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1.
Yukio Kawashima Tomohiro Hashimoto Haruyuki Nakano Kimihiko Hirao 《Theoretical chemistry accounts》1999,102(1-6):49-64
The valence π → π
* excited states of anthracene and naphthacene are studied with multireference perturbation theory with complete active space
self-consistent field reference functions. The predicted spectra provide a consistent assignment of all one- and two-photon
spectra and T-T spectra of low-lying valence π → π
* excited states of anthracene and naphthacene. The present theory predicts the valence π → π
* excitation energies with an accuracy of 0.15 eV for anthracene and of 0.25 eV or better for naphthacene. The excited states
of anthracene and naphthacene are compared with those of benzene and naphthalene studied previously. The present calculations
predict that, going from anthracene to naphthacene, there is a symmetry reversal of the two lowest singlet state transitions,
but not for the triplet, just as indicated by the experimental data. Some general trends of polyacene excited states are discussed
based on the calculated results for benzene to naphthacene. Conclusive results obtained for anthracene and naphthacene can
be used as a model for understanding the excited states of larger polyacenes.
Received: 22 April 1998 / Accepted: 6 July 1998 / Published online: 28 September 1998 相似文献
2.
3.
The repulsive ground electronic state X2Σ+ of HeH is strongly coupled to the Rydberg states at small interatomic distances. Such large couplings also occur between
some of the Rydberg states. HeH+ ions that capture an electron in a Rydberg state end up in separated He and H atoms by indirect predissociation. This paper
presents a study of potential functions and pertinent matrix elements involving the lowest electronic states: the 2Σ+ states, X, A, C, and D, and the 2Π states B and E. Individual transition rates as well as total radiative and non-radiative lifetimes have been computed for
the lowest vibrational and rotational levels.
Received: 22 June 1998 / Accepted: 21 August 1998 / Published online: 12 October 1998 相似文献
4.
The ground state and several low-lying excited states of the Mg2 dimer have been studied by means of a combination of the complete-active-space multiconfiguration self-consistent-field (CASSCF)/CAS
multireference second-order perturbation theory (CASPT2) method and coupled-cluster with single and double excitations and
perturbative contribution of connected triple excitations [CCSD(T)] scheme. Reasonably good agreement with experiment has
been obtained for the CCSD(T) ground-state potential curve but the dissociation energy of the only experimentally known A1Σ
u
+ excited state of Mg2 is somewhat overestimated at the CASSCF/CASPT2 level. The spectroscopic constants D
e, R
e and ωe deduced from the calculated potential curves for other states are also reported. In addition, some spin–orbit matrix elements
between the excited singlet and triplet states of Mg2 have been evaluated as a function of internuclear separation.
Received: 10 May 2001 / Accepted: 15 August 2001 / Published online: 30 October 2001 相似文献
5.
William T. G. Johnson David A. Hrovat Anne Skancke Weston Thatcher Borden 《Theoretical chemistry accounts》1999,102(1-6):207-225
Ab initio calculations on the lowest singlet and triplet states of 2,2-disilylcyclopentane-1,3-diyl find that the singlet
lies well below the triplet. The C
2 singlet diradical is calculated to be a minimum on the potential energy surface with an enthalpic barrier to ring closure
of ΔH
‡
298 = 13.5 kcal/mol at the CASPT2/6-31G* level of theory. The energy of the 1,3-divinyl-substituted singlet diradical is calculated
to be only 0.8 kcal/mol higher than that of 5,5-disilyl-1,3-divinylbicyclo[2.1.0]pentane at this level of theory, but the
transition state for their equilibration is computed to be 12.8 kcal/mol above the diradical in energy.
Received: 2 July 1998 / Accepted: 4 August 1998 / Published online: 16 November 1998 相似文献
6.
《Chemical physics letters》2001,331(1-2):155-164
The low-lying singlet excited states of CH2BrCl have been calculated using multiconfigurational CASSCF, second-order perturbation theory CASPT2 and its multistate extension MS-CASPT2. The CASSCF method shows spurious valence–Rydberg mixing and a wrong order of states. Inclusion of dynamical correlation by single root CASPT2 lowers dramatically the energy of the valences states but does not lead to a complete separation between valence and Rydberg states. This situation is improved by the MS-CASPT2 calculations, which gives two valence states for both A′ and A″ symmetries below the lowest Rydberg state, corresponding to n(Br)→σ*(C–Br) and n(Cl)→σ*(C–Cl) transitions at 6.1 eV (203 nm) and 7.2 eV (173 nm), and being repulsive along C–Br and C–Cl coordinates. 相似文献
7.
