Extensive theoretical study on the low-lying electronic states of silicon monofluoride cation including spin-orbit coupling

Ab initio calculations on the low-lying electronic states of SiF+ are performed using the internally contracted multireference configuration interaction method with the Davidson correction and entirely uncontracted aug-cc-pV5Z basis set. The effects of spin-orbit coupling are accounted for by the state interaction approach with the full Breit-Pauli Hamiltonian. The entire 23 Omega states generated from the 12 valence Lambda-S states, which correlate with the first dissociation channel are studied for the first time. Good agreement is found between the calculated results and the available experimental data. The spin-orbit coupling effects on the potential energy curves and spectroscopic properties are studied. Various curve crossings are revealed, which could lead to the predissociation of the a3Pi, A1Pi, and (2)3Sigma+ states and the predissociation pathways are analyzed based upon the calculated spin-orbit matrix elements. The calculated ionization potentials of the ground-state SiF to a few states of SiF+ are in good agreement with the available experimental measurements. Moreover, the transition dipole moments of the dipole-allowed transitions and the transition properties for the A3Pi0+ -X1Sigma+ 0+ and B3Pi1-X1Sigma+ 0+ transitions are predicted, including the Franck-Condon factors and the radiative lifetimes.     

Extensive ab initio study of the valence and low-lying Rydberg states of BBr including spin-orbit coupling

The electronic states of the BBr molecule, including 12 valence states and 12 low-lying Rydberg states, have been studied at the theoretical level of MR-CISD+Q with all-electron aug-cc-pVQZ basis sets and Douglas-Kroll [Ann. Phys. (N.Y.) 82, 89 (1974)] scalar relativistic correction. The spin-orbit coupling effect in the valence states was calculated by the state interaction approach with the full Breit-Pauli Hamiltonian. This is the first multireference ab initio study of the excited electronic states of BBr. Potential energy curves of all states were plotted with the help of the avoided crossing rule between electronic states of the same symmetry. The structural properties of these states were analyzed. Computational results reproduced most experimental data well. The transition properties of the a (3)Pi(0(+) ), a (3)Pi(1), and A (1)Pi(1) states to the ground state X (1)Sigma(0(+) ) (+) transitions were obtained, including the transition dipole moments, the Franck-Condon factors, and the radiative lifetimes. The evaluated radiative lifetime of the a (3)Pi(0(+) ), and a (3)Pi(1) states are near 1 ms, much longer than that of the A (1)Pi(1) state.     

MRCI potential energy curves and spectroscopic constants of the ground and low-lying excited states of HgCd

The multireference configuration interaction (MRCI) electronic energy calculations with different basis sets have been performed on the ground state (X¹Σ) and three low-lying excited states (³Σ, ¹Π and ³Π) of HgCd dimer. The obtained potential energy curves (PECs) are fit to analytical potential energy functions (APEFs) using the Murrell–Sorbie potential function. Spectroscopic constants are calculated using the APEFs. Based on the PECs, the vibrational levels of each state are predicted. Our equilibrium positions of the X¹Σ state and ³Π state are in excellent agreement with the experimental reports.     

Extensive theoretical study on electronically excited states and predissociation mechanisms of sulfur monoxide including spin-orbit coupling

The potential energy curves of the 69 Ω states generated from the 24 Λ-S states of sulfur monoxide are calculated for the first time using the internally contracted multireference configuration interaction method with the Davidson correction and the entirely uncontracted aug-cc-pV5Z basis set. Spin-orbit coupling is taken into account by the state interaction approach with the full Breit-Pauli Hamiltonian. Very good agreement is achieved between our computed spectroscopic properties and the available experimental data. The transition properties of the B(3)Σ(-) -X(3)Σ(-) and (4)1-X0(+) transitions are predicted, and our computed Franck-Condon factors and radiative lifetimes match the experimental results very well. The predissociation mechanisms are investigated, and various new predissociation channels are located. We present a new interpretation on the breaking-off of the rotational levels of the B(3)Σ(-) lower vibrational states observed in experiment, and propose that the predissociation is induced by the Coriolis coupling between the B(3)Σ(-) rovibrational levels and the A(3)Π state. Our calculations indicate that, at ν' = 9, the B(3)Σ(-) state predissociates via the C(3)Π state; around ν' = 14, three spin-orbit-induced predissociation pathways via (1)(5)Σ(+) , (2)(5)Π, and e(1)Π would be open; around ν' = 17, the pathways via (2)(1)Σ(+) , (2)(3)Σ(+) and (2)(5)Σ(+) would contribute. These satisfactorily explain the experimental results about the diffuseness of the B(3)Σ(-) bands. Furthermore, various predissociation pathways of the C'(3)Π state are predicted, through which the C'(3)Π state could predissociate rapidly.     

