Quantum Ignition of Intramolecular Rotation by Means of IR+UV Laser Pulses

Quantum ignition of intramolecular rotation may be achieved as follows: First, a few-cycle infrared (IR) laser pulse excites the torsional vibration in an oriented molecule. Subsequently, a well timed ultrashort ultraviolet (UV) laser pulse induces a Franck-Condon type transition from the electronic ground state to the excited state with approximate conservation of the intramolecular angular momentum. As a consequence, the torsional motion is converted into a unidirectional intramolecular rotation, with high angular momentum (≈ 100 h). The mechanism is demonstrated by means of representative laser driven wave packets which are propagated on ab initio potential energy curves of the model system (4-methyl-cyclohexylidene)fluoromethane

The role of dipole interactions in hyperthermia heating colloidal clusters of densely-packed superparamagnetic nanoparticles

This work aims to investigate the influence of inter-particle dipole interactions on hyperthermia heating colloidal clusters of densely-packed Fe3O4 nanoparticles at low field intensity. Emulsion droplet solvent evaporation method was used to assemble oleic acid modified Fe3O4 particles into compact clusters which were stabilized by surfactant in water. Both experimental and simulation works were conducted to study their heating performance at different cluster’s sizes. The dipole interactions improve the heating only when the clusters are small enough to bring an enhancement in clusters’ shape anisotropy. The shape anisotropy is reduced at greater clusters’ sizes, since the shapes of the clusters become more and more spherical. Consequently, the dipole interactions change to impair the heating efficiency at larger sizes. When the clusters are totally isotropic in shape, the heating efficiency is lower than that of non-interacting particles despite the cluster’s size, although the efficiency increases by a little bit at a particular size most likely due to the dipole couplings. In these situations, one has to use particles with higher magnetic anisotropy and/or saturation magnetization to improve the heating

Three-dimensional ab initio simulation of laser-induced desorption of NO from NiO(100)

Laser-induced desorption of NO molecules from a NiO(1 0 0) surface is studied on an ab initio level. Based on ab initio NiO-cluster calculations a three-dimensional potential energy surface was constructed for the electronic ground and a representative excited state. Quantum wave packet calculations on these surfaces allow the simulation of experimental velocity distributions of the desorbed NO molecules. Analysis of the wave packet dynamics demonstrates that the experimentally observed bimodality of the velocity distributions is caused by a bifurcation of the wave packet on the excited state potential, where the molecular motion parallel to the surface plays a decisive role

Photo-induced desorption of NO from NiO(100): calculation of the four-dimensional potential energy surfaces and systematic wave packet studies

The velocity distributions of the laser-induced desorption of NO molecules from an epitaxially grown film of NiO(100) on Ni(100) have been studied [Mull et al., J. Chem. Phys., 1992, 96, 7108]. A pronounced bimodality of velocity distributions has been found, where the NO molecules desorbing with higher velocities exhibit a coupling to the rotational quantum states J. In this article we present simulations of state resolved velocity distributions on a full ab initio level. As a basis for this quantum mechanical treatment a 4D potential energy surface (PES) was constructed for the electronic ground and a representative excited state, using a NiO5Mg18+13 cluster. The PESs of the electronic ground and an excited state were calculated at the CASPT2 and the configuration interaction (CI) level of theory, respectively. Multi-dimensional quantum wave packet simulations on these two surfaces were performed for different sets of degrees of freedom. Our key finding is that at least a 3D wave packet simulation, in which the desorption coordinate Z, polar angle and lateral coordinate X are included, is necessary to allow the simulation of experimental velocity distributions. Analysis of the wave packet dynamics demonstrates that essentially the lateral coordinate, which was neglected in previous studies [Klüner et al., Phys. Rev. Lett. 1998, 80, 5208], is responsible for the experimentally observed bimodality. An extensive analysis shows that the bimodality is due to a bifurcation of the wave packet on the excited state PES, where the motion of the molecule parallel to the surface plays a decisive role