CNDO/S-CI SCF MO Study of the Lower States of Perfluoroacetic Anhydride. Singlet-Singlet and Singlet-Triplet Electronic Transitions

The CNDO/S-Cl spectral parametrization has been used to elucidate the lower electronic states of perfluoroacetic anhydride. The a2 (n*) unoccupied molecular orbital lies predominantly on the carbonyl group, while the b1 (no) is largely on the oxygen atoms. The lowest energy singlet excited state 1B2 is comprised almost entirely of the n n* configuration. Since the singlet and triplet 1B2 (no n*), 1A2 (no n*) result from a transition from molecular orbitals that are predominantly located on the oxygens to a molecular orbital containing about 80% C=O character, transitions to these states result in charge transfer from the oxygen to the carbon atom of the carbonyl group. Although the transition energies calculated in this study may not yield absolute comparisons with experimental values, it appears that the introduction of self-consistency, together with configuration interaction, leads to a fairly good interpretation of the singlet-singlet and singlet- triplet transitions. Various approximations were used to evaluate the two-center Coulomb repulsion integrals and the core Hamiltonian matrix elements

Molecular Orbital Theory of the Electronic Structure of Organic Compounds IV : A CNDO/S-CI SCF MO Study on the Lower Electronic States of Large Molecules. Singlet-triplet Transitions of Dioxodiazacycloalkanes

The semiempirical molecular orbital CNDO/S-CI spectral parameterization has been used to elucidate the lower triplet electronic states of a series of dioxodiazacycloalkanes. The 1³B₂(nₒπ*) and 1³A₂ (nₒπ*) triplet spectroscopic states involve intramolecular charge transfer from the oxygen to the carbon atom of the carbonyl group, which is supported by electron density calculations of these excited states. The solvation energy was incorporated in the calculations.Publicado on line en 2014.Facultad de Ciencias Exacta

Molecular Orbital Theory of the Electronic Structure of Organic Compounds I. Dioxodiazacycloalkanes

The stability of some heterocyclic compounds derived from the condensation of succinic and glutaric anhydrides with aliphatic diamines is compared using calculated values for the total energies. Further, some results derived from the electronic population analysis and the available experimental data are used to give information about the corresponding electronic structure. The CNDO/2 and INDO methods have been used for the calculations.Publicado on line en 2014.Facultad de Ciencias Exacta

Quadrature squeezing and information entropy squeezing in nonlinear two-level spin models

Normal squeezing, variance and entropy squeezing factors based on the Heisenberg uncertainty principle and Shannon information entropy theory, respectively, derived from the entangled states of two-mode coherent states in two-photon processes are numerically investigated through a previously developed generalized nonlinear JaynesCummings two-level spin model. Numerical simulations are performed and discussed for two two-photon model Hamiltonians in both resonant and off-resonant states of the spin system with the bimodal cavity field. © 2010 World Scientific Publishing Company.Fil: Grinberg, Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Variance squeezing and information entropy squeezing via Bloch coherent states in two-level nonlinear spin models

The nonclassical squeezing effect emerging from a nonlinear coupling model (generalized Jaynes–Cummings model) of a two-level atom interacting resonantly with a bimodal cavity field via two-photon transitions is investigated in the rotating wave approximation. Various Bloch coherent initial states (rotated states) for the atomic system are assumed, i.e., (i) ground state, (ii) excited state, and (iii) linear superposition of both states. Initially, the atomic system and the field are in a disentangled state, where the field modes are in Glauber coherent states via Poisson distribution. The model is numerically tested against simulations of time evolution of the based Heisenberg uncertainty relation variance and Shannon information entropy squeezing factors. The quantum state purity is computed for the three possible initial states and used as a criterion to get information about the entanglement of the components of the system. Analytical expression of the total density operator matrix elements at t > 0 shows, in fact, the present nonlinear model to be strongly entangled, where each of the definite initial Bloch coherent states is reduced to statistical mixtures. Thus, the present model does not preserve the modulus of the Bloch vector.Fil: Grinberg, Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Beyond the rotating wave approximation. An intensity dependent nonlinear coupling model in two-level systems

