CASSCF and CASPT2 studies on the structures, transition energies, and dipole moments of ground and excited states for azulene

The electronic structure of azulene molecule has been studied. We have obtained the optimized structures of ground and singlet excited states by using the complete active space self-consistent-field (CASSCF) method, and calculated vertical and 0-0 transition energies between the ground and excited states with second-order M?ller-Plesset perturbation theory (CASPT2). The CASPT2 calculations indicate that the bond-equalized C(2v) structure is more stable than the bond-alternating C(s) structure in the ground state. For a physical understanding of electronic structure change from C(2v) to C(s), we have performed the CASSCF calculations of Duschinsky matrix describing mixing of the b(2) vibrational mode between the ground (1A(1)) and the first excited (1B(2)) states based on the Kekule-crossing model. The CASPT2 0-0 transition energies are in fairly good agreement with experimental results within 0.1-0.3 eV. The CASSCF oscillator strengths between the ground and excited states are calculated and compared with experimental data. Furthermore, we have calculated the CASPT2 dipole moments of ground and excited states, which show good agreement with experimental values.     

Theoretical investigation on the electronic and geometric structure of GaN2+ and GaN4+

The electronic and geometric structures of gallium dinitride cation, GaN2+ and gallium tetranitride cation, GaN4+ were systematically studied by employing density functional theory (DFT-B3LYP) and perturbation theory (MP2, MP4) in conjunction with large basis sets, (aug-)cc-pVxZ, x = T, Q. A total of 7 structures for GaN2+ and 24 for GaN4+ were identified, corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces, and bonding mechanisms for some low-lying electronic states. The calculated dissociation energy (De) of the ground state of GaN2+, X1Sigma+, is 5.6 kcal/mol with respect to Ga+(1S) + N2(X1Sigmag+) and that of the excited state, ?3Pi, is 24.8 kcal/mol with respect to Ga+(3P) + N2(X1Sigmag+). The ground state and the first excited minimum of GaN4+ are of 1A1(C2v) and 3B1(C2v) symmetry with corresponding De of 11.0 and 43.7 kcal/mol with respect to Ga+(1S) + 2N2(X1Sigmag+) for X1A1 and Ga+(3P) + 2N2(X1Sigmag+) for 3B1.     

Theoretical study of electronic structures and spectroscopic properties of Ga3Sn, GaSn3, and their ions

Ground and excited states of mixed gallium stannide tetramers (Ga3Sn, Ga3Sn+, Ga3Sn-, GaSn3, GaSn3+, and GaSn3-) are investigated employing the complete active space self-consistent-field (CASSCF), density function theory (DFT), and the coupled-cluster single and double substitution (including triple excitations) (CCSD(T)) methods. The ground states of Ga3Sn, Ga3Sn+, and Ga3Sn- are found to be the 2A1, 3B1, and 1A1 states in C2v symmetry with a planar quadrilateral geometry, respectively. The ground states of GaSn3 and GaSn3- is predicted to be the 2A1 and 1A1 states in C2v point group with a planar quadrilateral structure, respectively, while the ground state of GaSn3+ is the 1A1 state with ideal triangular pyramid C3v geometry. Equilibrium geometries, vibrational frequencies, binding energies, electron affinities, ionization energies, and other properties of Ga3Sn and GaSn3 are computed and discussed. The anion photoelectron spectra of Ga3Sn- and GaSn3- are also predicted. It is interesting to find that the amount of charge transfer between Ga and Sn2 atoms in the 1A1 state of GaSn3+ greatly increases upon electron ionization from the 2A1 state of GaSn3, which may be caused by large geometry change. On the other hand, the results of the low-lying states of Ga3Sn and GaSn3 are compared with those of Ga3Si and GaSi3.     

Structure and properties of the low-lying electronic states of CeC(2) and CeC(2)(+)

Theoretical studies on the electronic and thermodynamic properties of several electronic states of CeC(2) and CeC(2)(+) have been carried out employing state-of-the-art single- and multireference techniques. The ground and the low-lying electronic states of these two species have been found to possess C(2v) triangular structures. A (3)B(2) state has been found to be the ground state of CeC(2) while for CeC(2)(+) (2)A(2) is the ground state. The computed electron ionization energy is in excellent agreement with experiment. The experimentally observed thermodynamic properties (dissociation and atomization energies) of reactions involving CeC(2) dissociation are corrected using the computed gas-phase properties of the molecule and the partition functions. The bent triplet and singlet state of CeC(2) exhibit large dipole moments (7.0-10.5 D) and it is consistent with the ionic character (through dative charge transfer) of the cluster in ground and excited states.     

