Variational quantum mechanical and active database approaches to the rotational-vibrational spectroscopy of ketene, H2CCO

A variational quantum mechanical protocol is presented for the computation of rovibrational energy levels of semirigid molecules using discrete variable representation of the Eckart-Watson Hamiltonian, a complete, "exact" inclusion of the potential energy surface, and selection of a vibrational subspace. Molecular symmetry is exploited via a symmetry-adapted Lanczos algorithm. Besides symmetry labels, zeroth-order rigid-rotor and harmonic-oscillator quantum numbers are employed to characterize the computed rovibrational states. Using the computational molecular spectroscopy algorithm presented, a large number of rovibrational states, up to J = 50, of the ground electronic state of the parent isotopologue of ketene, H(2) (12)C=(12)C=(16)O, were computed and characterized. Based on 12 references, altogether 3982 measured and assigned rovibrational transitions of H(2) (12)C=(12)C=(16)O have been collected, from which 3194 were validated. These transitions form two spectroscopic networks (SN). The ortho and the para SNs contain 2489 and 705 validated transitions and 1251 and 471 validated energy levels, respectively. The computed energy levels are compared with energy levels obtained, up to J = 41, via an inversion protocol based on this collection of validated measured rovibrational transitions. The accurate inverted energy levels allow new assignments to be proposed. Some regularities and irregularities in the rovibrational spectrum of ketene are elucidated.     

Structurally original oxathioethers macrocycles containing an exocyclic double-bond: synthesis,characterization, reactivity,and coordination

New oxathioethers macrocycles have been synthesized and characterized. Each macrocycle consists in structurally defined ether and thioether moieties and an exocyclic double-bond (2a–c) or a hydroxymethyl group (3a–c). Macrocycles (2a–c) have been synthesized by reaction of dianions of thioethers diols (1a–c) with 3-chloro-2-chloromethylprop-1-ene. Their hydroboration/oxidation led to corresponding primary alcohols (3a–c). Structures of compounds (2b) and (3a) have been determined by X-ray diffraction. The reactivity of the hydroxyl group allowed the preparation of oxathioethers macrocycles bearing a polyether chain or a benzyl group (4a,b) and the synthesis of new bicyclic sandwich-type compounds (5a,b). The ability of these functionalized macrocycles to coordinate to palladium has been investigated.     

New Halo Compounds of Si,P, As,AND Sb Bearing a Bulky Substituted Fluorenyl Group

New halo compounds of Si, P, As, and Sb, potential precursors of doubly-bonded derivatives of these elements, have been synthesized: dichloro-and difluorosilanes 2–6 bearing a methylfluorenyl group and a second substituent of various size (Me, Ph, Mes, R₂CMe); dichlorophosphines 13 and 14, fluoro- and difluoroarsines 15 and 16 and fluorostibine 17, substituted by the diphenyl (or dimesityl) phosphinofluorenyl group. Phosphine oxide and sulfide 9 and 10 also have been prepared.

     

Theoretical Investigation on the PCP(O) Linear Moiety: How to Stabilize Diphosphaallenic Derivatives

Abstract

Density functional theory calculations on phosphavinylidene(oxo)phosphorane RP?C?P(?O)R′ I are reported, where the R and R′ groups represent substituents with various electron-donor or electron-acceptor properties and different steric hindrance: H, F, Cl, OMe, SiH₃, SiMe₃, Me, Ph, Mes (2,4,6-trimethylphenyl), and Mes* (2,4,6-tri-tert-butylphenyl) and R_F 2,4,6-tris(trifluoromethyl)-phenyl. The investigations provide information about the groups that seem to be the best choice for the stabilization of such systems. The influence of the substituents’ nature on the geometrical parameters and Wiberg bond orders for the P?C bonds are discussed. Two isomers of I with a PCPO linkage (P≡C?P(?O)RR′ II and O?P?C≡PRR′ III) have also been studied.

GRAPHICAL ABSTRACT      

In silico quest for stable phosphastannaallenes

A computational study at different levels of theory was performed for the not yet synthesized phosphastannaallenes >SnCP– in order to evaluate the strength of the SnC bond, the main postulated factor to stabilize such species, and the geometry in R₂SnCPR derivatives. The influence of the substituents with various electronic effects (H, Me, Ph, F, Cl, OMe, SiMe₃) at the Sn or P atoms of the SnCP unit on the SnC bond order was evaluated in the quest for a substituent that would stabilize the phosphastannaallenic unit. PC bond orders have also been calculated.     

Eine neue Modification der Simpson'schen Methode, den Stickstoff zu bestimmen

Ohne Zusammenfassung     

Continuous monitoring of dynamical systems and master equations

We illustrate the equivalence between the non-unitary evolution of an open quantum system governed by a Markovian master equation and a process of continuous measurements involving this system. We investigate a system of two coupled modes, only one of them interacting with external degrees of freedom, represented, in the first case, by a finite number of harmonic oscillators, and, in the second, by a sequence of atoms where each one interacts with a single mode during a limited time. Two distinct regimes appear, one of them corresponding to a Zeno-like behavior in the limit of large dissipation.     

Induced Rabi oscillations and revivals in the presence of dissipation

The “time reversal” dynamics of dissipative atom-cavity systems has been recently experimentally investigated. We model the experimental procedure using semiclassical approximations which allow for analytical results and to distinguish decoherence from damping effects. We show that the basic effect of decoherence is to drastically alter the envelope of the population inversion, mainly the amplitude. Damping, on the other hand, is responsible for the anticipation of the revival times and corrections to the fast frequencies in each envelope.     

The relation between channel averages and energy averaged cross sections

For nuclear cross sections a very simple relation between channel averages and averages over incident energy is found. The assumptions used are normally satisfied for sets of channels involved in inclusive cross sections in regions without intermediate structure. In the absence of direct reactions the channel averaged cross sections are expressed in terms of channel averaged transmission coefficients; in the presence of such reactions, channel averages of first and second powers of transmission matrix elements occur when channel correlations induced by direct reactions are neglected.