An intensity dependent nonlinear coupling model of a two-level system interacting with a bimodal cavity field via two-photon transitions is investigated in a scenario where the rotating wave approximation is lifted. The model is numerically tested against simulations of normal squeezing variance and entripy squeezing factors based on the Heisenberg uncertainty principle and Shannon information theory derived from entangled states.Fil: Grinberg, Horacio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Nonclassical effects in a highly nonlinear generalized homogeneous Dicke model

An intensity dependent nonlinear coupling model of N two-level atoms (generalized Dicke model) interacting dispersively with a bimodal cavity field via two-photon transitions is investigated in a scenario where the rotating wave approximation is assumed. The model becomes homogeneous in the sense that the spin transition frequency is the same for all atoms and the coupling constants emerging from the collective interactions of the atomic system with the cavity field depend only on the particular radiation field mode. This allows us to represent the Dicke Hamiltonian entirely in terms of the total angular momentum J. It is assumed that, initially, the atomic system and the field are in a disentangled state where the field modes are in Glauber coherent states and the atomic system is a superposition of states |JM (Dicke states). The model is numerically tested against simulations of normal squeezing variance of the field, squeezing factors based on the Heisenberg uncertainty principle, along with the statistical properties of the light leading to the possible production of nonclassical effects, such as degree of second-order coherence in the modes, degree of intermode correlation, as well as violation of the Cauchy-Schwartz inequality. Analytical expression of the total density operator matrix elements at t>0 shows the present nonlinear model to be strongly entangled, which is reflected in the time evolution of the linear entropy, where the superposition states are reduced to statistical mixtures. Thus, the present generalized Dicke model does not preserve the modulus of the Bloch vector. The computations, performed in the weak coupling and strong field limits, were conducted via second-order Dyson perturbative expansion of the time evolution operator matrix elements for the totality of the angular momentum states of the atomic system. © 2011 Elsevier Inc.Fil: Grinberg, Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin

Nonclassical effects in the second harmonic generation

The higher-order non-classical squeezing and quantum entanglement effects emerging from the second harmonic generation of the associated two-mode and two-photon Hamiltonian are investigated in the dispersive limit. The squeezed states of the field, including the normal and amplitude squared (higher-order) squeezing factors are generated in two ways, i.e., from the bosonic operators via amplitude powered quadrature variables, and through the SU(2) characterization of a passive and lossless device with two input and two output ports, which then allows one to visualize the operations of beam splitters and phase shifters as rotations of angular momentum operators in 3-space. Two criteria for inter-modal higher-order quantum entanglement and different coherent states for the two modes in the initial state are used to compute these non-classical effects. The unitary time evolution of the linear entropy computed from the partial trace of the density matrix over the secondary mode, is also used as a criterion of quantum entanglement. These approaches show, in fact, that the present model exhibits a considerable amount of this non-classical effect. The unitary time evolution of the linear entropy shows that the present nonlinear optical model does not preserve the modulus of the Bloch vector. Fil: Grinberg, Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin

Molecular Orbital Theory of the Electronic Structure of Organic Compounds III : A CNDO/S-CI SCF MO Study on the Lower Electronic States of Large Molecules. Singlet-Singlet Transitions of Dioxodiazacycloalkanes

The semiempirical molecular orbital CNDO/S-CI spectral parameterization has been used to elucidate the lower electronic states of a series of dioxodiazacycloalkanes. The a₁, b₁, and a' occupied molecular orbitals lie predominantly on the oxygen, while a₂, b₂, and a" are largerly nonbonding orbitals delocalized on the nitrogen and oxygen atoms. The two lowest unoccupied virtual orbitals are predicted to be of b₂, a₂, and a" symmetry. These orbitals are strongly localized on the C = 0 group. The resulting 1 B₂(nₒπ*) and 1 A₂(nₒπ*) spectroscopic states involve intramolecular charge transfer from the oxygen to the carbon atom of the carbonyl group, which is supported by electron density calculations of these excited states. Although the calculated transition energies may not allow for absolute comparisons with experimental values, it appears that the introduction of self-consistency together with solvation energy and configuration interaction, when the elements of the interaction matrix are properly evaluated, lead to a fairly good interpretation of the singlet-singlet transitions. The lowest energy singlet excited state calculated for each structure is comprised almost entirely of the n.π* configuration.Publicado on line en 2014.Facultad de Ciencias Exacta