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Theoretical fine spectroscopy has been performed for the valence ionization spectra of furan, pyrrole, and thiophene with the symmetry-adapted-cluster configuration-interaction general-R method. The present method described that the pi(1) state interacts with the pi(3) (-2)pi*, pi(2) (-2)pi*, and pi(2) (-1)pi(3) (-1)pi* shake-up states providing the split peaks and the outer-valence satellites, both of which are in agreement with the experiments. The intensity distributions were analyzed in detail for the inner-valence region. In particular, for furan, theoretical intensities were successfully compared with the intensity measured by the electron momentum spectroscopy. The interactions of the 3b(2) and 5a(1) states with the shake-up states were remarkable for furan and pyrrole, while the 4b(2) state of thiophene had relatively large intensity.

Molecular core ionization spectra and their satellites were studied by the symmetry adapted cluster-configuration interaction (SAC-CI) general-R method. The core-electron binding energies of C, N, O, and F atoms of 22 molecules were calculated with an average deviation of 0.11 eV from the experimental values. The energy splittings between K-shell gerade and ungerade states were calculated and discussed in relation to the bond length. The satellite spectra of the C 1s and N 1s core ionizations of methane and ammonia were investigated. The SAC-CI general-R method gave many shake-up states with moderate intensities, reproducing the general feature of the experimental spectra, and thus enabling the detailed understanding and assignments of the core-electron ionization spectra., ((c) 2005 American Institute of Physics.)

Electronic structures of trans- and cis-dichloroethylenes and tetrachloroethylene were studied using symmetry-adapted cluster configuration interaction theory. Basis sets up to the aug-cc-pVTZ of Dunning, Jr., augmented with appropriate Rydberg functions were used for the calculations. The results derived in the present study show good agreement with the available experimental values. In all cases, the main bright excitation was the π→π* transition. The other vertical excitations, π→σ*, n→σ*, and n→π*, which have not been studied before, were also investigated. First Rydberg series involving transitions from the π orbitals to one 3s, three 3p, and five 3d orbitals were identified clearly. Several new assignments and reassignments of features in the experimental spectra were suggested. Contrary to earlier prediction, two n-σ* states, along with a π-σ* state in the dichloroethylenes, were calculated to be located above the main π-π* state. Accordingly, crossing between both the n-σ* states with the bright π-π* state is highly likely, unlike conclusions made in the earlier studies. This indicates that the photodissociation mechanism proposed by the earlier calculations warrants revision. Several low-lying triplet excited states were also studied. Electronic spectra of trans-1-chloro-2-fluoroethylene and cis-1-chloro-2-fluoroethylene were also calculated. The π→π* transitions of these haloethylenes are compared and interpreted in terms of the inductive and resonance effects. [ABSTRACT FROM AUTHOR]

Open-shell reference version of the symmetry-adapted cluster (SAC) and SAC-configuration-interaction (CI) methods, termed open-shell reference (OR)-SAC and OR-SAC-CI methods, are developed and applied to inner-shell ionizations of CH4, NH3, H2O, and HF. The inner-shell ionization potentials and spectra calculated by the OR-SAC and OR-SAC-CI methods are in excellent agreement with the experimental data. Including both of the electron correlation and orbital relaxation is important for quantitative agreements. Timing comparisons with the SAC-CI general-R calculations that give similar high accuracies show an efficiency of the present OR-SAC and OR-SAC-CI methods. [ABSTRACT FROM AUTHOR]

