Jürgen Breidung

The vibrational spectra of krypton and xenon difluoride: High‐resolution infrared studies and ab initio calculations

Fourier transform infrared spectra of KrF2, XeF2, and monoisotopic 136XeF2 have been recorded in the ν3 and ν1+ν3 ranges with an effective resolution of 0.003–0.007 cm−1. About 10 000 rovibrational lines belonging to cold bands and to hot bands with ν1, ν2, 2ν2, and ν3 as lower levels have been assigned and fitted. The high‐resolution results from this work and from two previous studies provide a rather complete set of precise spectroscopic constants and accurate ground‐state and equilibrium geometries for both molecules. In the case of 84KrF2, r0=188.2821(9) pm supersedes previous incorrect r0 values, and re=187.6930(23) pm represents the first determination of the Kr–F equilibrium distance. Ab initio calculations employing effective core potentials and polarized double‐zeta basis sets have been carried out at the following levels: self‐consistent‐field (SCF) theory, the Mo/ller–Plesset second order perturbation theory (MP2), and coupled cluster theory with single and double excitations (CCSD) and a pert...

The Equilibrium Structure of Methyl Fluoride

AbstractThe equilibrium structure of CH3F has been determined using new sets of accurate rotational constants that have been determined by taking into account all the interactions between the excited vibrational states. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with the cc-pV(5, Q)Z basis set (including corrections for the core correlation and for the effect of diffuse functions on fluorine). Finally, the experimental and ab initio structures have been combined by a least-squares analysis. The results are

The equilibrium structure of silene H2C=SiH2 from millimeter wave spectra and from ab initio calculations

r_e \left( {C - C} \right) = 1.087\left( 1 \right){\AA},r_e \left( {C - F} \right) = 1.383\left( 1 \right){\AA},and\angle _e \left( {HCH} \right) = 110.2\left( 1 \right)^ \circ

Correlated Ab Initio and Density Functional Studies on H2 Activation by FeO(.).

, and Le(HCH) = 110.2 (1)°, where the uncertainties shown in parentheses correspond to three standard deviations.

Ab initio calculations and high resolution infrared investigation on XeF4

We report potential-energy and free-energy data for three enzymatic reactions: carbon–halogen bond formation in fluorinase, hydrogen abstraction from camphor in cytochrome P450cam, and chorismate-t...

Analytical Second Derivatives for Effective Core Potentials

Silene, H2CSiH2, has been efficiently produced by pyrolysis of 5,6-bis(trifluoromethyl)- 2-silabicyclo[2.2.2]octa-5,7-diene (SBO). Seven isotopomers have been observed by millimeter- and submillimeter-wave spectroscopy. From the different sets of experimental molecular parameters and from ab initio calculations of the rovibrational interaction parameters, the equilibrium structure has been obtained by a least squares analysis of the rotational constants. The results are: re(Si=C)=1.7039(18) A, re(C–H)=1.0819(12) A, re(Si–H)=1.4671(9) A, ∠HCSi=122.00(4)°, and ∠HSiC=122.39(3)°. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with a cc-pV(Q,T)Z basis set. This is the first experimental determination without any constraint of the Si=C double bond length in the parent compound of the silaalkene family. A lifetime of 30 ms has been observed for this molecule in the gas phase at low pressure.

Ab initio anharmonic force field, spectroscopic parameters and equilibrium structure of trifluorosilane

The recent implementation of analytic second derivatives for CCSD(T) (coupled cluster theory with single and double excitations augmented by a perturbational treatment of connected triple excitations) has been combined with a numerical finite difference procedure to calculate cubic and semidiagonal quartic force fields. Computational details of this approach are outlined. Applications are reported for HOF and F2O. The CCSD(T) results are in excellent agreement with experiment and represent a substantial improvement over the results obtained from MP2 (Mo/ller–Plesset second-order perturbation theory).

The anharmonic force fields of PH3, PHF2, PF3, PH5, and H3PO

The reaction FeO(+) + H2 → Fe(+) + H2O is a simple model for hydrogen abstraction processes in biologically important heme systems. The geometries of all relevant stationary points on the lowest sextet and quartet surfaces were optimized using several density functionals as well as the CASSCF method. The corresponding energy profiles were computed at the following levels: density functional theory using gradient-corrected, hybrid, meta, hybrid-meta, and perturbatively corrected double hybrid functionals; single-reference coupled cluster theory including up to single, double, triple, and perturbative quadruple excitations [CCSDT(Q)]; correlated multireference ab initio methods (MRCI, MRAQCC, SORCI, SORCP, MRMP2, NEVPT2, and CASPT2). The calculated energies were corrected for scalar relativistic effects, zero-point vibrational energies, and core-valence correlation effects. MRCI and SORCI energies were corrected for size-consistency errors using an a posteriori Davidson correction (+Q) leading to MRCI+Q and SORCI+Q. Comparison with the available experimental data shows that CCSDT(Q) is most accurate and can thus serve as benchmark method for this electronically challenging reaction. Among the density functionals, B3LYP performs best. In the correlated ab initio calculations with a full-valence active space, SORCI+Q yields the lowest deviations from the CCSDT(Q) reference results, with qualitatively similar energy profiles being obtained from MRCI+Q and MRAQCC. SORCI+Q benefits from the quality of the approximate average natural orbitals used in the final step of the SORCI procedure. Many of the tested methods show surprisingly large errors. The present results validate the common use of B3LYP in computational studies of heme systems and offer guidance on which correlated ab initio methods are most suitable for such studies.