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Summary The Universe is rich with X-ray sources which can now be observed with unprecedented resolution using instruments on Chandra and XMM-Newton. In order to interpret their spectral signatures and derive reliable information regarding the physical characteristics and the dynamics of these objects and their environments, detailed spectral models have been developed which require vast amounts of...
Summary In recent years, there have been significant advances in instrumental capabilities for making X-ray spectroscopic measurements of astrophysical plasmas. There have been corresponding improvements in X-ray diagnostics for advanced multi-mega-ampere pulse power machines which produce increasingly large radiative yields from gas-puff and wire array Z pinch plasmas. Analysis used for Z pinches...
Summary Computational applications of electronic and vibrational many-body theories are increasingly indispensable in interpreting and, in some instances, predicting the spectra of gas-phase molecular species of importance in interstellar chemistry as well as in atmospheric and combustion chemistry. This chapter briefly reviews our methodological developments of electronic and vibrational many-body...
Summary We have applied multireference (MR) perturbation theory to a degenerate case using the state-specific or single root MR approach (SS-MRPT). The objective of this paper is to provide an account of the applications of both Brillouin-Wigner and Rayleigh-Schrödinger versions of the SS-MRPT with Möller-Plesset partitioning of the hamiltonian. The method is very effective to provide an accurate...
Summary Stable C–H⋯O hydrogen bonded complexes between choloroform and three small cyclic ketones (cyclohexanone, cyclopentanone, cyclobutanone) are identified by use of FTIR spectroscopy in CCl4 solution at room temperature. The C–H stretching fundamental of chloroform (νC-H) in the said three complexes exhibits blue shifting with enhancement in νC-H transition intensity. However, the red shifts...
Summary Matrix isolation infrared spectra of 1,2-cyclohexanedione (1,2-CHD) and 3-methyl-1,2-cyclohexanedione are measured in a nitrogen matrix at 8K temperature. The spectra reveal that in the matrix environment both the molecules exist exclusively in monohydroxy tautomeric forms with an intramolecular O–H⋯O=C hydrogen bonding. In the case of 3-MeCD, the fundamental of OH stretching νO−−H band appears...
Summary We consider a three state diabatic potential matrix to represent the excited states of Na3 cluster [J. Chem. Phys, 88, 6068 (1988)] at the pseudo - Jahn - Teller model situation, and analytically calculate the non - adiabatic coupling (NAC) elements and their Curls to explore the nature of the beyond Born - Oppenheimer effect on the adiabatic single surface equation. When the energy gap between...
Summary Starting from a microscopic system-reservoir Hamiltonian, we realize the damped Kubo-type oscillator and observe the non-monotonic dependence of output signal of the underdamped oscillator on the parameters of multiplicative noise.
Summary We consider an interchain interaction model to understand the spectral properties of aggregates of conjugated polymers which belong to the family of polycyclic aromatic hydrocarbons, abundant in interstellar medium. As a typical model of aggregation, we have calculated the dressed eigenstates for the equivalent and inequivalent chain-dimers with classified symmetry. The various disorder-induced...
Summary Investigation of phenomena involving parity (P) and time reversal (T) symmetry violations is of fundamental importance in physics. A few experiments to search for the P,T-odd effects have been performed on TlF and YbF molecules and considerable progress for PbO and PbF molecules is on the way. For the interpretation of the measured experimental data, it is necessary to calculate a few molecular...
Summary In recent years, there has been a significant development in the analytic derivatives of energy with respect to electric fields based on the state-of-the-art multi-reference coupled-cluster method using Lagrangian based constrained variational approach. So far, the Lagrangian based Fock space multi-reference coupled cluster (FSMRCC) method has been successfully used to calculate electrical...
Summary In this paper we report calculation of the nuclear magnetic shielding constant using extended coupled cluster response approach. We present the results for the HF, BH, CO and N2 molecules. These results show importance of correlation corrections for the shielding constant.
Summary We discuss the application of atomic physics to two diverse topics: Astrophysical opacities that determine the flow of radiation through the interior of stars, and biomedical research using nanotechnology for novel methodologies for cancer diagnostics and therapy (theranostics). Recent determination of solar abundances suggests that a re-examination of the absolute accuracy of these opacities...
Summary The nature of solar surface magnetism has been an open problem in solar physics. In this paper we address three frontline problems of spectropolarimetry of the Sun. We first review the theoretical formulation and numerical solutions of Zeeman absorption and then the Hanle scattering phenomena in ‘turbulent magnetic fields’. We show that the mean emergent Stokes profiles cannot be obtained...
Summary The method of obtaining the solution of radiative transfer equation using discrete space theory (DST) is described with (1) interaction principle for different geometries (2) star product (3) calculation of radiation field at internal points. Some of the important steps to obtain the solution of radiative transfer equation in spherical symmetry are also mentioned. Applications of DST are discussed...
Summary I first review trends in current solar spectrometry and then concentrate on comparing various spectroscopic diagnostics of the solar chromosphere. Some are actually not at all chromospheric but just photospheric or clapotispheric and do not convey information on chromospheric heating, even though this is often assumed. Balmer Hα is the principal displayer of the closed-field chromosphere,...
Summary High-resolution spectroscopy is a very important tool for studying stellar physics, perhaps, particularly so for such enigmatic objects like the R Coronae Borealis and related Hydrogen deficient stars that produce carbon dust in addition to their peculiar abundances. Examples of how high-resolution spectroscopy is used in the study of these stars to address the two major puzzles are presented:...
Summary We report preliminary results obtained from a spectroscopy and photometry campaign of the T Tauri star TW Hya in February- March, 2007. A long HETG observation with CHANDRA and simultaneous optical observations around the world have been carried out to investigate the relationship between the X-ray emission and optical variability and to connect these to the accretion and wind characteristics...
Summary The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow us to draw conclusions about details of nuclear burning and mixing processes in...
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