Rovibrational spectra of LiH2+, LiHD+ and LiD2+ determined from FCI property surfaces

Full configuration interaction (FCI) has been used in conjunction with the lithium [6s5p3d1f] (Iron, M. A.; et al. Mol. Phys. 2004, 101, 1345) and hydrogen aug-cc-pVTZ basis sets to construct an 83-point potential energy surface of the 1A1 ground state of 7LiH2+. Vibrational and rovibrational wave functions of the (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+ ground states were calculated variationally using an Eckart-Watson Hamiltonian. For (7)LiD2+, rovibrational transition frequencies for K = 0, 1, 2 and J < or = 10 are within ca. 0.1% of recent experimental values (Thompson, C. D.; et al. J. Chem. Phys. 2006, 125, 044310). A 47-point FCI dipole moment surface was embedded in the rovibrational Hamiltonian to calculate vibrational and rovibrational radiative properties. At 296 K, with v < or = 4 and J < or = 4, the 2(02) <-- 3(03) rotational transition in the |001> band was found to have the greatest spectral intensity with respect to the ground electronic states of (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+. In each case, the most intense rovibrational transitions have been assigned unequivocally using the J, Ka, Kc assignment scheme.     

C2v对称性簇Ru2N2的理论计算

采用密度泛函(B3LYP)方法计算了Ru2的部分低能电子组态，得到Ru2基态的电子谱项为7Δu，平衡核间距re=0.228 nm，振动频率ωe=338 cm－1，离解能De=1.92 eV. 同时计算了具有C2v对称性的Ru2N2簇中氮的活化情况，得到了各个优化几何构型下的键参数和体系能量.计算结果表明，氮氮键的活化程度由Ru2对氮起反馈作用的轨道数目决定.一般来说，氮氮键活化越强，体系能量越高，在相同的活化程度下，自旋多重度高的体系较稳定.     

Electronic states of Ga(3)Si, GaSi(3), and their ions

The equilibrium geometries and electronic states of Ga(3)Si, GaSi(3), and their ions are investigated using the complete active space self-consistent-field (CASSCF) and DFT(B3LYP)/CCSD(T) techniques. The (2)B(1), (3)B(1), and (1)A(1) states in C(2v) symmetry with a planar quadrilateral geometry are found to be the ground states of Ga(3)Si, Ga(3)Si(+), and Ga(3)Si(-), respectively. On the other hand, the ground states of GaSi(3), GaSi(3)(-) are also predicted to undergo Jahn-Teller distortion to the (2)A' and (1)A' states in C(s) with a distorted triangular pyramid geometry, respectively, whereas that of GaSi(3)(+) is found to be the (1)A(1) state in C(3v) with symmetric triangular pyramid structure. Binding energies, electron affinities, ionization energies of Ga(3)Si and GaSi(3) are computed at the CCSD(T)/QCISD(T) level and discussed.     

Probing the structural and electronic properties of Ag(n)H(-) (n = 1-3) using photoelectron imaging and theoretical calculations

Structural and electronic properties of silver hydride cluster anions (Ag(n)H(-); n = 1-3) have been explored by combining the negative ion photoelectron imaging spectroscopy and theoretical calculations. The photoelectron spectrum of AgH(-) exhibits transitions from AgH(- 2)Σ(+) to AgH (1)Σ(+) and AgH (3)Σ(+), with the electron affinity (EA) 0.57(3) eV. For Ag(2)H(-), the only observed transition is from Ag(2)H(-) (C(∞v)) (1)Σ(+) to Ag(2)H (C(2v)) (2)A(') and the electron affinity is 2.56(5) eV. Two obvious electron bands are observed in photoelectron imaging of Ag(3)H(-), which are assigned to the transitions from Ag(3)H(-) (C(2v)-T, which means C(2v) geometry with top site hydrogen) (2)B(2) to Ag(3)H (C(2v)-T) (1)A(1) and Ag(3)H (C(2v)-T) (3)B(2). The electron affinity is determined to be 1.61(9) eV. The Ag-H stretching modes in the ground states of AgH and Ag(2)H are experimentally resolved and their frequencies are measured to be 1710(80) and 1650(100) cm(-1), respectively. Aside from the above EAs and the vibrational frequencies, the vertical detachment energies to all ground states and some excited states of Ag(n)H (n = 1-3) are also obtained. Theoretical calculations reproduce the experimental energies quite well, and the results are used to assign the geometries and electronic states for all related species.     

