J. Jose

Bio: J. Jose is an academic researcher from Indian Institute of Technology Patna. The author has contributed to research in topics: Photoionization & Relativistic quantum chemistry. The author has an hindex of 8, co-authored 34 publications receiving 173 citations. Previous affiliations of J. Jose include Indian Institute of Technology Madras & Texas A&M University.

Relativistic effects in photoionization time delay near the Cooper minimum of noble-gas atoms

Abstract: The time delay of photoemission from noble-gas atoms is analyzed in the vicinity of a Cooper minimum, showing that the presence of the Cooper minimum in one channel has a strong effect on the time delay in other channels.

Interchannel coupling effects in the valence photoionization of SF6.

Abstract: The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u61t2g63eg4(5t1u6+1t2u6) 1t1g6 as the most likely ordering.

Cooper minima: a window on nondipole photoionization at low energy

Abstract: Photoionization of Mg 3s is studied near the Cooper minimum in dipole channels using the relativistic-random-phase approximation. While the importance of first-order nondipole effects on photoelectron angular distributions at low energies is well known, it is reported here for the first time that in the energy region near the dipole Cooper minimum, quadrupole transitions are not just important, but actually dominate the total photoionization cross section. Studies of dipole?dipole, dipole?quadrupole and quadrupole?quadrupole interference terms in the photoelectron angular distribution show that in the region of dipole Cooper minimum even the calculation of the dipole angular distribution parameter, ?, requires the inclusion of quadrupole channels. The significance of second-order [O(k2r2)] nondipole terms, primarily due to the contributions from electric quadrupole?quadrupole interference terms at photon energy as low as ~11 eV, are shown to induce dramatic changes in the photoelectron angular distribution over a small energy range.

Electronic structure and dynamics of confined atoms

Abstract: Confined atomic systems are of great importance owing a multitude of possible applications in various areas of science and technology. Of particular interest are atoms encaged in the $$\hbox {C}_{{60}}$$ molecule, $$\hbox {A}@\hbox {C}_{{60}}$$ , since the near-spherical symmetry of $$\hbox {C}_{{60}}$$ simplifies theoretical studies, and the stability of $$\hbox {C}_{{60}}$$ renders it amenable to experimental examination. A review of investigations of the electronic structure and dynamics of $$\hbox {A}@\hbox {C}_{{60}}$$ is presented in this manuscript focusing on developments in the last decade. Addressed mainly are how the confinement affects electronic structure properties such as ionization potentials, localization of atomic electrons, Shannon entropy, correlation effects, relativistic interactions, and others. In the area of dynamics, photoionization and e- $$\hbox {A}@\hbox {C}_{{60}}$$ scattering are reviewed and summarized, and the major effects of confinement on the dynamical properties, e.g., confinement resonances, hybridization, Wigner time delay, are delineated.

Attosecond Electron Dynamics in Molecules.

Abstract: Advances in attosecond science have led to a wealth of important discoveries in atomic, molecular, and solid-state physics and are progressively directing their footsteps toward problems of chemical interest. Relevant technical achievements in the generation and application of extreme-ultraviolet subfemtosecond pulses, the introduction of experimental techniques able to follow in time the electron dynamics in quantum systems, and the development of sophisticated theoretical methods for the interpretation of the outcomes of such experiments have raised a continuous growing interest in attosecond phenomena, as demonstrated by the vast literature on the subject. In this review, after introducing the physical mechanisms at the basis of attosecond pulse generation and attosecond technology and describing the theoretical tools that complement experimental research in this field, we will concentrate on the application of attosecond methods to the investigation of ultrafast processes in molecules, with emphasis i...

Photoexcitation of a Volume Plasmon in C$_{60}$ Ions

Abstract: Neutral C60 is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements for C+60, C2+60, and C3+60 ions in the 17-75 eV energy range show an additional resonance near 40 eV. Time-dependent density functional calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry.

Non-dipolar asymmetries of photoelectron angular distributions

Abstract: Current understanding of atomic photoionization phenomena is largely based on the dipole approximation of the photon/atom interaction. However, non-dipolar interactions have been predicted to strongly modify photoelectron angular distributions due to interference between dipolar and non-dipolar amplitudes. These effects have generally been ignored in experimental studies. The authors have measured the non-dipolar contributions to the Ar 1s, Kr 2s, and Kr 2p photoelectron angular distributions using 2-5 keV polarized x-rays. The non-dipolar interaction results in a forward/backward asymmetry with respect to the photon beam measured by rotating an electron spectrometer about the polarization vector with a fixed polar angle of 54.7{degrees}. This eliminates the angular dependence on the dipolar asymmetry parameter b. The non-dipolar asymmetries for different atomic subshells vary with energy in different ways; at certain energies the photoelectron intensity is enhanced in the backward direction, while at other energies the asymmetry vanishes or is enhanced in the forward direction. In all cases, the measured asymmetries are in good agreement with recent non-relativistic calculations which include interference between the electric-dipole and electric-quadrupole photoionization amplitudes.

Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation

Abstract: High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using ​SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20–26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected.

Photoionization of few electron systems: a hybrid coupled channels approach

Abstract: We present the hybrid anti-symmetrized coupled channels method for the calculation of fully differential photo-electron spectra of multi-electron atoms and small molecules interacting with strong laser fields. The method unites quantum chemical few-body electronic structure with strong-field dynamics by solving the time dependent Schrodinger equation in a fully anti-symmetrized basis composed of multi-electron states from quantum chemistry and a one-electron numerical basis. Photoelectron spectra are obtained via the time dependent surface flux (tSURFF) method. Performance and accuracy of the approach are demonstrated for spectra from the helium and beryllium atoms and the hydrogen molecule in linearly polarized laser fields at wavelengths from 21 to 400 nm. At long wavelengths, helium and the hydrogen molecule at equilibrium inter-nuclear distance can be approximated as single channel systems whereas beryllium needs a multi-channel description.