Model core potential and all-electron studies of molecules containing rare gas atoms.

Molecules HRgF (Rg = Ar, Kr, Xe, Rn) were studied at levels of theory that included electron correlation, taking relativistic effects into account either by using the recently developed parametrization of the extended model core potentials and basis sets or by using the Douglas-Kroll method with all-electron basis sets. Charge distributions were calculated according to Mulliken, Lowdin, and natural bond orbital methods of population analysis and the results of these methods were compared, confirming that bonding in these molecules corresponds to interaction between the fluoride anion and the RgH(+) moiety. In contrast to previously reported results, the present calculations show that the radon compound, HRnF, is more stable than compounds of the lighter congeners. Trends in the first ionization energies, bond lengths, energies of formation and decomposition, and harmonic vibrational frequencies were discussed and found to be consistent with the periodic trends of the atomic properties of the rare gas atoms.

Theoretical quest for photoconversion molecules having opposite directions of the electric dipole moment in S0 and S1 states.

Ab initio calculations at the level of CASPT2 with Dunning's correlation consistent cc-pVXZ (X=D, T, Q) basis sets have been carried out for pyrimidine, quinoxaline, phthalazine, and their substituted compounds to find candidates that show a change in the direction of the electric dipole moment for the S(0)-->S(1) transition. The present calculations reveal that 6,7-difluorophthalazine and 6,7-dichlorophthalazine are strong candidates having a large and clear change in the direction of the electric dipole moment on the S(0)-->S(1) transition.

Experimental and theoretical approaches toward anion-responsive tripod-lanthanide complexes: mixed-donor ligand effects on lanthanide complexation and luminescence sensing profiles.

A new series of tripods were designed to form anion-responsive, luminescent lanthanide complexes. These tripods contain pyridine, thiazole, pyrazine, or quinoline chromophores combined with amide carbonyl oxygen and tertiary nitrogen atoms. Crystallographic and EXAFS studies of the 10-coordinated tripod-La(NO(3))(3) complexes revealed that each La(3+) cation was cooperatively coordinated by one tetradentate tripod and three bidentate NO(3)(-) anions in the crystal and in CH(3)CN. Quantum chemical calculations indicated that the aromatic nitrogen plays a significant role in lanthanide complexation. The experimentally determined stability constants of complexes of the tripod with La(NO(3))(3), Eu(NO(3))(3), and Tb(NO(3))(3) were in good agreement with the theoretically calculated interaction energies. Complexation of each tripod with lanthanide triflate gave a mixture of several lanthanide complex species. Interestingly, the addition of a coordinative NO(3)(-) or Cl(-) anion to the mixture significantly influenced the lanthanide complexation profiles. The particular combination of tripod and a luminescent Eu(3+) center gave anion-selective luminescence enhancements. Pyridine-containing tripods exhibited the highest NO(3)(-) anion-selective luminescence and thus permit naked-eye detection of the NO(3)(-) anion.

Revised model core potentials of s-block elements.

We developed new model core potentials (MCPs) for s-block elements from Na to Ra, in which the outer core (n-1)s and (n-1)p electrons are treated explicitly together with the ns electrons. By adding suitable correlating functions, we demonstrated that the present MCP basis sets show excellent performance in describing the electronic structures of atoms and molecules, bringing about accurate ionization potentials of atoms and very good spectroscopic constants of ionic and covalent molecules. The results obtained with the new MCPs are very close to the ones obtained using the all-electron correlation consistent basis sets of Dunning.

Electronic structure of the GdF molecule by frozen-core four-component relativistic configuration interaction calculations.

The electronic structure of GdF is calculated based on frozen-core four-component relativistic configuration interactions. The resulting excitation energies are fairly close to experiment and correctly designate the excited states. For instance, the existence of the experimentally inferred state at 0.55 eV above the ground state is confirmed, having Omega=132 with (4f(7)5d(+) (1)6s(+) (1)); it is 0.58 eV above the ground state according to the present calculation.

Inner-valence states of N2+ and the dissociation dynamics studied by threshold photoelectron spectroscopy and configuration interaction calculation.

The N2(+) states lying in the ionization region of 26-45 eV and the dissociation dynamics are investigated by high-resolution threshold photoelectron spectroscopy and threshold photoelectron-photoion coincidence spectroscopy. The threshold photoelectron spectrum exhibits several broad bands as well as sharp peaks. The band features are assigned to the N2(+) states associated with the removal of an inner-valence electron, by a comparison with a configuration interaction calculation. In contrast, most of the sharp peaks on the threshold photoelectron spectrum are allocated to ionic Rydberg states converging to N2(2+). Dissociation products formed from the inner-valence N2(+) states are determined by threshold photoelectron-photoion coincidence spectroscopy. The dissociation dynamics of the inner-valence ionic states is discussed with reference to the potential energy curves calculated.

Relativistic correlating basis sets for lanthanide atoms from Ce to Lu.

Contracted Gaussian-type function (CGTF) sets for the description of the 4f subshell correlation and of the 6s and 5d subshell correlation are developed for lanthanide atoms from Ce to Yb. Also prepared are basis sets for the 5d orbitals, which are vacant in the ground states of most lanthanide atoms but are essential in molecular environments. In addition, correlating CGTF sets for the 4f subshell correlation are supplemented for the Lu atom. A segmented contraction scheme is employed for their compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation from accurate natural orbitals generated from configuration interaction calculations that include relativistic effects through the third-order Douglas-Kroll approximation. All-electron and model core potential calculations with the present correlating sets are performed on the ground state of the diatomic CeO molecule. The calculated spectroscopic constants are in good agreement with experimental values.

