Spectral properties of superfluorescent pulses

We present a spectral analysis of the early stage of superfluorescent pulses. For systems with a Fresnel number near unity and a length long compared to the wavelength of the emitted radiation we find no perceptible frequency shifts or chips.     

Optische Aktivität und Magnetrotation als Beiträge zur chemischen Bindung und zur Elektronenkonfiguration der 1. Periode des Systems der Elemente (1). Teil I

Ohne ZusammenfassungHerrn Prof. Dr. Micheel Zum 60. Geburtstag gewidmet.     

On the Connection of Uncertainty Principles for Functions on the Circle and on the Real Line

An uncertainty principle for 2-periodic functions and the classical Heisenberg uncertainty principle are shown to be linked by a limit process. Dependent on a parameter, a function on the real line generates periodic functions either by periodization or sampling. It is proven that under certain smoothness conditions, the periodic uncertainty products of the generated functions converge to the real-line uncertainty product of the original function if the parameter tends to infinity. These results are used to find asymptotically optimal sequences for the periodic uncertainty principle, based either on Theta functions or trigonometric polynomials obtained by sampling B-splines.     

Configuration selection as a route towards efficient vibrational configuration interaction calculations

A configuration selective vibrational configuration interaction (CI) approach is presented that efficiently reduces the variational space and thus leads to significant speedups in comparison to standard vibrational CI implementations. Deviations with respect to reference calculations are well below the accuracy of the underlying electronic structure calculations for the potential and hence are essentially negligible. Parallel implementations of the presented configuration selective vibrational CI approaches lead to further significant time savings. Benchmark calculations based on potential energy surfaces of coupled-cluster quality are presented for the fundamental modes of cis- and trans-difluoroethylene. The size-consistency error within the vibrational configuration interaction calculations of the difluoroethylene dimer has been studied in dependence on the excitation level.     

Density functional based vibrational study of conformational isomers: Molecular rearrangement of benzofuroxan

The molecular rearrangement of benzofuroxan was studied by comparing calculated and experimental IR spectra, the latter taken before and during the reaction. All calculations were performed at the B3-LYP/6-31G(d) density functional level with a further refinement of the computed force constants done by applying the scaled quantum mechanical force field (SQM) technique. Complete assignments for the IR spectra of benzofuroxan and nitrosobenzene are given. The agreement between computed and experimental spectra is excellent, but in benzofuroxan these spectra are very different from previously calculated data. The conformation of the ortho-dinitrosobenzene intermediate of this tautomeric reaction was identified by modeling a composite IR spectrum of four possible components. It shows good agreement with an experimental spectrum that was obtained after photolysing benzofuroxan in Xe matrix. Knowing the conformation of the intermediate provides insight into the reaction mechanism and allows inferences for the thermal reaction, which could not be clarified conclusively by energetic considerations only. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 489–500, 1997     

Vibrational analyses for CHFClBr and CDFClBr based on high level ab initio calculations

Anharmonicity corrections to the harmonic vibrational spectra of CHFClBr and its deuterated isotopomer were computed by means of variational and perturbational approaches. A comparison of both methods is provided. Based on CCSD(T)/aug-cc-pVTZ electronic structure calculations excellent agreement with experimental data was obtained. Absolute mean deviations are in the range of about 4 cm(-1) for the fundamental modes, while slightly larger values of about 7 cm(-1) were found for the first vibrational overtones. In addition, vibrationally averaged structural parameters are provided for both molecules. The calculations will serve as a future starting point for parity-violation effects in vibrational transitions in these chiral molecules.     

Fingerprints of delocalized transition states in quantum dynamics

Reactions with delocalized transition states (plateau reactions) can be characterized statically by their energy profile along the reaction path, where they exhibit a broad, flat region instead of one or several well-defined saddle points on the potential energy surface. Employing our new, highly flexible quantum dynamics code to perform two-dimensional and effective four-dimensional quantum wave packet propagations on ab initio based model potentials, we show that plateau reactions can also be discerned from the other standard reaction types by their dynamics.     

The Triplet Hydroxyl Radical Complex of Phosphorus Monoxide

Phosphorus monoxide (^.PO) is a key intermediate in phosphorus chemistry, and its association with the hydroxyl radical (^.OH) to yield metaphosphorous acid (cis-HOPO) contributes to the chemiluminescence in the combustion of phosphines. When photolyzing cis-HOPO in an Ar-matrix at 2.8 K, the simplest dioxophosphorane HPO₂ and an elusive hydroxyl radical complex (HRC) of ^.PO form. This prototypical radical-radical complex reforms into cis-HOPO at above 12.0 K by overcoming a barrier of 0.28±0.02 kcal mol⁻¹. The vibrational spectra of this HRC and its D- and ¹⁸O-isotopologues suggest a structure of ^.OH⋅⋅⋅OP^., for which a triplet spin multiplicity with a binding energy of −3.20 kcal mol⁻¹ has been computed at the UCCSD(T)-F12a/aug-cc-pVTZ level.