Classical and quantum chaos in molecular rotational excitation by ac electric fields

The interaction of diatomic molecules with an ac electric field is described by a periodically driven rigid rotor model Hamiltonian. Numerical studies of the classical and quantum dynamics reveal a remarkably close correspondence between classically chaotic dynamics and quantum time evolution. Unlike the periodically kicked rotor all the quasienergy states located in the (bounded) chaotic region in phase space are extended states. Expanded in the free rotor basis, their coefficients fullfill the statistical predictions for random vectors. Consequently, even in off resonance condition the probability for transfering angular momentum to the diatomic molecule is large and eventually the firstj _m excited rotational states will be “democratically” populated. The value ofj _m is determined by the bounded chaotic region in phase space. The rotational occupation probability shows an erratic behavior with fluctuations following the statistical predictions for random quantum states.     

Dyson orbitals for ionization from the ground and electronically excited states within equation-of-motion coupled-cluster formalism: theory, implementation, and examples

Implementation of Dyson orbitals for coupled-cluster and equation-of-motion coupled-cluster wave functions with single and double substitutions is described and demonstrated by examples. Both ionizations from the ground and electronically excited states are considered. Dyson orbitals are necessary for calculating electronic factors of angular distributions of photoelectrons, Compton profiles, electron momentum spectra, etc, and can be interpreted as states of the leaving electron. Formally, Dyson orbitals represent the overlap between an initial N-electron wave function and the N-1 electron wave function of the corresponding ionized system. For the ground state ionization, Dyson orbitals are often similar to the corresponding Hartree-Fock molecular orbitals (MOs); however, for ionization from electronically excited states Dyson orbitals include contributions from several MOs and their shapes are more complex. The theory is applied to calculating the Dyson orbitals for ionization of formaldehyde from the ground and electronically excited states. Partial-wave analysis is employed to compute the probabilities to find the ejected electron in different angular momentum states using the freestanding and Coulomb wave representations of the ionized electron. Rydberg states are shown to yield higher angular momentum electrons, as compared to valence states of the same symmetry. Likewise, faster photoelectrons are most likely to have higher angular momentum.     

Quantum Control of Coherent ρρ‐Electron Dynamics in Chiral Aromatic Molecules

Control of mobile π‐electrons is one of the fundamental issues in the organic optoelectronics for designing the next generation ultrafast switching devices. The optimal control simulations of coherent π‐electron rotations in (P)‐2,2’‐biphenol, which is the typical nonplanar aromatic molecule with axial chirality, were performed by taking into account two types of the control targets: one is generation of the maximum π‐angular momentum, and the other is the maintaining of the generated unidirectional angular momentum during a setting time duration. The optimal control pulse for each target is designed. The analysis of the simulation results shows that the effective maintaining of the unidirectional angular momentum can be realized by applying 2π pulse to one of the electronic excited states forming the coherent electronic state. The 2π pulse prevents the reverse rotation of the π‐electrons by dumping the excited state population to the ground state and subsequently by pumping the population back to the excited state. The present results provide a theoretical basis for the designing next generation ultrafast switching devices made by organic aromatic molecules.     

High resolution spectral analysis of 13CH3OH in the excited torsional states

In this work, we have extended our previous analysis of the Hamiltonian of 13C substituted methanol to include a large number of spectral lines involving the second excited torsional state using an improved model. The data set consisted of 2529 Fourier transform and microwave transitions with the rotational angular momentum J < or = 10, K < or = 6 and n < or = 2 (with 336 MW lines). The data set was fitted with the new Hamiltonian model to derive the molecular parameters. The results indicate that the model developed for the other methanol species (CH3OH, CH3(18)OH and CH3OD) is also valid for the C-13 substituted species. The results will allow the energy levels of the molecule to be calculated for higher torsional levels above the internal rotational barrier with improved precision and allow the analysis to be carried out for more excited torsional states.     

