The microwave spectra of thiophene and 2-acetylthiophene were recorded in the frequency range from 2 to 40 GHz using two molecular jet Fourier transform microwave spectrometers. For 2-acetylthiophene, two conformers...

Glycols are accessible via metal-catalyzed hydrogenolysis of sugar alcohols such as xylitol obtained from hemicellulose. Rubased catalysts are highly active but also catalyze side-reactions such as decarbonylation and deoxygenation. To achieve high selectivity, these reactions need to be suppressed. In our study, we introduce heteroatom doped carbon materials as catalyst supports providing high selectivity. Heteroatom doping with nitrogen and oxygen was achieved by treating activated carbon with HNO 3 , NH 3 and H 2 or carbonization of organic precursors.For all N-doped materials a high glycol selectivity of �80 % for sorbitol and xylitol and 44 % for xylose and glucose was reached. XPS analysis confirms the presence of different nitrogen species at the carbon surface and varying ligand effects for oxygen and nitrogen. Oxygen has an electron withdrawing effect on ruthenium and leads to a decreased activity. Nitrogen has weaker electron withdrawing properties, resulting in an enhanced selectivity.

The dissociation energies of four transition metal dimers are determined using diffusion Monte Carlo. The Jastrow, CI, and molecular orbital parameters of the wave function are both partially and fully optimized with respect to the variational energy. The pivotal role is thereby ascribable to the optimization of the molecular orbital parameters of a complete active space wave function in the presence of a Jastrow correlation function. Excellent results are obtained for ZnO, FeO, FeH, and CrS. In addition, potential energy curves are computed for the first three compounds at multi-reference diffusion Monte Carlo (MR-DMC) level, from which spectroscopic constants such as the equilibrium bond distance, the harmonic frequency, and the anharmonicity are extracted. All of those quantities agree well with the experiment. Furthermore, it is shown for CrS that a restricted active space calculation can yield improved initial orbitals by including 1 single and double excitations from the original active space into a set of virtual orbitals.We demonstrated in this study that the fixed-node error in DMC can be systematically reduced for multi-reference systems by orbital optimization in compact active spaces.While DMC calculations with a large number of determinants are possible and very accurate, our results demonstrate that compact wave functions may be sufficient in order to obtain accurate nodal surfaces, which determine the accuracy of DMC, even in the case of transition metal compounds.

The 1Σg + ground state of C2 is investigated using truncated CIPSI-Jastrow CSF wave functions with Hartree–Fock orbitals within the framework of variational and diffusion quantum Monte Carlo. The truncation is performed based on the absolute value of the CI coefficients, and the Jastrow, molecular orbitals, and CI parameters are either partially or fully reoptimized with respect to the variational energy. Excellent absolute as well as bond dissociation energies are obtained at DMC level with very compact, fully optimized wave functions. By studying the expansions in more detail, we observe a change in the CI picture when reoptimizing the antisymmetric part of the CIPSI-Jastrow wave functions. Furthermore, we demonstrate that a decrease in the VMC energy as well as an improvement of the nodal surface quality can be achievedwith the same expansion sizeif the CSFs are selected in the presence of a Jastrow correlation function, laying the foundation for a Jastrow selected CI scheme with quantum Monte Carlo.

The concept of distinct bonds within molecules has proven to be successful in rationalizing chemical reactivity. However, bonds are not a well-defined physical concept, but rather vague entities, described by different and often contradicting models. With probability density analysis, which can---in principle---be applied to any wave function, bonds are recovered as spin-coupled positions within most likely electron arrangements in coordinate space. While the wave functions of many systems are dominated by a single electron arrangement which is built from two-center two-electron bonds, some systems require several different arrangements to be well described. In this work, a range of these multi-center bonded molecules are classified and investigated with probability density analysis. The results are compared with valence bond theory calculations and data from collision-induced dissociation experiments.