Electronic structure of the calcium monohydroxide radical

Effective valence shell Hamiltonian H(v) calculations are used to map out three-dimensional potential energy surfaces for the 12 lowest electronic states of the CaOH radical. Excitation energies and spectroscopic constants are compared with experiment and prior computations where available, but many previously unavailable data are provided, including excited state dipole moments and oscillator strengths. Particular attention is paid to clarify the nature of nonlinear and quasilinear excited states, Renner-Teller couplings, and state mixings. The F (2)Pi and G (2)Pi (6 (2)A(') and 8 (2)A(')) states are both found to possess nonlinear local minima, due to an avoided crossing. Attention is also focused on the characteristics of basis sets necessary in high-accuracy calculations for the CaOH radical.     

Rydberg states of small NaAr(n)* clusters

The 4s and 5s Rydberg excited states of NaAr(n)* clusters are investigated using a pseudopotential quantum-classical method. While NaAr(n) clusters in their ground state are known to be weakly bound van der Waals complexes with Na lying at the surface of the argon cluster, isomers in 4s or 5s electronically excited states of small NaAr(n)* clusters (n< or =10) are found to be stable versus dissociation. The relationship between electronic excitation and cluster geometry is analyzed as a function of cluster size. For both 4s and 5s states, the stable exciplex isomers essentially appear as sodium-centered structures with similar topologies, converging towards those of the related NaAr(n)+ positive ions when the excitation level is increased. This is consistent with a Rydberg-type picture for the electronically excited cluster, described by a central sodium ion solvated by an argon shell, and an outer diffuse electron orbiting around this NaAr(n)+ cluster core.     

Dynamic polarizabilities and Rydberg states of open shell atomic systems

Time dependent coupled Hartree-Fock (TDCHF) theory is applied to calculate frequency dependent polarizabilities, transition energies, oscillator strengths and effective quantum numbers of several excited states of the open shell ions Al, Si⁺, P²⁺, S³⁺, Cl⁴⁺, Ar⁵⁺, Cl and Ar⁺ in the ²P state within and beyond the normal dispersion region. The Roothaan formalism has been adopted to deal with the open shell problem. The excitation energies are extracted from the positions of the poles of an appropriate functional. Analytic representations of the singly excited Rydberg states have been found. The results obtained compare well with spectroscopic and other elaborate theoretical data wherever available. Inner shell excitations have been found for the first time within TDCHF theory.     

Translational spectroscopy of electron impact dissociation of HF by doppler profile measurements of Balmer-α emission

The Doppler profiles of the Balmer-α emission by electron impact on HF have been investigated through varying the electron impact energy by using an etalon-grating monochromator with a high resolving power. The spectral profiles of the Balmer-α emission consist of three components, which indicates that there are three kinds of precursors leading to H*(3) contributing to the Balmer-α emission. The average kinetic energy of H*(3) is obtained for each component. From discussions on the precursors of H*(3) and their dissociation processes, the observed profiles have been ascribed to the dissociation of Rydberg states (≈18 eV), doubly excited states (≈23 eV) and inner shell excited states (≈40 eV).     

Probing the electronic and optical properties of silica-coated quantum dots with first-principles calculations

The electronic and optical natures of silica-coated semiconductor nanocrystals (Cd(2)Te(2)@(SiO(2))(24)) have been investigated by density functional theory (DFT) and time-dependent DFT calculations. The calculated results of Cd(2)Te(2)@(SiO(2))(24) have revealed that the structural synergy effect between the Cd(2)Te(2) quantum dots (QDs) and the silica coating shell plays a dominant role in the photoelectric properties. The binding of embedded Cd(2)Te(2) to the outer silica coating shell leads to the distortion of the silica nanocage, indicating strong coupling between the QDs and silica shell. The optical features of Cd(2)Te(2) clusters and Cd(2)Te(2)@(SiO(2))(24) complexes were evaluated using the time-dependent DFT method. It is determined that the maximal absorption peak of isolated Cd(2)Te(2) in a UV-Vis absorption spectrum appears at 584 nm, which shifts to 534 nm when the Cd(2)Te(2) QDs were encapsulated by silica, in close agreement with the experimental evidence. The excited process has a direct electronic transition character from the occupied Cd(2)Te(2) states to the outer silica nanocage excited states (core → shell electronic transitions). A deep insight into silica-coated QD systems is beneficial for understanding their optical nature and the development of core/shell QDs.     

