Biomedical subjects

Nimrod Moiseyev

Publications and source records attributed to Nimrod Moiseyev.

9 recordsLinked to original sources

PubMed2006

New stable multiply charged negative atomic ions in linearly polarized superintense laser fields.

Singly charged negative atomic ions exist in the gas phase and are of fundamental importance in atomic and molecular physics. However, theoretical calculations and experimental results clearly exclude the existence of any stable doubly-negatively-charged atomic ion in the gas phase, only one electron can be added to a free atom in the gas phase. In this report, using the high-frequency Floquet theory, we predict that in a linear superintense laser field one can stabilize multiply charged negative atomic ions in the gas phase. We present self-consistent field calculations for the linear superintense laser fields needed to bind extra one and two electrons to form He-, He2-, and Li2-, with detachment energies dependent on the laser intensity and maximal values of 1.2, 0.12, and 0.13 eV, respectively. The fields and frequencies needed for binding extra electrons are within experimental reach. This method of stabilization is general and can be used to predict stability of larger multiply charged negative atomic ions.

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PubMed2006

Theory of diatomic molecules in an external electromagnetic field from first quantum mechanical principles.

We study a general problem of the translational/rotational/vibrational/electronic dynamics of a diatomic molecule exposed to an interaction with an arbitrary external electromagnetic field. The theory developed in this paper is relevant to a variety of specific applications, such as alignment or orientation of molecules by lasers, trapping of ultracold molecules in optical traps, molecular optics and interferometry, rovibrational spectroscopy of molecules in the presence of intense laser light, or generation of high order harmonics from molecules. Starting from the first quantum mechanical principles, we derive an appropriate molecular Hamiltonian suitable for description of the center of mass, rotational, vibrational, and electronic molecular motions driven by the field within the electric dipole approximation. Consequently, the concept of the Born-Oppenheimer separation between the electronic and the nuclear degrees of freedom in the presence of an electromagnetic field is introduced. Special cases of the dc/ac-field limits are then discussed separately. Finally, we consider a perturbative regime of a weak dc/ac field, and obtain simple analytic formulas for the associated Born-Oppenheimer translational/rotational/vibrational molecular Hamiltonian.

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PubMed2005

Hartree-Fock orbitals for complex-scaled configuration interaction calculation of highly excited Feshbach resonances.

We examine a complex-scaled configuration interaction [(CS)CI] for highly excited Feshbach resonances, where we study the 2s(2) resonance of helium as a test case. Sizable full-CI calculations are reduced by using a correctly defined minimum active space. We compare the convergence of the minimum active space for conventional Hartree-Fock (HF) orbitals obtained as solutions to Hermitian HF equations, to the convergence of minimum active space for complex orbitals obtained as solutions to complex-scaled HF equations. Ground-state optimized orbitals are compared to a simple modification of the HF method using the excited-state mean-field potential.

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PubMed2005

Stark and field-born resonances of an open square well in a static external electric field.

The resonance positions, widths (inverse lifetimes), and wave functions of a square-potential well in the presence of a static electric field are calculated by using the outgoing boundary conditions. Our study concentrates on the field-born states that, unlike the well-known Stark resonances, are not associated with the field-free bound states. The effect of a lower cutoff of the static field on the field-born resonance phenomena is studied. The feasibility of experiments, where the isolated long-lived and overlapping short-lived field-born resonances can be explored, is discussed.

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PubMed2004

Complex autocorrelation function and energy spectrum by classical trajectory calculations.

A quasiclassical method which enables evaluation of complex autocorrelation function from classical trajectory calculations is proposed. The method is applied for two highly excited nonlinearly coupled harmonic oscillators in regimes prevailed either by regular or chaotic classical motions. A good agreement of classical and quantum autocorrelation functions is found within short (Ehrnfest) time limit. Fourier transforms of the autocorrelation functions provide moderate resolved energy spectra, where classical and quantum results nearly coincide. The actual energy levels are obtained from approximate short-time autocorrelation functions with the help of filter diagonalization. This study is a follow up to our previous work [P. Zdanska and N. Moiseyev, J. Chem. Phys. 115, 10608 (2001)], where the complex autocorrelation has been obtained up to overall phase factors of recurrences.

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PubMed2004

Extremely narrow peaks in predissociation of sodium dimer due to rovibronic coupling.

In sodium dimer the 2 (3)Pi(g), 3 (3)Pi(g), and 4 (3)Sigma(g) (+) electronic states are coupled; the coupling of the two (3)Pi(g) states is due to vibrational motion while the nonadiabatic interaction between the (3)Sigma(g) (+) and the (3)Pi(g) states-in particular, the 3 (3)Pi(g) state-is mediated by rotational interaction. The resulting vibronic problem is studied in some detail. The bound vibrational states of the 3 (3)Pi(g) and 4 (3)Pi(g) (+) states lie in the dissociation continuum of the 2 (3)Pi(g) state and become resonances due to the prevailing nonadiabatic coupling. The resonances are calculated using the complex scaling method and the available ab initio adiabatic potential energy curves. It is demonstrated that the resonances associated with rotational nonadiabatic coupling are narrower by several orders of magnitude than those that emerge from the vibrational nonadiabatic coupling. The predissociation cross section is computed and compared with experiment.

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PubMed2003

Electromagnetic realization of orders-of-magnitude tunneling enhancement in a double well system.

We report on tunneling enhancement in a periodically perturbed double well system. The double well system was realized by a structure of two optical waveguides. The transfer of light power from one waveguide to the another as induced by the periodic variations of the waveguide geometry was investigated. Our experimental measurements show that, in the presence of periodic perturbation, this transfer of light power can be enhanced by more than 500 times. We use an analogy between electromagnetic wave optics and the quantum wave phenomena to provide an experimental support to the theoretical model of tunneling enhancement of a quantum particle, facilitated by its interaction with auxiliary quantum states.

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PubMed2003

Conical intersections and bound molecular states embedded in the continuum.

Nuclear dynamics on coupled potential surfaces can lead to bound states embedded in the continuum. For one type of conical intersection situation, an explicit proof is presented that such states exist. Non-Born-Oppenheimer effects are responsible for the binding of these states. Once the Born-Oppenheimer approximation is introduced, these states at best become resonances which decay via potential tunneling. The tunneling is completely suppressed by the coupling between the electronic states. A numerical example is given.

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PubMed2002

Controlled tunneling of cold atoms: from full suppression to strong enhancement.

Two recent experiments have demonstrated the phenomenon of dynamical tunneling of cold atoms interacting with standing electromagnetic waves. We show by quantitative calculations that one can achieve a control of the tunneling period over an orders of magnitude range by changing the frequency difference of the waves by about 10% only. In this narrow parameter region, the mechanism of the tunneling oscillations evolves from the two-state to the three-state one. Our calculations demonstrate that the change in the underlying mechanism leads to the dramatic enhancement of the dynamical tunneling. Moreover, a complete suppression of the dynamical tunneling can also be achieved in the cold atom setup.

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