitrogen doped derivative (N-TRGO) are compared with multilayer graphene (MLG) derived from milling of graphite. Whereas wet grinding of graphite forms stable non-functionalized MLG dispersions, solvent free dry grinding of graphite under N 2 and CO 2 pressure allows for mechanochemical functionalization of graphite. TRGO and N-TRGO show best exfoliation, highest electrical conductivity and efficient matrix reinforcement at low percolation threshold. As compared to TRGO, wet and dry grinding represent cost-effective routes to MLG and afford EP composites with improved stiffness at higher filler content. These fillers offer great promise for application in carbon/polymer composites going well beyond the scope of epoxy resins.

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Articles you may be interested inVelocity map imaging study of BrCl photodissociation at 467 nm: Determination of all odd-rank ( K = 1 and 3) anisotropy parameters for the Cl ( P 3 ∕ 2 0 2 ) photofragments J. Chem. Phys. 124, 094305 (2006); 10.1063/1.2168149The matrix-isolated molecular complexes CO /X F (X= Cl,Br,I ) and the molecular structure of FC(O)Br Continuum state spectroscopy: A high resolution ion imaging study of IBr photolysis in the wavelength range 440-685 nm Ion imaging studies of the Cl ( 2 P J ) and Br ( 2 P J ) atomic products resulting from BrCl photodissociation in the wavelength range 235-540 nmThe photodissociation of jet-cooled BrCl molecules has been investigated at many different excitation wavelengths in the range 330-570 nm by velocity map imaging of the ground state Br and ground and spin-orbit excited Cl atom products. Image analysis confirms literature values for the energies of the ground, Br( 2 P 3/2 )ϩCl( 2 P 3/2 ), and first excited ͓Br( 2 P 3/2 )ϩCl( 2 P 1/2 )͔ dissociation asymptotes, and provides measures of the electronic branching into these two active product channels, and the recoil anisotropy of each set of products, as a function of parent vibrational level (vЉр2) and excitation wavelength. The availability of such experimental data allows mapping of the partial cross-sections for parallel ͑i.e., ⌬⍀ϭ0͒ and perpendicular ͑i.e., ⌬⍀ϭϮ1͒ absorption as a function of excitation energy, and thus deconvolution of the room temperature parent absorption spectrum into contributions associated with excitation to the A 3 ⌸(1), B 3 ⌸(0 ϩ ), and C 1 ⌸(1) excited states of BrCl. This analysis of the continuous absorption spectrum of BrCl, when considered in conjuction with existing spectroscopic data for the ground electronic state and for the bound levels supported by the B state potential, allows determination of key regions of the potential energy curves for, and transition moments to, each of these three excited states. Further wave packet calculations, which reproduce the experimentally measured wavelength dependent product channel branching ratios and product recoil anisotropies very well, serve to validate the excited state potential energy functions so derived and allow estimation of the strength ͑ϳ80 cm Ϫ1 ͒ of the coupling between the bound ͑B͒ and dissociative ͑Y͒ diabatic states of 0 ϩ symmetry.