Systematic behavior of charge-transfer transitions and energy level variation in soft donor complexes of the trivalent lanthanides

The systematic behavior of the charge-transfer (CT) energies in mixed 2,2'-bipyridyl (bipy), N,N-diethyldithiocarbamate (Et2dtc-) complexes of the trivalent lanthanides, Ln(Et2dtc)3(bipy), is investigated to understand the electronic structure of f-element complexes containing soft donor ligands. The energies of ligand to Ln3+ CT are extremely low in this system, an effect attributed to the presence of the soft donor ligands. The lowest CT energy level for the Sm3+, Eu3+, and Yb3+ complexes falls into the visible range. In Eu(Et2dtc)(bipy), the Eu3+ ion becomes nonluminescent because the CT energy stretches below the metastable 5D0 electronic state, whereas luminescence from the CT state and the 4f13 (2)F(5/2) state are observed in the Yb compound. The variation in the energy of the lowest level CT transition for the entire Ln(Et2dtc)3(bipy) series has been evaluated using the experimentally determined CT levels of the Sm3+, Eu3+, and Yb3+ compounds based on the systematic behavior of the lanthanides, which is invariant with respect to the type of ligand. The energy difference between the ground electronic states of the lanthanide ions and the ligand-centered valence band may also be calculated from these results.     

The low-lying electronic excited states of NiCO

Highly correlated coupled cluster methods with single and double excitations (CSSD) and CCSD with perturbative triple excitations were used to predict molecular structures and harmonic vibrational frequencies for the electronic ground state X 1Sigma+, and for the 3Delta, 3Sigma+, 3Phi, 1 3Pi, 2 3Pi, 1Sigma+, 1Delta, and 1Pi excited states of NiCO. The X 1Sigma+ ground state's geometry is for the first time compared with the recently determined experimental structure. The adiabatic excitation energies, vertical excitation energies, and dissociation energies of these excited states are predicted. The importance of pi and sigma bonding for the Ni-C bond is discussed based on the structures of excited states.     

Multireference configuration interaction studies on the ground and excited states of N2O2: the potential energy curves of N2O2 along N-N distance

In this paper, the ground and excited states of N2O2 were studied at the multireference configuration interaction (MRCI) level of theory with Dunning's [J. Chem. Phys. 90, 1007 (1985); 96, 6796 (1992)] correlation consistent basis sets augo-cc-pVDZ and aug-cc-pVTZ. The geometry optimizations were performed for the ground state of N2O2. The vertical excitation energies and transition moments were calculated for the low-lying singlet states of N2O2 including the lowest three 1A1 states, two 1B1 states, one 1B2 state, and two 1A2 states at the MRCI level of theory with Dunning's correlation consistent basis sets aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ. Furthermore, for the first time, the potential energy curves were calculated at the complete active space self-consistent-field and MRCI levels of theory for as many as 12 N2O2 singlet electronic states along the N-N distance. The dissociation asymptotes of these 12 N2O2 singlet electronic states were discussed.     

Electronic states and spectroscopic properties of SiTe and SiTe+

Ab initio based configuration interaction calculations have been carried out to study the low-lying electronic states and spectroscopic properties of the heaviest nonradioactive silicon chalcogenide molecule and its monopositive ion. Spectroscopic constants and potential energy curves of states of both SiTe and SiTe+ within 5 eV are reported. The calculated dissociation energies of SiTe and SiTe+ are 4.41 and 3.52 eV, respectively. Effects of the spin-orbit coupling on the electronic spectrum of both the species are studied in detail. The spin-orbit splitting between the two components of the ground state of SiTe+ is estimated to be 1880 cm(-1). Transitions such as 0+ (II)-X1Sigma(+)0+, 0+ (III)-X1Sigma(+)0+, E1Sigma(+)0+ -X1Sigma(+)0+, and A1Pi1-X1Sigma(+)0+ are predicted to be strong in SiTe. The radiative lifetime of the A1Pi state is less than a microsecond. The X(2)2Pi(1/2)-X(1)2Pi(3/2) transition in SiTe+ is allowed due to spin-orbit mixing. However, it is weak in intensity with a partial lifetime for the X2 state of about 108 ms. The electric dipole moments of both SiTe and SiTe+ in their low-lying states are calculated. The vertical ionization energies for the ionization of the ground-state SiTe to different ionic states are also reported.     