三原子分子振转激发态成簇现象理论研究

在只考虑弯曲振动与总角动量的耦合,而冻结伸缩振动的模型下,采用Jacobi多项式作为弯曲振动的基函数,用严格的变分法研究了H~2O分子的振转激发态的成簇现象。本文计算了H~2O分子的振转能级和函数,研究了振动激发态下转动高激发态中出现的成簇态。     

Excited states of antiaromatic systems1

SINDO1 studies were performed to optimize the geometry of excited states of some antiaromatic molecules. It is discussed how such states can exhibit aromatic character upon suitable electronic excitation. The nodal pattern of the molecular orbitals involved in the electronic excitation are used to invoke bond equilization in excited states. We have investigated singlet and triplet excited states of five-membered rings C₄H₅B, C₅H₅⁺ and C₅H₄O containing four π electrons and bicyclic systems bicyclo-(1,1,0)-butadiene, bicyclo-(2,2,0)-hexatriene and benzocylobutadiene. It is seen that in bicyclo-(2,2,0)-hexatriene, both the bicylic structure and the 1,4-diradical structure determine the equilibrium geometry.     

Angle and spin resolved Auger and photoelectron spectroscopy on Rb-layers by means of circularly polarized VUV radiation

Normal incidence circularly polarized VUV radiation with energies around 23 eV creates spin polarized photoelectrons from thick layers of Rb on Pt(111) and thus excites oriented 4p hole states. The preferential spin direction of the Auger electrons and its dependence upon the emission angle has been measured and is compared with the corresponding angular dependence of the primary photoelectron spin polarization also measured. Since the CVV Auger decay relates to as ² pair of valence electrons, the cross comparison of results for photoelectrons and Auger electrons studies the questions on whether photoemission and Auger decay occur in sequence, assuming an independent two step model, and whether the valences-electrons couple to a singlet state configuration.     

Isomorphic hamiltonian of a polyatomic system oscillating near a collinear reaction surface

The quantum mechanical isomorphic Hamiltonian of an N-atom system simulated by a linear semirigtd model is derived. Use of an extraneous angle allows one to avoid singularities in linear configurations, still taking advantage of the standard angular momentum technique.     

Molecular MC SCF calculations by direct minimization

Calculations on the H₂CO ground state and excited states at the equilibrium planar geometry, using the single excitation MC SCF method, are described for two basis sets. The results obtained by a full calculation including all the electrons are compared with those obtained by a pseudopotential version of the method including only the valence electrons. The results agree quite well both with each other and with the observed values.     

Laser induced recombination to excited states of hydrogen-like ions

We investigate the laser induced recombination of electrons to excited states of hydrogen-like ions. The time integration and averaging over incidente ^– energies are performed analytically for a model Hamiltonian, which takes into account the degeneracy of the states and possible resonant transitions to lower lying states. The range of validity of the model assumptions is determined by comparison with numerical calculations using the exact Hamiltonian. For an arrangement of merged laser, ion and electron beams we calculated the recombination yields as a function of the laser pulse energy to then=5 to 20 states of hydrogen like ions with nuclear charges fromZ=1 to 4.     

Hydrogenic model for stark angular momentum transfer in rydberg atoms

A model for Δn = 0 angular momentum transfer due to electric fields is developed using rotation operators for the SO(4) invariance group of hydrogen. Time-averaged angular momentum transfer probabilities suggest increased radiative lifetimes (τ ∞ n⁴) for initial low-l atoms, due to field-induced transition to high-l states.     

Magnetic circular dichroism measurements of the magnetisation properties of matrix-isolated species having spin angular momentum only

Magnetic circular dichroism has been used for the first time to study the magnetisation properties of some matrix-isolated species. The samples chosen for measurement have one, three, five and six unpaired electrons in their ground electronic states and, nominally, no orbital angular momentum. The experimental results follow the theoretical predictions very closely, but the nature of the magnetisation function is such that it is not easy to distinguish between different combinations of g-value and total spin angular momentum.     

Radiation damage of biosystems mediated by secondary electrons: resonant precursors for uracil molecules

Calculations are presented for the energy locations and spatial structures of low-energy resonant states describing transient negative ions (TNIs) of the uracil molecule in the gas phase. The resonant states are modeled using scattering calculations of low energy electrons interacting with isolated molecules in their equilibrium geometry. The interaction forces used in this model are described in detail. Examination of the spatial densities of the excess resonant electrons for the various TNIs found by the calculations allows one to associate the metastable anions with specific features of the experimentally observed fragmentation patterns.     