Outer- and inner-valence ionization spectra of group V hydrides, NH[sub 3], PH[sub 3], and AsH[sub 3] were studied by the symmetry-adapted-cluster configuration-interaction (SAC-CI) general-R method. Fine details of the experimental spectra of these hydrides were reproduced and the quantitative assignments of the peaks were proposed. The inner-valence satellites were classified into those including the valence or Rydberg excitations. For NH[sub 3], we interpreted the spectrum using the relative intensity and proposed some unresolved bands. For PH[sub 3], bands 2 and 3, for which different assignments have been proposed, were attributed to the [sup 2]A[sub 1] inner-valence satellites. A detailed inner-valence satellite spectrum of AsH[sub 3] is theoretically proposed. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The exponentially generated configuration interaction (EGCI) method is extended to high-spin multiplicity. This method, in which excited, ionized, and electron attached states are calculated on the basis of the correlated wave function of the ground state, is applicable to quasidegenerate states of various spin multiplicity and various number of excitation processes. The accuracy and efficiency of the EGCI method is examined for the high-spin quasidegenerate states with multiple excitation nature. Test calculations are performed for several high-spin states of C2, C2+, N2, N2+, and m-phenylenebis(methylene) (m-PBM) molecules. The EGCI method reproduces well the full-CI results in total energy, spectroscopic constants, and spin density distributions. The EGCI method is confirmed to be accurate and useful not only for investigating the energetics involved in the study of dynamics and reactions but also for studying spin density distributions of various spin multiplet states. [ABSTRACT FROM AUTHOR]

The excitation and ionization spectra of TiCl4 have been studied theoretically by the symmetry adapted cluster (SAC)/SAC-CI and multireference CI (MRD-CI) methods. The calculated spectra show good agreement with the observed spectra. The present results indicate several new assignments for the excitation spectrum. The peaks below 8.0 eV are assigned to valence excitations and those at 9.35 and 10.04 eV are assigned to Rydberg-type excitations within chlorine ligands. The ordering of the ionized states in the outer valence region is (1t1)-1 < (3t2)-1 < (1e)-1 < (2t2)-1 < (2a1)-1, which supports the result of earlier Green’s function calculations. [ABSTRACT FROM AUTHOR]

The ground and excited states of five nucleic acid bases (adenine, guanine, cytosine, uracil and thymine) were calculated by employing the SAC⁄/SAC-CI (symmetry adapted cluster/SAC configuration-interaction) method. The absorption spectra with the SAC-CI method were compared with the experimental spectra. The spectra obtained with the SAC-CI method were in good agreement with the experimental spectra in gas phase. Comparisons with the calculations with other methods were made. [ABSTRACT FROM AUTHOR]

The ground state, singlet → singlet and singlet → triplet vertical excited states of styrene have been studied by using the symmetry adapted cluster-configuration interaction (SAC-CI) method with aug-cc-pVDZ basis sets supplemented with molecule-centered Rydberg functions. The characteristic structures of the bands observed in the vacuum ultraviolet (VUV) and electron energy loss (EEL) spectra have been theoretically clarified by calculating the excitation energies, oscillator strengths, and second moments for all the excited states in the energy region 2.6–7.0 eV. The present SAC-CI theoretical results, including both the singlet → singlet and singlet → triplet vertical electronic transitions, have well reproduced the profile of the electronic spectra of styrene. Higher-energy singlet → triplet excited states and Rydberg states were extensively addressed. The valence and Rydberg configurations were found strongly mix with each other in the 61A′ and 81A′ excited states at the SAC-CI/aug-cc-pVDZ(R) level. Three main differences were found comparing with the previous CASPT2 study. (1) The 3s′- and 3p-series of Rydberg states were predicted lower than the 51A′ and 61A′ valence π–π* excited states in the SAC-CI study, whereas higher than the 51A′ and 61A′ excited states in the CASPT2 study. (2) The valence excited state (41A′) involving doubly excited configurations (4a″,4a″) → (5a″,5a″) computed at 6.08 eV at the CASPT2 level was not found in the SAC-CI calculation. (3) The characterizations (main configurations) of the 51A′ and 61A′ excited states have been found to exchange their components in the SAC-CI and CASPT2 calculations. [Copyright &y& Elsevier]

Abstract: Symmetry-adapted cluster–configuration interaction (SAC–CI) method was applied to calculate electronic CD spectrum of a nucleoside, uridine. Based on the theoretical CD and absorption spectra, the observed peaks in the experimental spectra were assigned. The excited states of uracil, the base part of uridine, were also calculated for comparison. The origin of CD rotational strength for the low-lying π–π∗ and n–π∗ excited states was analyzed. Rotational strength of the π–π∗ transition depends on the magnitude of the electric and magnetic transition dipole moments, while that of the n–π∗ originates from the angle between the two transition moments. [Copyright &y& Elsevier]