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[en] The efficiency of materials developed for solar energy and technological applications depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of electronic excitations is very sensitive to molecular distortions. Vibrational nuclear motions can couple to electronic dynamics driving changes in localization. The electronic energy transfer among multiple chromophores arises from several distinct mechanisms that can give rise to experimentally measured signals. Atomistic simulations of coupled electron-vibrational dynamics can help uncover the nuclear motions directing energy flow. Through careful analysis of excited state wave function evolution and a useful fragmenting of multichromophore systems, through-bond transport and exciton hopping (through-space) mechanisms can be distinguished. Such insights are crucial in the interpretation of fluorescence anisotropy measurements and can aid materials design. Finally, this Perspective highlights the interconnected vibrational and electronic motions at the foundation of nonadiabatic dynamics where nuclear motions, including torsional rotations and bond vibrations, drive electronic transitions.
[en] The potential energy curve (PEC) of HI(X1Σ+) molecule is studied using the complete active space self-consistent field method followed by the highly accurate valence internally contracted multireference configuration interaction approach at the correlation-consistent basis sets, aug-cc-pV6Z for H and aug-cc-pV5Z-pp for I atom. Using the PEC of HI(X1Σ+), the spectroscopic parameters of three isotopes, HI(X1Σ+), DI(X1Σ+) and TI(X1Σ+), are determined in the present work. For the HI(X1Σ+), the values of D0, De, Re, ωe, ωeχe, αe and Be are 3.1551 eV, 3.2958 eV, 0.16183 nm, 2290.60 cm−1, 40.0703 cm−1, 0.1699 cm−1 and 6.4373 cm−1, respectively; for the DI (X1Σ+), the values of D0, De, Re, ωe, ωeχe, αe and Be are 3.1965 eV, 3.2967 eV, 0.16183 nm, 1626.8 cm−1, 20.8581 cm−1, 0.0611 cm−1 and 3.2468 cm−1, respectively; for the TI (X1Σ+), the values of D0, De, Re, ωe, ωeχe, αe and Be are of 3.2144 eV, 3.2967 eV, 0.16183 nm, 1334.43 cm−1, 14.0765 cm−1, 0.0338 cm−1 and 2.1850 cm−1, respectively. These results accord well with the available experimental results. With the PEC of HI(X1Σ+) molecule obtained at present, a total of 19 vibrational states are predicted for the HI, 26 for the DI, and 32 for the TI, when the rotational quantum number J is equal to zero (J = 0). For each vibrational state, vibrational level G(v), inertial rotation constant Bv and centrifugal distortion constant Dv are determined when J = 0 for the first time, which are in excellent agreement with the experimental results. (atomic and molecular physics)
[en] The study of muonic atoms has yielded a variety of data on the distribution of the nuclear charge and magnetization and on the quadrupole deformation of nuclei (Devons, 1969; Wu and Wilets, 1969; Engfer et al., 1974); and more recently, on the change in the nuclear charge distribution between different nuclear states (Backe et al., 1974). The latter gives rise to what is usually called the muonic isomer shift, which is the subject of this chapter. The particular role the muon plays in probing the nucleus is primarily due to its mass being 207 times that of an electron. Consequently, the Bohr radii of muonic orbits are smaller by this factor. Actually they are so small that in muonic atoms with heavy nuclei the muon spends most of its time inside the nucleus. Clearly, the binding energy of the muon then depends sensitively on the proton distribution in the nucleus. Analogical to the Moessbauer isomer shift, the muonic isomer shift arises from the monopole term of the electrostatic interaction between the protonic charge distribution and the charge distribution of the leptons bound to the nucleus. (Auth.)
[en] The quantum-statistical-mechanical (QSM) approach to molecular relaxation phenomena is employed to compare radiationless transitions originating from an electronic state characterized by a single minimum and double minima potential surface for a vibronically active, non-totally symmetric mode. The vibronic level dependence of the decay rates for these two cases has been investigated for both small and large energy gap transitions. It is shown that the behaviour of a molecular system is quite different for an initial state possessing a double minima potential surface as compared to the case in which the initial state possesses a single minimum. (Auth.)
