Volume 114, Issue 1, 01 January 2001
Index of content:
Temperature dependence of inclusion-dissociation behavior between molecular nanotubes and linear polymers114(2001); http://dx.doi.org/10.1063/1.1334599View Description Hide Description
We have investigated the inclusion-dissociation behavior between molecular nanotubes and linear polymers in solutions by measuring the induced circular dichroism of the mixture of the molecular nanotubes, which are composed of α-cyclodextrins linked by three cross-linking bridges, and poly(ethylene glycol) modified with azobenzene. It was found that the inclusion complex between the nanotubes and the linear polymers was formed at room temperature, and that the polymers were dissociated from the nanotubes with increasing temperature, as expected theoretically.
114(2001); http://dx.doi.org/10.1063/1.1334905View Description Hide Description
The atom reaction with ethane has been investigated using crossed molecular beam techniques. Four different reaction channels have been observed. Distinctive product angular distributions have also been observed for these reaction channels, indicating these reaction channels proceed via different dynamical pathways. These detailed experimental investigations provide a full dynamical picture of this reaction and also an important link between chemical reactiondynamics and kinetics studies. The experimental results presented here also provide an excellent test ground for developing quantitative theoretical understandings of multiple channel reactiondynamics for this interesting reaction.
114(2001); http://dx.doi.org/10.1063/1.1336545View Description Hide Description
Photofragmentation of glyoxal, under collision free conditions proceeds by internal conversion from to vibrationally excited which is observed to dissociate into and Early molecular orbital calculations placed the barrier for the formaldehyde channel 12–20 kcal/mol above the three body fragmentation channel, contrary to what would have been expected from the branching ratios. The best calculational estimate of the barrier for the three body fragmentation was ≈8 kcal/mol higher than the reported activation energy for the thermal decomposition of glyoxal. These problems have been resolved by the more accurate ab initio molecular orbital calculations reported in the present note. With the complete basis set extrapolation method of G. Petersson and co-workers using an atomic pair natural orbital basis set (CBS-APNO), the calculated heats of reaction that are within 0.4–0.8 kcal/mol of the experimental values for and 2 HCO. The barrier computed for is 54.4 kcal/mol, in excellent agreement with the high pressure limit of the activation energy for thermal decomposition of glyoxal. The computed barrier for the three body fragmentation is 4.8 kcal/mol higher than the channel, in agreement with the observed lower yield for this channel.
114(2001); http://dx.doi.org/10.1063/1.1334956View Description Hide Description
Diffusion of a five-site model of methane within porous zeolite A has been investigated by molecular dynamics simulation using potential available in the literature. Equilibrium and dynamical quantities especially those relating to the orientational degrees of freedom of methane have been computed. Methane exhibits interesting orientational preference during intercage diffusion through the eight-membered window which is the rate determining step for diffusion. A predominance of (2+2) orientation in place of (1+3) orientation is seen suggesting a strong translational–orientational coupling. This suggests that orientational motion might strongly influence the translational diffusivity of methane.