OH自由基的高精度量子化学研究

采用内收缩MRCI方法(Internally Contracted Multiconfiguration-Reference Configuration Interaction)研究了OH自由基, 计算得到其基态稳定构型的键长是0.09708 nm, 对应的实验值是0.096966 nm, 第一激发态的键长是0.10137 nm,实验值是0.10121 nm. 同时得到势能曲线PECs (Potential Energy Curve), 再分别由Murrell-Sorbie势能函数拟合计算和POLFIT程序计算得到OH自由基在基态X²Π和第一激发态A²Σ⁺时的光谱数据：平衡振动频率ω_e, 非谐性常数ω_eχ_e以及高阶修正ω_eY_e, 平衡转动常数B_e, 振转耦合系数α_e, 解离能D₀和垂直跃迁能量ν₀₀. 这些理论计算结果与最新的实验值非常吻合, 精确度比前人也有很大提高. 其中我们计算得到基态OH(X²Π)的解离能D₀＝35568.86 cm^－1, 第一激发态OH (A²Σ⁺)的解离能D₀＝18953.93 cm^－1, 从第一激发态A²Σ⁺ (ν＝0)到基态X²Π (v＝0)的垂直跃迁能ν₀₀＝32496.42 cm^－1.     

Ab initio spectroscopic study for the NaRb molecule in ground and excited states

A wide adiabatic study is performed for NaRb molecule, involving 15¹Σ⁺ electronic states including the ionic state Na^?Rb⁺, as well as 14³Σ⁺, 1–9^1,3Π, and 1–5^1,3Δ states. This investigation is performed using an ab initio approach which involves the effective core potential, the core polarization potential with l‐dependent cut‐off functions. The NaRb system has been treated as a two‐electron system and the full valence configuration interaction is easily achieved. The spectroscopic constants R_e, D_e, T_e, ω_e, ω_ex_e, B_e, and D₀ for all these states are derived. We have also computed the vibrational levels as well their spacing for different values of J. In addition, permanent and transition dipole moments are determined and analyzed. The Dunham coefficients have been used to perform experimental spacing to compare directly with our results. The present calculations on NaRb extend previous theoretical works to numerous electronic excited states in the various symmetries. © 2014 Wiley Periodicals, Inc.     

Theoretical study of spectroscopic and molecular properties of several low‐lying electronic states of CO molecule

The potential energy curves (PECs) of eight low‐lying electronic states (X¹Σ⁺, a³Π, a′³Σ⁺, d³Δ, e³Σ^?, A¹Π, I¹Σ^?, and D¹Δ) of the carbon monoxide molecule have been studied by an ab initio quantum chemical method. The calculations have been performed using the complete active space self‐consistent field method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation‐consistent aug‐cc‐pV5Z basis set. The effects on the PECs by the core‐valence correlation and relativistic corrections are included. The way to consider the relativistic corrections is to use the third‐order Douglas–Kroll Hamiltonian approximation at the level of a cc‐pV5Z basis set. Core‐valence correlation corrections are performed using the cc‐pCVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size‐extensivity errors by means of the Davidson modification (MRCI+Q). The spectroscopic parameters (D_e, T_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e, α_e, and γ_e) of these electronic states are calculated using these PECs. The spectroscopic parameters are compared with those reported in the literature. Using the Breit–Pauli operator, the spin–orbit coupling effect on the spectroscopic parameters is discussed for the a³Π electronic state. With the PECs obtained by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations, the complete vibrational states of each electronic state have been determined. The vibrational manifolds have been calculated for each vibrational state of each electronic state. The vibrational level G(ν), inertial rotation constant B_ν, and centrifugal distortion constant D_ν of the first 20 vibrational states when the rotational quantum number J equals zero are reported and compared with the experimental data. Comparison with the measurements demonstrates that the present spectroscopic parameters and molecular constants determined by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations are both reliable and accurate. © 2012 Wiley Periodicals, Inc.     