[en] Highlights: • We examined the attainment of the Conical Intersection (CI) in Hipoxantine (Hx). • Charge transfer in the molecule is very important in the evolution of S0 and S1. • Aromaticity impairment and push pull systems in Hx are crucial in attaining its CI. • QTAIM offers valuable tools to study the photostability of nucleobases. We analyzed the evolution of the electron density across the S0 and S1 states potential energy curves of hypoxanthine (Hx) using the Quantum Theory of Atoms in Molecules (QTAIM). Examination of QTAIM energies and electronic populations indicates that charge transfer processes are important in the stabilization of the S1 state towards the Conical Intersection (CI) which confers to Hx its photostability. Our results point that the rise of energy of the S0 state approaching the CI is accompanied by a loss of aromaticity of hypoxanthine. Overall, the analyses presented herein give important insights on the photostability of nucleobases.
[en] We compute binding energies and root-mean-square radii for weakly bound systems of N=4 and 5 identical bosons. Ground and first excited states of an N-body system appear below the threshold for binding the system with N-1 particles. Their root-mean-square radii approach constants in the limit of weak binding. Their probability distributions are on average located in nonclassical regions of space which result in universal structures. Radii decrease with increasing particle number. The ground states for more than five particles are probably nonuniversal, whereas excited states may be universal.
[en] We discuss the discrepancy between the Cung et al. [Phys. Lett. B 68, 474 (1977)] calculation of the three-photon-annihilation contribution to the positronium ground-state energy, performed using the binding energy to regulate the infrared divergences, and the recent calculation of Adkins, Bui, and Zhu [Phys. Rev. A 37, 4071 (1988)], which used a photon mass to regulate these divergences. By using a simpler version of the binding-energy approach advocated by these authors, we confirm the value of the discrepancy they obtained. Furthermore, it is shown that the additional term needed in the binding-energy approach to produce agreement between the two methods is precisely the one required to make the binding-energy regularized amplitudes gauge invariant to all orders in the binding
[en] A perturbative expansion of the electron's Dirac Coulomb propagator around a nonrelativistic form is used to evaluate the one-loop p nonrecoil corrections to ground-state hyperfine splitting in p hydrogenic atoms. A contribution previously estimated as (α/π)(Zα)2 x (18.36 +- 5)E/sub F/ is found to be (α/π) (Zα)2 (15.10 +- 0.29)E/sub F/. Theory and experiment are compared for muonium hyperfine splitting and consequences for the fine-structure constant are discussed
[en] The geometries and relative energies of the nine lowest states of the ozone molecule have been determined in C/sub 2v/ symmetry from ab initio configuration interaction calculations in a [3s2p1d] contracted Gaussian basis. Calculations were carried out over a two-dimensional grid of points in C/sub 2v/ symmetry to locate the optimum geometrical parameters R and theta for each state. For the ground 1A1 state the calculated properties (with experimental values in parentheses) are as follows: R/sub e/=1.299 A (1.271 A), theta/sub e/=116.00 (116.80), ω1=1235 cm-1 (1110 cm-1) and ω2=707 cm-1 (705 cm-1). Of the excited states only the lowest 3B2 state is found to have an adiabatic excitation energy (0.92 eV) less than the dissociation energy (D/sub e/=1.13 eV) and hence to be a likely bound species. The 1B2 state responsible for the strong absorption in the Hartley band (4.7--5.8 eV) is stabilized by asymmetric distortions away from its equilibrium C2/sub v/ geometry (R/sub e/=1.405 A, theta/sub e/=1080); this finding suggests unequal bond lengths for this state or else purely dissociative behavior. The ring (21A1) state (R/sub e/=1.449 A, theta/sub e/=600) is found to lie 1.20 eV above the ground state, while the remaining five states have adiabatic excitation energies ranging from 1.4 to 3.6 eV. The implications for photodissociation of O3 are discussed