Motion-induced energy shifts of a multilevel atom in a black-body radiation field

We investigate the influence of atomic uniform motion on radiative energy shifts of a multilevel atom when it interacts with black-body radiation. Our analysis reveals that the atomic energy shifts depend crucially on three factors: the temperature of black-body thermal radiation, atomic velocity, and atomic polarizability. In the low-temperature limit, the presence of atomic uniform motion always enhances the effect of the thermal field on the atomic energy shifts. However, in the high-temperature limit, the atomic uniform motion enhances the effect of the thermal field for an atom polarizable perpendicular to the atomic velocity but weakens it for an atom polarizable parallel to the atomic velocity. Our work indicates that the physical properties of atom–field coupling systems can in principle be regulated and controlled by the combined action of the thermal field and the atomic uniform motion.

Velocity effect on the stimulated transition process of a multilevel atom in a thermal bath

This paper investigates the stimulated transition process of a uniformly moving atom in interaction with a thermal bath of the quantum electromagnetic field. Using the perturbation theory, the atomic stimulated emission and absorption rates are calculated. The results indicate that the atomic transition rates depend crucially on the atomic velocity, the temperature of the thermal bath, and the atomic polarizability. As these factors change, the atomic stimulated transition processes can be enhanced or weakened at different degrees. In particular, slowly moving atoms in the thermal bath with high temperature ($$T\gg \omega _{0}$$ T ≫ ω 0 ) perceive a smaller effective temperature $$T \big ( 1-\frac{1}{10} v^{2} \big )$$ T ( 1 - 1 10 v 2 ) for the polarizability perpendicular to the atomic velocity or $$T \big ( 1-\frac{3}{10} v^{2} \big )$$ T ( 1 - 3 10 v 2 ) for the polarizability parallel to the atomic velocity. However, ultra-relativistic atoms perceive no influence of the background thermal bath. In turn, in terms of the atomic transition rates, this paper explores and examines the relativity of temperature of the quantum electromagnetic field.

Atomic polarizability: A periodic descriptor

Atomic polarizability is an essential theoretical construct to define and correlate many physicochemical properties. It exhibits periodicity and has a relationship with other periodic descriptors. Although a number of scales are available to compute atomic polarizability, the final scale is yet to be designed. In this venture, we have invoked a new empirical approach to compute the atomic polarizability of 103 elements of the periodic table, considering the conjoint action of other periodic descriptors, namely effective nuclear charge (Zeff) and absolute radii (r). The proposed approach is [Formula: see text], where “e” represents the electronic charge, Zeff is the effective nuclear charge, r is the absolute radius, and α is the polarizability. Our computed atomic polarizability follows all sine qua non of the periodicity. Our model significantly exhibits the relativistic effect too. A close agreement between our computed data and other available theoretical and experimental results demonstrates the efficacy of our proposed approach. Furthermore, we have established the polarizability equalization principle in terms of our computed data.

A New Model of Atomic Nucleophilicity Index and Its Application in the Field of QSAR

A new ansatz is suggested for computing the atomic nucleophilicity index (N) for atoms of 103 elements of the periodic table resting upon the mutual action of two periodic properties, atomic polarizability (α) and effective nuclear charge (Zeff). The effectiveness of the model is illustrated by the explicit periodic behaviour. In addition, molecular nucleophilicity (NAM) is being proposed as an arithmetic mean of the atomic nucleophilicities of the constituent atoms of the given molecule. Due to the nonexistence of a benchmark for atomic nucleophilicity, molecular nucleophilicity index is evaluated and a comparative analysis is made with the existing data as a validity test. Furthermore, computed density functional theory (DFT) based reactivity descriptor, viz. atomic nucleophilicity index, have been employed to construct a quantitative structure–activity relationship (QSAR) model, using regression analysis, to study the biological activities of testosterone derivatives.

Characterization of fluorine-centred `F...O' σ-hole interactions in the solid state

In the current study, the crystal structure of 1-(3-nitrophenyl)-2,2,2-trifluoroethanone (A1) and (E)-4-((4-fluorophenyl) diazenyl)phenol (A2) has been analyzed for the characterization of the presence of a `unique' and `rare' intermolecular C(sp3/sp2)—F...O contact, which has been observed to play a significant role in the crystal packing. Theoretical charge-density calculations have been performed to study the nature and strength associated with the existence of this intermolecular F...O contact, wherein the F atom is attached to ansp3-hybridized C atom in the case of A1 and to ansp2hybridized carbon in the case of A2. The crystal packing of the former contains two `electronically different' Csp3—F...O contacts which are present across and in between the layers of molecules. In the latter case, it is characterized by the presence of a very `short' (2.708 Å) and `highly directional' (168° at ∠C4—F1...O1 and 174° at ∠C10—O1...F1) Csp2—F...O contact. According to the Cambridge Structural Database (CSD) study, it is a rare example in molecular crystals. Topological features of F...O contacts in the solid state were compared with the gas-phase models. The two-dimensional and three-dimensional static deformation density obtained from theoretical multipole modeling confirm the presence of a charge depleted region on the F atoms. Minimization of the electrostatic repulsion between like charges are observed through subtle arrangements in the electronic environment in two of the short intermolecular F...O contacts. These contacts were investigated using inputs from pair energy decomposition analysis, Bader's quantum theory of atoms in molecules (QTAIM), Hirshfeld surface analysis, delocalization index, reduced density gradient (RDG) plot, electrostatic potential surface and distributed atomic polarizability. The intermolecular energy decomposition (PIXEL) and RDG–NCI (non-covalent interaction) analysis of the F...O contacts establish the interaction to be dispersive in nature. The mutual polarization of an O atom by fluorine andviceversaprovides real physical insights into the role of atomic polarizability in interacting atoms in molecules in crystals.