Theoretical study of isomerization and dissociation of acetylene dication in the ground and excited electronic states

Ab initio calculations employing the configuration interaction method including Davidson's corrections for quadruple excitations have been carried out to unravel the dissociation mechanism of acetylene dication in various electronic states and to elucidate ultrafast acetylene-vinylidene isomerization recently observed experimentally. Both in the ground triplet and the lowest singlet electronic states of C2H2(2+) the proton migration barrier is shown to remain high, in the range of 50 kcal/mol. On the other hand, the barrier in the excited 2 3A" and 1 3A' states decreases to about 15 and 34 kcal/mol, respectively, indicating that the ultrafast proton migration is possible in these states, especially, in 2 3A", even at relatively low available vibrational energies. Rice-Ramsperger-Kassel-Marcus calculations of individual reaction-rate constants and product branching ratios indicate that if C2H(2)2+ dissociates from the ground triplet state, the major reaction products should be CCH+(3Sigma-)+H+ followed by CH+(3Pi)+CH+(1Sigma+) and with a minor contribution (approximately 1%) of C2H+(2A1)+C+(2P). In the lowest singlet state, C2H+(2A1)+C+(2P) are the major dissociation products at low available energies when the other channels are closed, whereas at Eint>5 eV, the CCH+(1A')+H+ products have the largest branching ratio, up to 70% and higher, that of CH+(1Sigma+)+CH+(1Sigma+) is in the range of 25%-27%, and the yield of C2H++C+ is only 2%-3%. The calculated product branching ratios at Eint approximately 17 eV are in qualitative agreement with the available experimental data. The appearance thresholds calculated for the CCH++H+, CH++CH+, and C2H++C+ products are 34.25, 35.12, and 34.55 eV. The results of calculations in the presence of strong electric field show that the field can make the vinylidene isomer unstable and the proton elimination spontaneous, but is unlikely to significantly reduce the barrier for the acetylene-vinylidene isomerization and to render the acetylene configuration unstable or metastable with respect to proton migration.     

Density functional theory and multireference configuration interaction studies on low-lying excited states of TiO2

Using density functional theory at the BPW916-311+G(3df) level, optimized geometries and energies of the lowest singlet, triplet, and quintet A(1), A(2), B(1), B(2)(C(2v)) states of the TiO(2) molecule were obtained. TiO(2) has a (1)A(1) ground state in C(2v) symmetry. Adiabatic excitation energies of the low-lying singlet and triplet states range from 2.1 to 3.0 eV. The (1,3)A(2) states optimize at bond angles of about 140 degrees , lying only 0.06 eV below linear (1,3)Delta(u), whereas (1,3)B(1) and (1,3)B(2), with bond angles of 120 degrees and 96 degrees , respectively, lie 0.3-0.4 eV below the respective (1,3)Pi(u) or (1,3)Delta(u) states. Minima with short O-O distances of approximately 1.46 A, at energies of 4.2 and 4.7 eV, were found for (1)A(1) and (3)A(1). The C(2v) minima of the lowest (1)B(1) and (3)B(1) states are saddle points, suggesting lower-energy structures in C(s) symmetry. The C(2v) quintet states start at energies of 5.7 eV. Multireference configuration interaction (MRCI) methods, employing a polarized valence triple-zeta basis set, lead to similar geometries and energies. MRCI vertical excitation energies up to 4.6 eV and oscillator strengths are given. The calculated excitation energy of 2.2 eV for (1)B(2) agrees well with 2.3 eV from a fluorescence spectrum. The vertical electron detachment energy of TiO(2) (-) is 1.5 eV, in good agreement with 1.6 eV from anion photoelectron spectroscopy. An observed second photoelectron band corresponds to (1)B(2) and/or (3)B(2), but the assignment of a third band could not be verified. Vibrational frequencies, ionization energies, electron affinities, and dissociation energies are given.     

Ab Initio Theoretical Investigation on the Geometrical and Electronic Structures of AlAun-/0 (n = 2-4) Clusters

A systematic density functional theory and wave function theory investigation on the geometrical and electronic properties of AlAu n 0/-(n=2-4) clusters has been performed in this work. AlAu n-anions prove to possess ground states of the V-shaped C2v AlAu2 - , umbrella-shaped C3v AlAu3- , and perfect tetrahedral T d AlAu4- , while their neutrals favor the V-shaped C2v AlAu2 , perfect planar triangular D3h AlAu3 , and severely distorted C s AlAu4 , respectively. Aluminum aurides appear to be analogous to the corresponding aluminum hydrides, expect C s AlAu4 . Molecular orbitals (MOs) analyses also support this conclusion. Detailed orbital analyses indicate that Au 6s makes 94-96% and Au 5d makes 6-4% contribution to the Au-based orbitals in Al-Au bonds, which is smaller than the BAu n0/- series, partially reflecting the relativistic effect of gold. The one-electron detachment energies of the anions and characteristic stretching vibrational frequencies of Al-Au bonds between 100-400 cm -1 have been calculated to facilitate future experimental characterization of these clusters.     