Electron momentum spectroscopy of trisubstituted amines: The valence shell orbitals of triethylamine

The ionization potentials of the valence shell orbitals (up to 40 eV) of triethylamine have been measured by means of the binary (e,2e) technique. Satellite structure, due to transitions to ionic excited states, has been observed in the outer valence shell for binding energies larger than 15 eV. The electron momentum distributions of the valence orbitals have been measured on ionization peaks corresponding to main and satellite transitions. Results are compared with SCF calculations. The electron momentum distribution of the most external orbital, formed mostly by the N 2p lone pair, is discussed in detail.     

Anab initio investigation of the inner shell excited states of the molecule Cl2

Restricted Hartree-Fock calculations of the Cl₂ molecule have been carried out to investigate the X-ray excited states below Cl 2p-electron ionization potential. Some inner shell excited states are shown to have a valence or a valence-Rydberg nature that results in a considerable intensity of the appropriate transitions in the X-ray absorption spectrum. A significant interaction among some electron configurations with a 2p vacancy is predicted.     

Charge transfer in 1.4 MeV/u Ni q+→Kr collisions,q=16−22

Cross sections for the electron transfer from neutral Kr atoms to highly charged Ni ^q+ projectiles were measured at 1.4 MeV/u. Estimates on the contributions of single and double capture into the Ni-L shell and into excited states are extracted from measured cross sections for the Ni-L x-ray emission for incoming projectileL vacancies (q≧19). The role of metastable states produced in the capture process is analysed. We find that most of the capture directly populates the Ni-L shell, and the capture into excited states seems to be dominated by two-electron capture. The electrons involved in double transfer processes seem to be strongly correlated. An increase in the low-probability non-correlated double transfer with increasing number of incomingL-vacancies is indicated by the data.     

Spectroscopy of the excited-state complex of zinc(II) with 3,3′-bis(dipyrrolylmethene)

Spectra of nonstationary transient absorption of metal bis(dipyrrolylmethene) complexes in cyclohexane and ethanol, which exhibit different photophysical and photochemical properties in these solvents, have been measured and the yields of excited triplet states have been evaluated. It has been shown that the yield of triplets is determined by the intramolecular structure and the difference in fluorescence and phototransformation yields is due to intermolecular interaction of the excited molecules with the solvation shell.     

Coupled cluster investigation on the low-lying electronic states of CuCN and CuNC and the ground state barrier to isomerization

The observation of several metal cyanides and isocyanides in interstellar space has raised much interest these molecules. Optimum molecular structures, harmonic vibrational frequencies, and dipole moments of the ground electronic states (X1Sigma+), triplet excited states, and open shell singlet excited states of CuCN and CuNC were determined using different levels of nonrelativistic and scalar relativistic (Douglas-Kroll) [Ann. Phys. 82, 89 (1979)] coupled cluster theory in conjunction with atomic natural orbital basis sets and correlation consistent basis sets. For the relativistic computations the specially contracted correlation consistent Douglas-Kroll (DK) basis sets were used. Moreover, barriers to isomerization from CuCN to CuNC were computed. The predicted structures of the X1Sigma+ state for CuCN are re(Cu-C)=1.826 A and re(C-N)=1.167 A, at the most sophisticated level of theory, the scalar relativistic DK-CCSD(T)/cc-pVQZ(DK) method. These results are in excellent agreement with the experimentally determined Cu-C bond length of 1.829 A and C-N bond distance of 1.162 A. At the same level of theory, the zero-point corrected barrier to isomerization from CuCN to CuNC is estimated to be 14.7 kcal mol(-1), and the cyanide is more stable than the isocyanide by 11.5 kcal mol(-1). For both CuCN and CuNC the 3Sigma+ state is the lowest lying excited electronic state. At the DK-CCSD/cc-pVQZ(DK) level of theory, the energetic ordering of excited states of CuCN and CuNC is X1Sigma+相似文献   

Quinoidal Oligo(9,10‐anthryl)s with Chain‐Length‐Dependent Ground States: A Balance between Aromatic Stabilization and Steric Strain Release