Extensive ab initio study of the electronic states of SCl including spin-orbit coupling

The effect of different basis sets for calculation of the spectroscopic constants of the ground state of sulfur monochloride (SCl) was analyzed using scalar relativistic multireference configuration interaction with single and double excitations plus Davidson correction. Then the generally contracted all-electronic correlation-consistent polarized valence quintuple zeta basis sets were selected to compute the electronic states of SCl including 12 valence and 9 Rydberg lambda-S states. The spin-orbit coupling effect was calculated via the state interaction approach with the full Breit-Pauli Hamiltonian. This effect splits these lambda-S states into 42 omega states. Potential-energy curves of all these states are plotted with the help of the avoided crossing rule between the electronic states of the same symmetry. The structural properties of these states are analyzed. Spectroscopic constants of bound excited states that have never been observed in experiment are obtained. The transition dipole moments and the Franck-Condon factors of several transitions from low-lying bound excited states to the ground state were also calculated.     

CN~+分子势能函数和光谱常数的多参考组态相互作用方法研究

采用多参考组态相互作用方法和aug-cc-p V5Z基函数组计算了CN+分子11∑+,21∑+,13∑+和13Π电子态的势能曲线。利用MS势能函数拟合得到了相应的解析势能表达式。在此基础上求解CN+分子的核运动薛定谔方程,获得了全部振动和转动能级,并用Dunham系数展开式拟合出了光谱常数,与目前仅有的11∑+,21∑+态的文献报道结果进行了比较。结果可对航天尾气及工业过程光谱方法监控提供参考。     

Theoretical study on low‐lying states of HAlO+ and HOAl+ cations

Some low‐lying states of HAlO⁺ and HOAl⁺ cations have been studied using the complete‐active‐space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods with the contracted atomic natural orbital (ANO) basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and CASPT2/ANO levels. The ground and the first excited states of HAlO⁺ are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HOAl⁺ is X²Σ⁺ state. The A²Π state of HOAl⁺ has unique imaginary frequency. A bent local minimum M1 was found along the 1²A″ potential energy surface, and the A²Π state of HOAl⁺ should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HAlO bond angle. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study on the low-lying electronic states of NiH and NiAt

The low-lying electronic states of NiH and NiAt are investigated by using multireference second-order perturbation theory with relativistic effects taken into account. The potential energy curves as well as the corresponding spectroscopic constants are reported. The results are grossly in good agreement with the available experimental data and should thus be very useful for guiding future experimental measurements. A cross comparison with other nickel monohalides NiX (X = F, Cl, Br, and I) reveals that the change in the spin-orbit splittings when going from lighter to heavier ligands results more from the state interaction than from the relativistic effects of the ligands.     

CCSD(T) and MRCI studies on the ground and excited states of BrOClO and ClOBrO

In this work, three forms (cis, trans and nonplanar) of ClOBrO and BrOClO were optimized at CCSD(T)/cc‐pVTZ level of theory. At the most stable forms (nonplanar form) of ClOBrO and BrOClO, the vertical excitation energies for the lowest six singlet states and two triplet states were calculated at the multireference internally contracted configuration interaction (MRCI) level of theory using cc‐pVDZ, Aug‐cc‐pVDZ, cc‐pVTZ, and Aug‐cc‐pVTZ basis sets. The scalar relativistic effect on the excited states of BrOClO and ClOBrO were estimated. In addition, the potential energy curves of the lowest six singlet states and two triplet states of BrOClO and ClOBrO, as well as BrOOCl were calculated at both MCSCF (complete active space self‐consistent field) and MRCI levels of theory using Aug‐cc‐pVDZ basis set on the active space (18e,12o) along the distances of BrO? ClO, ClO? BrO, and BrO? OCl. The results were compared among BrOOCl, ClOBrO, and BrOClO. The first singlet excited state of BrOOCl is 1.12 eV higher than that of BrOClO and 1.36 eV higher than that of ClOBrO at MRCI/cc‐pVTZ level of theory. The first triplet excited state of BrOOCl is 0.77 eV higher than that of BrOClO and 0.86 eV higher than that of ClOBrO at MRCI/cc‐pVTZ level of theory. Most of the excited states of BrOClO studied in this work are unbound states; but most of the ClOBrO and BrOOCl excited states studied in this work are weakly bound states at MRCI level of theory. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Extensive theoretical studies on the low-lying electronic states of indium monochloride cation, InCl+