Computed static potentials for AHn molecules: a scattering-orintated form

A symmetry-adapted angular momentum factorization is reported for the density functions of non-linear molecules of the AH_n type with Z_A > 1, and for the static potentials generated by their ground state electronic configurations at equilibrium geometry. Results from one-centre expanded (OCE) wavefunctions are compared with those given by multicentre expansions and the rates of convergence for the electronic and nuclear terms are examined. The usefulness of such a factorization for dealing with electron-molecule scattering is discussed and its suitability in yielding molecule—molecule interactions pointed out for cases where the electron gas model is used to compute such potential surfaces.     

Radiative and nonradiative lifetimes in excited states of Ar,Kr and Xe atoms in a neon matrix

Synchrotron radiation with its intense continuum and its excellent time structure has been exploited for time resolved luminescence spectroscopy in the solid state. By selective excitation of n = 1, n′ = 2 exciton states of Xe, Kr and Ar atoms in a neon matrix we were able to identify the emitting states involved. Lifetimes within the cascade of radiative and radiationless relaxation between excited states as well as the radiative lifetimes for transitions to the ground state have been derived from the decay curves. Energy positions and radiative lifetimes of the emitting states correspond quite well with those of the free atoms. Radiative and radiationless relaxation processes take place within the manifold of excited states of the guest atoms. The rate constants for radiationless decay confirm an energy gap law. The order of the radiationless processes reaches in some cases extremely high values. Selection rules for spin and angular momentum are essential to understand the observed radiationless transition rates.     

Energy shift in (dtμ)e due to the finite size of the muonic molecular ion (dtμ)+

The energy shift due to the presence of the extended (dtμ)₁₁ pseudonucleus (in its first excited state with one unit of angular momentum) in the quasihydrogenlike system (dtμ)₁₁ e _1s is estimated using perturbation theory up to second order with two choices of zeroth order electron wavefunctions. The energy shift is found to be 0.50 meV using pure Coulomb electron wavefunctions and 0.58 meV using electron wavefunctions calculated with a potential modified to take partial account of the finite size of (dtμ)₁₁. In both cases, the perturbation Hamiltonian is expanded in multipoles, retaining terms up to and including octupole terms.     

MCD spectroscopy and magnetization studies of matrix-isolated aluminium atoms

The electronic absorption spectra and magnetic circular dichroism (MCD) spectra of matrix-isolated aluminium atoms have been studied with particular reference to the 3p4s and 3p3d transitions. The g values of the isolated atoms also have been measured via the MCD magnetization technique. It is found that, in all matrices, the orbital angular momentum of the atom is heavily quenched giving g values very near 2.0. A consistent analysis of this phenomenon and of the spectra has been developed using a model in which the surrounding noble gas atoms exert an electrostatic field upon the aluminium atom and also enter into molecular orbital formation with it. This interpretation leads to the conclusion that the spin-orbit coupling of the optical electron is negative in both ground and excited states for Al/Kr and Al/Xe, but in the excited state only for Al/Ar. These results confirm and extend the findings of earlier EPR measurements.     

Resonances in helium atoms associated with theN=4 andN=5 He+ thresholds

Some doubly excited autoionising states of helium atoms converging on theN=4 andN=5 He⁺ thresholds are calculated by use of a method of complex-coordinates. States withL≧2 and with parities of (?1) ^L and (?1) ^L+1 are calculated by using products of Slater-orbital type wave functions with expansion lengths up to 319 terms. Resonance parameters (both resonance energy and autoinoisation width) are calculated for states with angular momentum up toL=7 forN=4 resonances, andL=8 forN=5 resonances.     

Analysis of the Jahn-Teller effect in then p 2 E′ Rydberg series of H3 and D3

Spectroscopic signatures of Jahn-Teller (JT) coupling in then p _x,y ² E′ Rydberg series of H₃ and D₃ are analyzed within a simple multi-channel-quantum-defect-type model. The JT coupling constant has been inferred from existing ab initio calculations of the potential-energy surfaces of low Rydberg states of H₃. The model predicts pronounced resonant perturbations in Rydberg members with intermediaten (n=5–7) as well as strong JT-induced autoionization in absorption and ion-yield spectra from vibrationally excited initial levels. The JT-induced effects are shown to exhibit a characteristic dependence on the vibrational angular momentum of the bending mode in the initial state.