Theoretical and experimental studies of molecular motions and reaction mechanisms

Abstract

The time-delayed forwards scattering mechanism recently observed by Althorpe et al. [1] for the H + D2 (v=O, j=O) --? HD(v'=3, j'=O) + D reaction was analysed using the quasi-classical trajectory (QCT) methodology. QCT's were found to reasonably match the quantum snapshots of Althorpe, without the quantum effects. Trajectories were analysed on the fly to investigate the motions of the atoms during the reaction. The dominant reaction mechanism progresses from hard collinear impacts, leading to direct recoil, to glancing impacts. The increased time required for forward scattered trajectories is due to the rotation of the HDD complex. Forwards scattered trajectories display symmetric stretch vibrations of the HDD complex, indicating the presence of a resonance or a quantum bottleneck state. Reactive scattering in the HD(v'=O, j'=O) product channel was found to be governed by two unexpected and dominant new mechanisms, and not by direct recoil as is generally assumed. The new mechanisms involve strong interaction with the conical intersection, an area of the potential energy surface not previously thought to have much effect upon reactive scattering. Initial investigations indicate up to 56% of reactive scattering could be the result of these mechanisms.UV Cavity Ring-Down Spectroscopy of 1, 4-bis(phenylethynyl}benzene The torsional motion of 1, 4 bis(phenylethynyl)benzene (BPEB), a prototype molecular wire, is important for switching in molecular electronics. Cavity ring-down spectroscopy was used to record the torsional spectra of BPEB and 1, 4-bis(phenylethynyl) 2,3,5,6-tetradeuterobenzene in the gas phase. The spectra were modelled using a simple cosine potential. The experimental torsional barrier is very similar to the two ring system, Tolane. It was found that DFT calculations completely overestimate the torsional barrier.IV [brace not closed]