The global potential energy curves for the 14 low-lying doublet and quartet Lambda-S states of InCl+ are calculated at the scalar relativistic MR-CISD+Q (multireference configuration interaction with single and double excitations, and Davidson's correction) level of theory. Spin-orbit coupling is accounted for via the state interaction approach with the full Breit-Pauli Hamiltonian, which leads to 30 Omega states. The computed spectroscopic constants of nine bound Lambda-S states and 17 bound Omega states are in good agreement with the available experimental data. The transition dipole moments and Franck-Condon factors of selected transitions are also calculated, from which the corresponding radiative lifetimes are derived.     

MRCI study on spectroscopic parameters and molecular constants of the ground state of AsP(X1Σ+) molecule

The potential energy curve (PEC) for the ground state of AsP(X¹Σ⁺) has been investigated by the highly accurate valence internally contracted multireference configuration interaction method in the Molpro2008 program package with the correlation consistent basis set. The PEC is fitted to the analytic Murrrell–Sorbie function (M–S function) from which the spectroscopic constants are determined. The present D_e, B_e, α_e, ω_eχ_e, R_e, and ω_e values are of 4.2823 eV, 0.188622 cm^?1, 0.000749 cm^?1, 1.984427 cm^?1, 2.0194 Å, and 598.60 cm^?1, respectively. In addition, by numerically solving the radial Schrödinger equation of nuclear motion in the adiabatic approximation, the total of 96 vibration states is predicted when the rotational quantum number J = 0. The complete vibration levels, classical turning points, inertial rotation, and centrifugal distortion constants are reproduced. Comparison has been made with recent theoretical and experimental data. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Ab-initio study on low-lying states of the TiSi molecule

 The electronic structure of the TiSi molecule was examined using two types of multireference single and double excitation configuration interactions with highly extended basis sets, one including valence correlation and the other including valence and core–valence correlation. A multireference coupled-pair approximation (MRCPA) was further applied to the latter. The calculations suggest a ⁵Δ ground state, and the lowest excited state is ³Π and is only slightly (0.12 eV as estimated by MRCPA) above the ground state. The spectroscopic constants of the low-lying ¹Δ, ³Δ, ¹Π, ⁵Π, and ⁷Σ⁺ states as well as the ⁵Δ ground state and the ³Π excited states were evaluated, and we found that the molecule has only a weak σ bond and that six of the eight valence electrons essentially do not contribute to the bonding. The bonding nature of TiSi in these states is discussed in comparison with the TiC molecule. Received: 7 October 2000 / Accepted: 8 January 2001 / Published online: 3 May 2001     

CASPT2 study on low‐lying states of HMgO and HOMg

The HMgO and magnesium monohydroxide (HOMg) have been reinvestigated using the complete active space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods with the contracted atomic natural orbital (ANO) basis sets. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASSCF/ANO levels. The ground and the first excited states of HMgO are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HOMg is X²Σ⁺ state. The A²Π state of HOMg has unique imaginary frequency. A bent local minimum M1 was found for the first time along the 1²A″ PES and the A²Π state of HOMg should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HMgO bond angle. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Ab initio study of low-lying electronic states of SnCl2+

Complete active space self-consistent field (CASSCF), multireference configuration interaction (MRCI), and restricted-spin coupled-cluster singles-doubles with perturbative triples [RCCSD(T)] calculations have been carried out on low-lying doublet and quartet states of SnCl2+, employing basis sets of up to aug-cc-pV5Z quality. Effects of core correlation and off-diagonal spin-orbit interaction on computed vertical ionization energies were investigated. The best theoretical estimate of the adiabatic ionization energy (including zero-point vibrational energy correction) to the X2A1 state of SnCl2+ is 10.093+/-0.010 eV. The first photoelectron band of SnCl2 has also been simulated by employing RCCSD(T)/aug-cc-pV5Z potential energy functions and including Duschinsky rotation and anharmonicity.     

