Optimal control theory with continuously distributed target states: An application to NaK

Laser pulse control of molecular dynamics is studied theoretically by using optimal control theory. The control theory is extended to target states which are distributed in time as well as in a space of parameters which are responsible for a change of individual molecular properties. This generalized treatment of a control task is first applied to wave packet formation in randomly oriented diatomic systems. Concentrating on an ensemble of NaK molecules which are not aligned the control yield decreases drastically when compared with an aligned ensemble. Second, we demonstrate for NaK the maximization of the probe pulse transient absorption in a pump–probe scheme with an optimized pump pulse. These computations suggest an overall optical control scheme, whereby a flexible technique is suggested to form particular wave packets in the excited state potential energy surface. In particular, it is shown that considerable wave packet localization at the turning points of the first-excited Σ-state potential energy surfaces of NaK may be achieved. The dependency of the control yield on the probe pulse parameters is also discussed.     

Absorption spectra related to heterogeneous electron transfer reactions: the perylene TiO2 system

Linear absorption spectra of dye-semiconductor systems (perylene attached to nanostructured TiO2) are studied theoretically and experimentally. The systems show ultrafast photoinduced heterogeneous electron transfer (HET). By applying a time-dependent formulation of the absorbance, the theoretical analysis of the measured data is carried out. The respective electron-vibrational wave packet propagation fully accounts for the electronic coupling to the conduction band continuum of TiO2 and is based on a single-reaction-coordinate model (corresponding to a perylene in-plane C-C stretching vibration with a quantum energy of 1370 cm(-1)). By the insertion of different bridge-anchor groups, the electronic coupling responsible for HET is varied. The dye absorbance in a solvent and the trends in the line broadening of the vibrational progression due to the coupling to the conduction band continuum are reproduced for all investigated types of bridge-anchor groups. HET rates deduced from the calculations on the absorbance displaying line broadenings follow the qualitative trend obtained from transient absorption spectra.     

Observation of soft-modes in a single crystal of Rb2ZnBr4 by Raman scattering

The Raman spectra of an oriented single crystal of Rb₂ZnBr₄ shows three soft modes. One of them is interpreted as the amplitude mode of the incommensurate phase. The second one, seen well below the lock-in transition temperature appears as the phase mode. Moreover, an additional soft mode is observed between T=120 K and T=20 K, in the b(c, c)a scattering geometry. By extrapolation it is found that its frequency would vanish around T₃=140 K ± 10 K. This soft mode is likely to be related to a new phase transition.     

Phosphites and Hexafluoroacetone-Hexafluoroacetylacetones: a Comparison

Abstract

Selected acyclic and cyclic phosphites (RO)₂PX (1-5) were reacted with activated ketones (CF₃)₂CO (6) and Z-CF₃C(O)CH=C(OH)CF₃ (7a) / E-CF₃C(O)CH=C(OSiMe₃)CF₃ (7b) in order to study the influence of R and X on the product formation. A new type of insertion, a 1,4 group shift and cyclo-addition reactions yielding five membered rings and bicyclic fused systems were observed. In most cases phosphonates and their λ⁵[sgrave]⁵ P derivatives were obtained. The ketones in question can be considered versatile reactants in phosphorus chemistry.     

Carbamate Series of Juvenoids: Variation of the O-alkyl substituent

By changing the O-alkyl substituents of the carbamate moiety of alkyl N-{2-{4-[(2-oxocyclohexyl)methyl]phenoxy}ethyl}carbamates and subsequent transformation of the oxo group in the cyclohexyl substituent, the juvenoids 1–20 were synthesized (Scheme). The methyl ( 1–4 ), propyl ( 9–12 ), isopropyl ( 13–16 ), and prop-2-ynylcarbamates ( 17–20 ) were subjected to biological screening on several non-related insect species (Tenebrio molitor, Galleria mellonella, Dysdercus cingulatus, and Pyrrhocoris apterus). Some of the juvenoids showed high biological activity and excellent selectivity with respect to target insect species (Table 2).     

Studies in chemical ionization mass spectrometry part. XVI: Are the reactions of aliphatic cc double bonds with NO+ governed by remote functional groups?

It is shown that the characteristic fragments observed by Malosse and Einhorn (Adv. Mass Spectrom. 1369 (1986)) in the CI(NO) spectra of alkenyl acetates and related compounds (cleavage of the double bond and formation of an acyl ion), which had not been reported, for alkenes and alkenoic acids, for example, are actually formed from all straight-chain olefinic compounds (the only exceptions being where the double bond is too close to one of the ends of the chain). Their relative abundance may, however, vary from almost zero to 100%, and it is highly dependent on experimental parameters (e.g. the source temperature and even the type of instrument used). Apparent inconsistencies in the data reported in the literature could thus be resolved.     

Frequency dispersed transient absorption spectra of dissolved perylene: A case study using the density matrix version of the MCTDH method

A theoretical scheme is presented to calculate non-linear optical spectra of molecules in solution. Starting with electronic structure calculations of the ground and excited state, a subset of vibrational coordinates exhibiting the largest Huang–Rhys factors is assigned. It is used to set up a model Hamiltonian for density matrix multi configurational time-dependent Hartree (MCTDH) calculations. The expression derived for the dissipative part of the equation of motion goes beyond the earlier used Lindblad-form. In order to calculate the non-linear response the electric field strength is introduced into the density matrix equations used to directly determine the polarization. The whole scheme is applied to perylene as a reference case.