理论研究V2O6-的结构和电子性质

The geometrical and electronic properties of the anionic and neutral V2O6 clusters were studied with the spin unrestricted hybrid density functional B3LYP method. The calculated ground states of both clusters are different from the previous theoretical results. The ground state of V2O6- is found to be a doublet with C2v symmetry, while a doublet with D2h symmetry was previously obtained by Vyboishchikov and Sauer. For neutral V2O6, the ground state is an open-shell singlet with D2h symmetry whose energy is very close to that of the triplet state. In contrast, a closed-shell singlet with D2h symmetry was obtained by Vyboishchikov and Sauer, and Calatayud et al. found a triplet ground state with Cs symmetry. Moreover,the calculated adiabatic and vertical detachment energies of the anion cluster are in much better agreement with the experimental results of photoelectron spectroscopy than previous theoretical values.     

Electronic spectrum of the AlC(2) radical

An electronic transition of the AlC2 radical (C2v structure) has been observed using laser-induced fluorescence spectroscopy. The molecule was prepared in a supersonic expansion by ablation of an aluminum rod in the presence of acetylene gas. A spectrum was recorded in the 451-453 nm region and assigned to the C 2B2-X 2A1 system (T0 = 22,102.7 cm(-1)) based on a rotational analysis and agreement with calculated molecular parameters and excitation energies. Ab initio results obtained using couple cluster methods are in accord with previous theoretical work which concludes that ground-state AlC2 possesses a T-shaped C2v 2A1 geometry, with the linear 2Sigma+ AlCC isomer 0.70 eV higher in energy. A fit of the experimental spectrum yields rotational constants in the ground and electronically excited states that are in reasonable agreement with the calculated values: A' = 1.7093(107), B' = 0.4052(50), C' = 0.3228(49) cm(-1) for the X 2A1 state, and A' = 1.5621(137), B' = 0.4028(46), C' = 0.3201(54) cm(-1) for C 2B2. Variation in individual fluorescence lifetimes suggests that the emitting C 2B2 state undergoes rovibronic mixing with lower lying electronic states.     

Low-lying singlet and triplet electronic states of RhB

The low-lying XSigma+, a3Delta, A1Delta, b3Sigma+, B1Pi, c3Pi, C1Phi, D1Sigma+, E1Pi, d3Phi, and e3Pi electronic states of RhB have been investigated at the ab initio level, using the multistate multiconfigurational second-order perturbation (MS-CASPT2) theory, with extended atomic basis sets and inclusion of scalar relativistic effects. Among the eleven electronic states included in this work, only three (the X1Sigma+, D1Sigma+, and E1Pi states) have been investigated experimentally. Potential energy curves, spectroscopic constants, dipole moments, binding energies, and chemical bonding aspects are presented for all electronic states.     

Vibrationally resolved photoelectron spectroscopy of BO- and BO2-: a joint experimental and theoretical study

We report a photoelectron spectroscopy and computational study of two simple boron oxide species: BO- and BO2-. Vibrationally resolved photoelectron spectra are obtained at several photon energies (355, 266, 193, and 157 nm) for the 10B isotopomers, 10BO- and 10BO2-. In the spectra of 10BO-, we observe transitions to the 2Sigma+ ground state and the 2Pi excited state of 10BO at an excitation energy of 2.96 eV. The electron affinity of 10BO is measured to be 2.510+/-0.015 eV. The vibrational frequencies of the ground states of 10BO- and 10BO and the 2Pi excited state are measured to be 1725+/-40, 1935+/-30, and 1320+/-40 cm-1, respectively. For 10BO2-, we observe transitions to the 2Pig ground state and two excited states of 10BO2, 2Piu, and 2Sigmau+, at excitation energies of 2.26 and 3.04 eV, respectively. The electron affinity of 10BO2 is measured to be 4.46+/-0.03 eV and the symmetrical stretching vibrational frequency of the 2Piu excited state of 10BO2 is measured to be 980+/-30 cm-1. Both density functional and ab initio calculations are performed to elucidate the electronic structure and chemical bonding of the two boron oxide molecules. Comparisons with the isoelectronic AlO- and AlO2- species and the closely related molecules CO, N2, CN-, and CO2 are also discussed.