Fully rotationally resolved ZEKE photoelectron spectroscopy of C6H6 and C6D6: photoionization dynamics and geometry of the benzene cation

A comprehensive set of spectra for the benzene cation and the perdeuterated benzene cation has been recorded with full rotational resolution using zero kinetic energy photoelectron spectroscopy (ZEKE) at high resolution (up to 0.2 cm^?1), using a slow-rising extraction pulse. With different rovibronic levels in the S₁ 6^l state as intermediate resonance, the rotational transitions to the vibronic ground state of the cation have been recorded using two-colour, two-photon resonance enhanced multiphoton ionization. A simple spectator model has been employed to simulate the intensities of the ZEKE transitions. By fitting the simulations to the recorded spectra, improved values for the rotational constants and the Coriolis coupling parameters of benzene and perdeuterated benzene have been obtained. The CC and CH bond lengths of the cation have been deduced. The spectator model is shown to be reliable despite the fact that no specific allowance is made for the effect of final state interactions on the signal intensity.     

Microcanonical equilibrium properties of chiral liquid crystals—a Monte Carlo study

Chiral liquid crystals have been investigated by means of a multicanonical Monte Carlo approach in order to characterize their phase behaviour by microcanonical equilibrium properties. The liquid crystals were described by three-dimensional lattice systems with intermolecular interactions given by the chiral Lebwohl-Lasher potential. Self-determined boundary conditions have been applied in order to enable the formation of chiral phases with equilibrium pitch. Selected thermodynamic properties, e.g. microcanonical entropy, temperature, heat capacity and a set of order parameters have been determined with dependence on microcanonical total energy. A cholesteric phase with temperature-induced helix inversion could be proven where the helical superstructure of the single component system studied changed its handedness through an infinite-pitch system. The thermodynamical behaviour in the microcanonical ensemble was found to be very similar to the behaviour in the canonical ensemble. The study of microcanonical equilibrium properties by means of multicanonical Monte Carlo simulations was shown to be a powerful tool for the study of the phase behaviour of model liquid crystals.     

An efficient method for calculating the pair distribution functions of a ternary hard-sphere system in r space within the Percus-Yevick approximation

We present a direct method which allows an accurate and—at the same time—economical calculation of the pair distribution functions (PDFs) g_ij (r) of an additive ternary hard-sphere system within the Percus—Yevick approximation. The approach is based on the fact that for this approximation the Laplace transforms [?_ij (s)] of the PDFs are known analytically, so that the inversion of the ?_ij (s) into r space can be performed exactly. The expressions presented here allow the determination of the ?_ij (r) for r values up to 8R ₁, R ₁ being the diameter of the smallest species; this range in r space should be sufficient for applications in standard algorithms of liquid state theory, such as thermodynamic perturbation theories or integral-equation approaches.