An all-valence-electron CI treatment is reported for the low-lying valence and Rydberg states of butadiene. All singly- and doubly-excited configurations relative to a series of the leading terms in a given CI expansion are taken into account, with resulting secular equation orders of as high as 150 000. The agreement between calculated and experimental transition energies is invariably better than 0.2 eV where comparison is possible, with all low-lying valence triplet and Rydberg singlet excited states being unambiguously assigned. The valence-shell excitation to the 2 1Ag species is concluded to correspond to the 7.06 eV band system, while the forbidden singlet—singlet transition reported by McDiarmid is assigned as x2 → 3s. The possibility of an avoided crossing between Rydberg valence 1Bu excited states having a determining influence on the appearance of the broad intense V1—N absorption is also discussed. 相似文献
8.
M. Ehara P. Tomasello J. Hasegawa H. Nakatsuji 《Theoretical chemistry accounts》1999,102(1-6):161-164
The valence ionization spectrum of HCl is studied by symmetry-adapted-cluster configuration-interaction general-R and SD-R methods. The general-R method describes well the peak positions and intensities of seven satellite lines observed below the double ionization threshold.
The twinning shake-up states due to the (4σ)−1 state and the Rydberg states of HCl+ are correctly reproduced.
Received: 26 June 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999 相似文献
9.
Tatiana Korona Bogumil Jeziorski Robert Moszynski Geerd H. F. Diercksen 《Theoretical chemistry accounts》1999,101(4):282-291
Symmetry-adapted perturbation theory is extended to the (quasi) degenerate, open-shell case. The new formalism is tested
in calculations of the interaction energies for a helium atom in the ground state interacting with an excited hydrogen atom.
It is shown that the method gives satisfactory results if the coupling with higher Rydberg states of the dimer is small, as
is the case for the A2Σ+,B2Π,E2Π,32Π, and 12Δ states of HeH. For the C2Σ+ state convergence of the method is very slow, but it can be improved by including the n=3 states in the model space.
Received: 3 June 1998 / Accepted: 9 September 1998 / Published online: 7 December 1998 相似文献
10.
R. González-Luque M. Merchán B. O. Roos 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(3-4):311-316
The electronic spectrum of cyclopropene has been studied using multiconfigurational second-order perturbation theory (CASPT2) with extended ANO-type basis sets. The calculation comprises two valence states and the 3s, 3p, 3d members of the Rydberg series converging to the π and σ ionization limits. A total of twenty singlet and twenty triplet excited states have been analyzed. The results confirm the valence nature of the lowest energy singlet-singlet band and yield a conclusive assignment: the first dipole-allowed transition in cyclcopropene is due to absorption to a (σ → π*) state. The (π → π*) (V) state is interleaved among a number of Rydberg states in the most intense band of the system. The remaining spectral bands are due to Rydberg transitions of higher energy. The two lowest singlet-triplet transitions involve the same valence states. The results are in agreement with available experimental data and provide a number of new assignments of the experimental spectra. 相似文献
11.
Adiabatic potential curves for the ground state and several low-lying excited states of the barium atom interacting with
Ne, Ar, Kr and Xe have been obtained from valence ab initio configuration-interaction calculations. Atomic cores are replaced
by scalar-relativistic l-dependent pseudopotentials, while core-polarization potentials are used for describing correlation contributions of the rare-gas
atoms and the Ba2+ cores. Implications of the resulting potential curves for the interpretation of experimental data are discussed, together
with first applications of the curves for calculating absorption profiles of the (6s
2)1S→(6p)1P Ba transition.
Received: 7 April 1998 / Accepted: 27 July 1998 / Published online: 12 October 1998 相似文献
12.
The reaction between triplet methylene and nitric oxide, producing the formaldiminoxy (CH2NO) radical, and the subsequent decomposition and isomerization reactions of CH2NO have been studied using ab␣initio quantum chemical techniques that include the Gaussian-2 (G2), CASSCF and CASPT2 methods.