MRSDCI studies of low-lying electronic states of the CF 2 + ion

Summary The equilibrium geometries, excitation energies, force constants and vibrational frequencies for four low-lying electronic statesX ² A ₁,² B ₁,² B ₂ and² A ₂ of the CF ₂ ⁺ ion have been calculated at the MRSDCI level with a double zeta plus polarization basis set. Our calculated excitation energies for these states and vibrational frequencies for the ground state are in good agreement with experimental data via photoelectron spectroscopy of the CF₂ radical (carbene). The electronic transition dipole moments, oscillator strengths for the² B ₁ X ² A ₁ and² B ₂ X ² A ₁ transitions, radiative lifetimes for the² B ₁ and² B ₂ states and the spin properties for theX ² A ₁ state are calculated based on the MRSDCI wavefunctions.     

Theoretical study on potential energy curves and spectroscopy properties of ground and low-lying excited electronic states of BrCl~

The calculations on the potential energy curves and spectroscopic constants of the ground and low-lying excited states of BrCl ,one of the important molecular ions in environment science,have been performed by using the multireference configuration interaction method at high level of theory in quantum chemistry.Through analyses of the effects of the spin-orbit coupling interaction on the elec-tronic structures and spectroscopic properties,the multiconfiguration characteristic of the X2Π ground state and low-lying excited states was established.The spin-orbit coupling splitting energy of the X2 Π ground state was calculated to be 1814 cm-1,close to the experimental value 2070 cm-1.The spin-orbit coupling splitting energy of the 2Π(Ⅱ) exited state was predicted to be 766 cm-1.The transition dipole moments and Frank-Condon factors of the 3/2(Ⅲ)-X3/2 and 1/2(Ⅲ)-1/2(I) transitions were estimated,and the radiative lifetimes of the two transitions were briefly discussed.     

The low-lying electronic states of H2CN+: a preliminary ab initio study

Ab initio molecular-orbital calculations have been carried out on the low-lying triplet and singlet electronic states of the H₂CN⁺ cation, at the SCF and Møller-Plesset levels of theory. Both triplet ³A₂ and ³B₂ electronic states have similar energies. The barriers to isomerization to the ³A″ and ³A' electronic states of HCNH⁺ are estimated. It appears that ³A₂ and ³B₂ states are stable towards both isomerization and dissociation. The results of mass spectroscopic experiments involving H₂CN⁺ are discussed.     

Li+与线性碳链HC2n-体系相互作用的理论研究

应用密度泛函理论(DFT)和多体微扰理论(MP2),对Li 与线性碳链HC2n-形成的体系HC2nLi(n=1~8,C∞v)的平衡几何构型、谐振动频率、第一绝热电离能和结合能进行了研究并计算了HC2n-与Li 之间相互作用的势能曲线。计算结果表明,Li 可与线性碳链HC2n-形成稳定的化合物HC2nLi;化合物的电离能和结合能与体系大小n之间存在非线性关系。基于计算结果,得到了体系的绝热电离能和结合能与体系大小n的解析表达式。     

Electronically excited-state properties and predissociation mechanisms of phosphorus monofluoride: a theoretical study including spin-orbit coupling

The 51 Ω states generated from the 22 Λ - S states of phosphors monofluoride have been investigated using the valence internally contracted multireference configuration interaction method with the Davidson correction and the entirely uncontracted aug-cc-pV5Z basis set. The spin-orbit coupling is computed using the state interaction approach with the Breit-Pauli Hamiltonian. Based on the calculated potential energy curves, the spectroscopic constants of the bound and quasibound Λ - S and Ω states are obtained, and very good agreement with experiment is achieved. Several quasibound states caused by avoided crossings are found. Various curve crossings and avoided crossings are revealed, and with the help of our computed spin-orbit coupling matrix elements, the predissociation mechanisms of the a(1)Δ, b(1)Σ(+), e(3)Π, g(1)Π, and (3)(3)Π states are analyzed. The intricate couplings among different electronic states are investigated. We propose that the avoided crossing between the A(3)Π(0 +) and b(1)Σ(0+) (+) states may be responsible for the fact that the A(3)Π ν' ≥ 12 vibrational levels can not be observed in experiment. The transition properties of the A(3)Π - X(3)Σ(-) transition are studied, and our computed Franck-Condon factors and radiative lifetimes match the experimental results very well.