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Transient grating (TG) spectroscopy has been applied to the photoinduced hydrogen-abstraction reaction of benzophenone (BP) in various kinds of room temperature ionic liquids (RTILs). After the photoexcitation of BP in RTILs, the formation of a benzophenone ketyl radical (BPK) was confirmed by the transient absorption method, and the TG signal was analyzed to determine the diffusion coefficients of BPK and BP. For comparison, diffusion coefficients of carbon monoxide (CO), diphenylacetylene (DPA), and diphenylcyclopropenone (DPCP) in various RTILs were determined by the TG method using the photodissociation reaction of DPCP. While the diffusion coefficients of the stable molecules BP, DPA, and DPCP were always larger than those predicted by the Stokes–Einstein (SE) relation in RTILs, that of BPK was much smaller than those of the stable molecules and relatively close to that predicted by the SE relation in all solvents. For the smallest molecule CO, the deviation from the SE relation was evident. The diffusion coefficients of stable molecules are better represented by a power law of the inverse of the viscosity when the exponent was less than unity. The ratios of the diffusion coefficient of BP to that of BPK were larger in RTILs (2.7–4.0) than those (1.4–2.3) in conventional organic solvents. The slow diffusion of BPK in RTILs was discussed in terms of the fluctuation of the local electric field produced by the surrounding solvent ions. [ABSTRACT FROM AUTHOR]

We report the photodissociation of laboratory oriented OCS molecules. A molecular beam of OCS molecules is hexapole state-selected and spatially oriented in the electric field of a velocity map imaging lens. The oriented OCS molecules are dissociated at 230 nm with the linear polarization set at 45° to the orientation direction of the OCS molecules. The CO(ν=0,J) photofragments are quantum state-selectively ionized by the same 230 nm pulse and the angular distribution is measured using the velocity map imaging technique. The observed CO(ν=0,J) images are strongly asymmetric and the degree of asymmetry varies with the CO rotational state J. From the observed asymmetry in the laboratory frame we can directly extract the molecular frame angles between the final photofragment recoil velocity and the permanent dipole moment and the transition dipole moment. The data for CO fragments with high rotational excitation reveal that the dissociation dynamics is highly nonaxial, even though conventional wisdom suggests that the nearly limiting β parameter results from fast axial recoil dynamics. From our data we can extract the relative contribution of parallel and perpendicular transitions at 230 nm excitation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

• The influence of molecular orientation on predissociation is discussed. • The angular distribution of dissociated products is influenced by molecular orientation. • The dissociation probability could be effectively improved after molecular orientation. Based on the time-depend quantum wave packet method, a scheme is proposed to investigate the effect of the molecular orientation on the predissociation of NaI molecules. The molecular orientation in the ground state is steered by THz half-cycle pulse. Then the oriented molecule is excited by femtosecond pump pulse. Molecular orientation has a significant effect on the angular distribution of wave packets. The excited wave packet is distributed in a more narrow region with the increase of molecular orientation degree. The angular distribution of dissociated products is essentially consistent with the angular distribution of excited wave packet. The dissociation probability is proportional to the excitation probability of pump pulse, which is related to the molecular orientations. Compared with the result of predissociation without molecular orientation, the maximal dissociation probability can increase by 6.5% in our work. The electric field intensity of the pump pulse also has a significant influence on dissociation probability. [ABSTRACT FROM AUTHOR]

The article discusses the work of Küpper, Stapelfeldth and colleagues which demonstrates the separation of conformational isomers using the electric field in a molecular-beam electrostatics deflector. In this experiment, the researchers selectively steer individual conformers who have different dipole moments through the employment of an homogeneous electric field. It explains that the different dipole moments of the conformers lead to differing degrees of deflection causing only one isomer to arrive at the interaction region. It notes that method opens the way for future researches on photodissociation or reaction dynamics involving isomers.