The economic ecology of small businesses in Oxfordshire

Report by the Oxfordshire Economic Observatory (OEO) for the Federation of Small Businesses (FSB), Oxfordshire Branch

Measuring surface phonons using molecular spin-echo

A new method to measure surface phonons with a molecular beam is presented

Temperature dependent stereodynamics in surface scattering measured through subtle changes in the molecular wave function

A magnetically manipulated molecular beam technique is used to change the rotational orientation of H2 molecules which collide with a stepped Cu(511) surface and explore how the polarisation dependence of molecules scattering into the specular channel changes as a function of surface temperature. At all temperatures, H2 molecules that are rotating like cartwheels are more likely to be scattered into the specular channel than those that are rotating like helicopters. Furthermore, the scattered molecules are more likely to be rotating like cartwheels, regardless of their state before the collision. Increasing the temperature of the Cu(511) surface causes the polarisation effects to become stronger, with the scattering becoming more selective for H2 with cartwheel like rotation. Therefore, scattering a molecular beam of H2 from a Cu(511) surface and taking the molecules scattered into the specular channel provides a method to create a rotationally polarised beam of H2, where the polarisation can be tuned by changing the surface temperature. In contrast, the rotational orientation dependence observed for specular scattering from a flat Cu(111) surface is independent of surface temperature within the same temperature range

Planning decision support tools for sustainable development and renewable energy.

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Stopping molecular rotation using coherent ultra-low-energy magnetic manipulations

Rotational motion lies at the heart of intermolecular, molecule-surface chemistry and coldmolecule science, motivating the development of methods to excite and de-excite rotations.Existing schemes involve perturbing the molecules with photons or electrons which supply orremove energy comparable to the rotational level spacing. Here, we study the possibility ofde-exciting the molecular rotation of a D2 molecule, from J = 2 to the non-rotatingJ = 0 state, without using an energy-matched perturbation. We show that passing the beamthrough a 1 m long magnetic field, which splits the rotational projection states by only10−12 eV, can change the probability that a molecule-surface collision will stop a moleculefrom rotating and lose rotational energy which is 9 orders larger than that of the magneticmanipulation. Calculations confirm that different rotational orientations have different deexcitation probabilities but underestimate rotational flips (ΔmJ≠0), highlighting the importance of the results as a sensitive benchmark for further developing theoretical models ofmolecule-surface interactions

CHD3 Dissociation on the Kinked Pt(210) Surface: A Comparison of Experiment and Theory

To be able to simulate activated heterogeneously catalyzed reactions on the edge and corner sites of nanoparticles, a method for calculating accurate activation barriers for the reactions is required. We have recently demonstrated that a semiempirical specific reaction parameter (SRP) density functional developed to describe CHD3 dissociation on a flat Ni(111) surface is transferable to describing the same reaction on a stepped Pt(211) surface. In the current work, we compare initial sticking coefficients measured using the King and Wells beam reflectivity technique and calculated from ab initio molecular dynamics trajectories using the same SRP functional for CHD3 dissociation on a kinked Pt(210) surface at a temperature of 650 K. The calculated sticking coefficients overestimate those determined experimentally, with an average energy shift between the two curves of 13.6 kJ/mol, which is over a factor of 3 times higher than the 4.2 kJ/mol limit that defines chemical accuracy. This suggests the SRP functional predicts an activation barrier that is too low for the dissociation on the least coordinated kink atom, which is the site of the lowest energy transition state and where most of the dissociation occurs in the calculations

Quantum state resolved molecular beam reflectivity measurements: CH4 dissociation on Pt(111)

The King and Wells molecular beam reflectivity method has been used for a quantum state resolved study of the dissociative chemisorption of CH4 on Pt(111) at several surface temperatures. Initial sticking coefficients were measured for incident CH4 prepared both with a single quantum of antisymmetric stretch vibration by infrared laser pumping, and without laser excitation. Vibrational excitation of the mode is observed to be less efficient than incident translational energy in promoting the dissociation reaction with a vibrational efficacy = 0.65. The initial state resolved sticking coefficient was found to be independent of the surface temperature over the 50kJ/mol to 120kJ/mol translational energy range studied here. However, the surface temperature dependence of the King and Wells data reveals the migration of adsorbed carbon formed by CH4 dissociation on the Pt(111) surface leading to the growth of carbon particles