Quinoidal π‐conjugated polycyclic hydrocarbons have attracted intensive research interest due to their unique optical/electronic properties and possible magnetic activity, which arises from a thermally excited triplet state. However, there is still lack of fundamental understanding on the factors that determine the electronic ground states. Herein, by using quinoidal oligo(9,10‐anthryl)s, it is demonstrated that both aromatic stabilisation and steric strain release play balanced roles in determining the ground states. Oligomers with up to four anthryl units were synthesised and their ground states were investigated by electronic absorption and electron spin resonance (ESR) spectroscopy, assisted by density functional theory (DFT) calculations. The quinoidal 9,10‐anthryl dimer 1 has a closed‐shell ground state, whereas the tri‐ ( 2 ) and tetramers ( 3 ) both have an open‐shell diradical ground state with a small singlet–triplet gap. Such a difference results from competition between two driving forces: the large steric repulsion between the anthryl/phenyl units in the closed‐shell quinoidal form that drives the molecule to a flexible open‐shell diradical structure, and aromatic stabilisation due to the gain of more aromatic sextet rings in the closed‐shell form, which drives the molecule towards a contorted quinoidal structure. The ground states of these oligomers thus depend on the overall balance between these two driving forces and show chain‐length dependence.     

Expanded electronic states of the fluorine molecule

Potential curves of electronically excited states of F₂ with an expanded outer orbital have been calculated using a modified frozen core technique: The ionic core has been described with a two-determinant wave function and for the excited states a mixing of configurations with different cores has been employed. An investigation of the valence shell states of F₂ is presented and potential curves for a singly excited as well as a doubly excited V-state of ¹Σ_u⁺ symmetry have been calculated. Further a low lying two-configuration state resulting from simultaneous excitation to a valence and a Rydberg orbital is predicted.     

Allowed transitions in silicon isoelectronic ions

Dipole‐allowed transitions have been studied for the first few members of the Si isoelectronic sequence. Transition energies, oscillator strengths, transition probabilities and quantum defect values have been estimated for the low‐ and high‐lying excited states of s and d symmetries up to the principal quantum number n=7 for these 3p open shell ions from P⁺ to Cr¹⁰⁺. Time‐dependent coupled Hartree–Fock (TDCHF) theory has been utilized to calculate such transition properties. Most of the results for transition energies, oscillator strengths, and transition probabilities for higher excited states are new. The transition energies for low‐lying excited states agree well with experimental data wherever available. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Fully relativistic calculations on the potential energy surfaces of the lowest 23 states of molecular chlorine

The electronic structure and spectroscopic properties (R(e), omega(e), omega(e)x(e), beta(e), and T(e)) of the ground state and the 22 lowest excited states of chlorine molecule were studied within a four-component relativistic framework using the MOLFDIR program package. The potential energy curves of all possible 23 covalent states were calculated using relativistic complete open shell configuration interaction approach. In addition, four component multireference configuration interaction with single and double excitation calculations were performed in order to infer the effects due to dynamical correlation in vertical excitations. The calculated properties are in good agreement with the available experimental data.     

Self consistent calculation of dynamic multipole polarizabilities and excited state wave functions of open shell ions: Li sequence

A variational formulation of the Hartree–Fock–Roothaan (HFR ) theory for open shell ions in presence of time dependent perturbations is presented. The theory has been used to calculate the dynamic polarizabilities of the first three ions of the Li sequence. The polarizability values, extrapolated to zero frequency, show good shell by shell agreement with the corresponding static results. The polarizability graphs display resonance behaviour at the transition frequencies of the ions, and a study of these points leads to analytic HF wave functions for their low lying excited states. The calculated transition frequencies are in excellent accord with the experimental values. The calculated oscillator strengths for the 2s → np transitions are in reasonable agreement with the extensive multiconfiguration calculations of Weiss and the available experimental results.     

Chemically Produced Excited States

Electronically excited states of organic molecules are formed in many chemical reactions. Such chemically produced excited states are (with one exception) identical to light produced excited states, and they undergo the molecular transformations expected of such states (“photochemistry without light”). The excited states can also be used in energy transfer experiments. This review covers the generation of chemically produced excited states, the chemical reactions they undergo, and the possible role of chemically produced excited states in biology.     

Open‐Shell‐Character‐Based Molecular Design Principles: Applications to Nonlinear Optics and Singlet Fission

Open‐shell character, e. g., diradical character, is a quantum chemically well‐defined quantity in ground‐state molecular systems, which is not an observable but can quantify the degree of effective bond weakness in the chemical sense or electron correlation strength in the physical sense. Because this quantity also correlates to specific excited states, physicochemical properties concerned with those states are expected to strongly correlate to the open‐shell character. This feature enables us to open a new path to revealing the mechanism of these properties as well as to realizing new design principles for efficient functional molecular systems. This account explains the open‐shell‐character‐based molecular design principles and introduces their applications to the rational design of highly efficient nonlinear optical and singlet fission molecular systems.