Stationary points on the potential energy surfaces were located at MP2/6-31G(d) and CASSCF/cc-pVDZ levels of theory, while the electronic energies were determined using G2, G2(MP2), QCISD(T)/cc-pVTZ,
RCCSD(T)/cc-pVTZ and CASPT2/cc-pVTZ approaches. G2 is believed to be reliable at equilibrium geometries, but the determination
of certain transition state geometries and energies requires a MCSCF-based approach. The calculations suggest that CH2NO (2A′) forms in a barrierless reaction and could readily decompose to H+HCNO. A subsequent abstraction reaction then results in
H2+CNO. No molecular elimination channel was found. An alternative pathway is the formation of CH2ON, which readily isomerizes to CH2NO.
Received: 8 May 1998 / Accepted: 11 August / Published online: 9 October 1998 相似文献
13.
The results of large-scale valence ab initio calculations of the potential-energy curves for the ground states and several
excited states of Cd–rare gas (RG) van der Waals molecules are reported. In the calculations, Cd20+ and RG8+ cores are simulated by energy-consistent pseudopotentials, which also account for scalar-relativistic effects and spin-orbit
interaction within the valence shell. The potential energies of the Cd–RG species in the ΛS coupling scheme have been evaluated by means of ab initio complete-active-space multiconfiguration self-consistent-field
(CASSCF)/CAS multireference second-order perturbation theory (CASPT2) calculations with a total 28 valence electrons, but
the spin-orbit matrix has been computed in a reduced configuration interaction space restricted to the CASSCF level. Finally,
the Ω potential curves are obtained by diagonalization of the modified spin-orbit matrix (its diagonal elements before diagonalization
substituted by the corresponding CASPT2 eigenenergies). The calculated potential curves, especially the spectroscopic parameters
derived for the ground states and several excited states of the Cd–RG species are presented and discussed in the context of
available experimental data. The theoretical results exhibit very good agreement with experiment.
Received: 20 April 2000 / Accepted: 1 September 2000 / Published online: 21 December 2000 相似文献
14.
Two states of CO− which are expected to live longer than the well-known 2Π shape resonance are examined and the results obtained are compared with the analogous states of the isoelectronic N2
− system. The 4Σ− and 4Π states are found to be stable with respect to dissociation. The latter state is also stable with respect to single-electron
loss to its parent neutral state. The lifetime of this state is supposed to be long, but not necessarily long enough to allow
detection in a mass spectrometer.
Received: 28 May 1998 / Accepted: 23 July 1998 / Published online: 9 October 1998 相似文献
15.
The electronic vertical excitation energies for singlet and triplet valence, and Rydberg states of trans-buta-1,3-diene have been computed using ab initio multi-reference multi-root CI procedures with a [4s3p3d3f] set of Rydberg functions. Close numerical agreement between theory and experiment was found for a number of low-lying electronic states. 相似文献
16.
Seiichiro Ten-no Suehiro Iwata Sourav Pal Debashis Mukherjee 《Theoretical chemistry accounts》1999,102(1-6):252-261
Employing separate cluster ansatz in time-independent and time-dependent wave-operators, coupled-cluster (CC) response theory
is generalized to multireference (MR) expansion spaces. For state energies, this corresponds to the MR secular problem with
an arbitrary similarity-transformed effective Hamiltonian, H˜=Ω−1
HΩ. The effective Hamiltonian can be generated via size-extensive CC methods. Thus the states in MR linear response theory
(MRLRT) maintain the usual CC core-extensive properties. We have used the Gelfand unitary group basis of the spin-adapted
configurations to construct the matrix of H˜ in the MR excitation space. As a preliminary application, the CC singles and
doubles effective Hamiltonian is applied to excitation and photoionization energies of the CH+ and N2 molecules, and is compared with experimental results and results from other numerical procedures including conventional CC
linear response theory (CC-LRT), MR and full configuration interaction (MRCI and FCI) methods. The numerical results indicate
that MRLRT reproduces valence and external excited states quantitatively, combining the best features of CC-LRT and MRCI.
Received: 2 July 1998 / Accepted: 28 August 1998 / Published online: 11 November 1998 相似文献
17.