Theoretical study of the electronic structure of the lower states of the [Cr2Cl9]3- and [Mo2Cl9]3- ions.

The electronic structure of the lower states of a trigonal Cr3+ pair and Mo3+ pair, which occur in the Cs3M2Cl9 crystal (M=Cr,Mo), were studied by theoretical calculations carried out according to several methods: multireference singly and doubly excited configuration interaction, second-order configuration interaction, and multireference coupled-pair approximation. We employed a model of a [M2Cl9]3- anion embedded in a cage of point charges, which were arranged so as to simulate the anion in the crystal. The model core potential was utilized, where the relativistic effect was included for Mo. Results of the Cr complex showed that there were no direct bonds between the Cr metals. The lower electronic spectra of the [Cr2Cl9]3- ion were interpreted in terms of the electronic spectra of [CrCl6]3-. The lowest state of simultaneous excitation in both metals was considered. The [Mo2Cl9]3- ion exhibited a single direct bond between the metals. Reflecting this single bond, the observed singlet-triplet splitting was much larger than that in the case of Cr and the calculated splitting was in good agreement with the observed one. We account for the electronic spectra of the [Mo2Cl9]3- complex, which exhibited quite different features in the electronic excitation spectra in comparison with those of the Cr complex.

Compact and efficient basis sets of s- and p-block elements for model core potential method.

We propose compact and efficient valence-function sets for s- and p-block elements from Li to Rn to appropriately describe valence correlation in model core potential (MCP) calculations. The basis sets are generated by a combination of split MCP valence orbitals and correlating contracted Gaussian-type functions in a segmented form. We provide three types of basis sets. They are referred to as MCP-dzp, MCP-tzp, and MCP-qzp, since they have the quality comparable with all-electron correlation consistent basis sets, cc-pVDZ, cc-pVTZ, and cc-pVQZ, respectively, for lighter atoms. MCP calculations with the present basis sets give atomic correlation energies in good agreement with all-electron calculations. The present MCP basis sets systematically improve physical properties in atomic and molecular systems in a series of MCP-dzp, MCP-tzp, and MCP-qzp. Ionization potentials and electron affinities of halogen atoms as well as molecular spectroscopic constants calculated by the best MCP set are in good agreement with experimental values.

Relativistic correlating basis sets for the sixth-period d-block atoms from Lu to Hg.

Contracted Gaussian-type function sets to describe valence correlation are developed for the sixth-period d-block atoms Lu through Hg. A segmented contraction scheme is employed for their compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation from accurate natural orbitals generated from configuration interaction calculations, in which relativistic effects are incorporated through the third-order Douglas-Kroll approximation. The present basis sets yield more than 99% of atomic correlation energies predicted by accurate natural orbital sets of the same size. Relativistic model core potential calculations with the present correlating sets give the spectroscopic constants of the AuH molecule in excellent agreement with experimental results.

Nonadiabatic transition in the dissociation process from inner valence states of O(2) (+).

In a previous paper we reported a study of the electronic structures of inner valence states of O(2) (+) and the dissociation process, where there remained some questions as to the origins of the dissociation fragment formation of the O+((2)D)+O((3)P) limit in observed spectra. In this paper, we present the results of calculations of the nonadiabatic transition probabilities of the multichannel dissociation process from the inner valence states of O(2) (+) and reproduce the general features of observed spectra previously reported, including fragment formation, using the Zhu-Nakamura theory.

Classical trajectory calculations of intramolecular vibrational energy redistribution. I. Methanol-water complex.

Intramolecular vibrational energy redistributions of the O-H stretching (nuOH) vibration for the methanol monomer and its water complex, the methanol-water dimer, are investigated by using ab initio full-dimensional classical trajectory calculations. For the methanol monomer, in the high-energy regime of the 5nuOH overtone, the time dependence of the normal-mode energies indicates that energy flowed from the initial excited O-H stretching mode to the C-H stretching mode. This result confirms the experimental observation of energy redistribution between the O-H and C-H stretching vibrations [L. Lubich et al., Faraday Discuss. 102, 167 (1995)]. Furthermore, a lot of dynamical information in the time domain is contained in the power spectra, whose density is given by the Fourier transformation of the total momentum obtained from trajectory calculations. For the methanol-water hydrogen-bonded complex, at the high-energy level of the 5nuOH overtone, the calculated power spectrum shows considerable splitting and broadening, indicating significant energy redistribution through strong coupling between the O-H stretching vibration and other vibrations. It is thus clear that the A-H...B hydrogen-bond formation facilitates energy redistribution subsequent to the vibrational excitation of the hydrogen-bonded A-H stretching mode.

Classical trajectory calculations of intramolecular vibrational energy redistribution. II. Phenol-water complex.

Ab initio classical trajectory calculations have been applied to the intramolecular vibrational energy redistribution process of an O-H stretching vibration for phenol cation, [phenol]+, and its hydrogen-bonded water complex, [phenol-water]+. In phenol cation, a single narrow peak in the power spectrum, obtained by Fourier transformation of the autocorrelation function of its total momentum, indicates that the initial energy given to the O-H stretching oscillator of the phenol moiety is conserved and no energy flow occurs. On the other hand, for phenol-water cation, the calculated broadened power spectrum implies that the initial energy is not conserved and the energy flow causes an energy redistribution among various vibrational modes.