The excited states of the water molecule have been analyzed by using the extended quantum-chemical multistate CASPT2 method, namely, MS-CASPT2, in conjunction with large one-electron basis sets of atomic natural orbital type. The study includes 13 singlet and triplet excited states, both valence and 3s-, 3p-, and 3d-members of the Rydberg series converging to the lowest ionization potential and the 3s- and 3p-Rydberg members converging to the second low-lying state of the cation, 1 (2)A(1). The research has been focused on the analysis of the valence or Rydberg character of the low-lying states. The computation of the 1 (1)B(1) state of water at different geometries indicates that it has a predominant 3s-Rydberg character at the equilibrium geometry of the molecule but it becomes progressively a valence state described mainly by the one-electron 1b(1)-->4a(1) promotion, as expected from a textbook of general chemistry, upon elongation of the O-H bonds. The described valence-Rydberg mixing is established to be originated by a molecular orbital (MO) Rydbergization process, as suggested earlier by R. S. Mulliken [Acc. Chem. Res. 9, 7 (1976)]. The same phenomenon occurs also for the 1 (1)A(2) state whereas a more complex behavior has been determined for the 2 (1)A(1) state, where both MO Rydbergization and configurational mixing take place. Similar conclusions have been obtained for the triplet states of the molecule. 相似文献
18.
Laura Gagliardi Stefano Evangelisti Per-Olof Widmark Björn O. Roos 《Theoretical chemistry accounts》1997,97(1-4):136-142
The isomerization reaction of cubic N8 to the planar bicyclic structure analogous to pentalene has been investigated using multiconfigurational self-consistent
field and second-order perturbation theory (CASPT2). Comparative calculations using density functional theory have also been
performed. Five local minima on the energy surface have been found, and the transition states between each two consecutive
minima have been determined. The results show that all steps in the isomerization process, except one, can proceed via a set
of transition states with moderately high energy barriers (10–20 kcal/mol).
Received: 9 December 1996 / Accepted: 18 February 1997 相似文献
19.
The photoabsorption spectrum of but-2-yne in the range 5.5–11 eV (225–110 nm) has been recorded using a synchrotron radiation source. The spectrum is dominated by three d-type Rydberg series, converging to the first ionisation energy (IE) (π−1, 9.562 eV). Origins of the π3d members are 7.841, 7.977 and 8.018 eV, respectively. Transitions of low intensity, arising from excitation of the π3s state (origin, 6.35 eV) and two π3p Rydberg states (7.38 and 7.51 eV, respectively) have also been identified in the spectrum. Near-threshold electron energy-loss spectra reveal valence excited triplet states at about 5.2 and 5.8 eV, respectively.Electronic excitation energies for valence and Rydberg-type states have been computed using ab initio multi-reference multi-root CI methods. These studies used a triple zeta + polarisation basis set, augmented by diffuse (Rydberg) orbitals, to generate the theoretical singlet and triplet energy manifolds. The correlation of theory and experiment shows the nature of the more intense Rydberg state types, and identification of the main valence and Rydberg bands. Calculated energies for Rydberg states are close to those expected, and there is generally a good correlation between the theoretical and experimental envelopes. It was possible to generate singlet Rydberg states which relate to the 5-lowest IEs of but-2-yne; furthermore, the separation of these sequences shows that the IE order (under D3h symmetry) is: , also supported by direct calculation of the IEs by CI.The lowest valence singlet states are ππ*, optically forbidden, and calculated to lie near 7.3 and 7.6 eV. The states which contribute strongly to the observed spectrum are πσ* near 7.9 eV having excitation, followed by several ππ* and πσ* states between 10.0 and 10.5 eV; an 1E′ antisymmetric combination(2e′2e″ − 2e′2e″) is by far the strongest in intensity. A further group of symmetry-allowed valence states are calculated to lie near 12.3 and 12.9 eV. The two lowest triplet states, both of E′ symmetry (ππ*), have vertical excitation energies of 5.7 and 6.2 eV, but are strongly bent with a trans-CCCC unit (CS and C2h). The theoretical work confirms that, on intensity grounds, valence excited states do not contribute significantly to the spectrum. CI calculations of the ionic states give the ionisation energy sequence (D3h): . Adiabatic structures for the first cation, two triplets, and a singlet (C2h) were obtained; these show shortening of C–C, and lengthening of CC, in a trans-CCCC, as is found with ethyne. 相似文献