Theoretical calculation of the low laying electronic states of the molecular ion RbH+

Using an ab initio method, the potential energy has been calculated for the 29 lowest molecular states of symmetries ²Σ⁺, ²Π, ²Δ for the molecular ion RbH⁺. The calculation is based on nonempirical pseudopotentials and parameterized ?‐dependent polarization potentials. Gaussian basis sets have been used for both atoms. The spectroscopic constants for 18 electronic sates have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. Through the canonical functions approach the eigenvalue E_v, the abscissas of the corresponding turning points (R_min and R_max) and the rotational constants B_v have been calculated up to 24 vibrational levels for the considered bound states. The comparison of the present results with those available in literature shows a very good agreement. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

O‐loss photodissociation of the OCS+ ion in the low‐lying electronic states studied using multiconfiguration second‐order perturbation theory

The CASPT2 potential energy curves (PECs) for O‐loss dissociation from the X²Π, A²Π, B²Σ⁺, C²Σ⁺, 1⁴Σ^?, 1²Σ^?, and 1⁴Π states of the OCS⁺ ion were calculated. The PEC calculations indicate that X²Π, 1⁴Σ^?, 1²Σ^?, and 1⁴Π correlate with CS⁺(X²Σ⁺) + O(³P_g); A²Π and B²Σ⁺ correlate with CS⁺(A²Π) + O(³P_g); and C²Σ⁺ probably correlates with CS⁺(X²Σ⁺) + O(¹D_g). The CASSCF minimum energy crossing point (MECP) calculations were performed for the C²Σ⁺/1⁴Σ^?, C²Σ⁺/1⁴Π, A²Π/1⁴Σ^?, A²Π/1²Σ^?, A²Π/1⁴Π, and B²Σ⁺/1²Σ^? state pairs and the spin‐obit couplings were calculated at the located MECPs. A conical intersection point between the B²Σ⁺ and C²Σ⁺ potential energy surfaces was found at the CASSCF level. Based on our calculations, seven O‐loss predissociation processes of the C²Σ⁺ state are suggested and an appearance potential value of 7.13 eV for the CS⁺ + O product group is predicted. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

150−230 nm Chemiluminescence from C,CN and CO and observation of C(3P, 1D) in the N/C2F4 and N/O2/C2F4 reactions

Addition of C₂F₄ to a flowing nitrogen afterglow gives rise to CN(E²ΣA²Π, X²Σ), CN(F² ΔA²Π) and C (156.1, 165.5 and 193.0 nm) chemiluminescence. Transitions have been observed from CN(E²Σ) up to ν′ = 2 from which vibrational constants for this state have been recalculated to be ω_eχ_e = 13.8 cm^?1 and ω_e = 1698.4 cm^?1. Ground state and metasrable C(³P, ¹D) have been detected and studied via resonance fluorescence. Addition of O₂ to the N/C₂F₄ reaction system reduces C and CN emission intensities and [C] while giving rise to CO(a³Π-X¹Σ), CO(A¹ΠX¹Σ) and NO(B²ΠX²Π) emission. Probable excitation mechanisms are discussed.     

Theoretical study of electronic structure of rhodium mononitride and interpretation of experimental spectra

Potential energy curves of 22 electronic states of RhN have been calculated by the complete active space second‐order perturbation theory method. The X¹Σ₀⁺ is assigned as the ground state, and the first excited state a³Π₀+ is 978 cm^?1 higher. The ¹Δ(I) and B¹Σ⁺ states are located at 9521 and 13,046 cm^?1 above the ground state, respectively. The B¹Σ⁺ state should be the excited state located 12,300 cm^?1 above the ground state in the experimental study. Moreover, two excited states, C¹Π and b³Σ⁺, are found 14,963 and 15,082 cm^?1 above the X¹Σ⁺ state, respectively. The transition C¹Π₁–X¹Σ₀⁺ may contribute to the experimentally observed bands headed at 15,071 cm^?1. There are two excited states, D¹Δ and E¹Σ⁺, situate at 20,715 and 23,145 cm^?1 above the X¹Σ⁺ state. The visible bands near 20,000 cm^?1 could be generated by the electronic transitions D¹Δ₂–a³Π₁ and E¹Σ⁺₀–X¹Σ⁺₀ because of the spin–orbit coupling effect. © 2013 Wiley Periodicals, Inc.     

First observation of the M 2Σ+ → E2Σ+ (0—0) transition in NO

The emission spectrum of NO excited by electric discharge has been recorded with a high-resolution Fourier transform interferometer. Strong perturbations are observed in the spectrum of the transition M²Σ⁺→ E²Σ⁺ (0—0), due to mixing of the Rydberg state M²Σ⁺(v = 0) with valence states B²Π(v = 22, 23) and L²Π(v = 3). Accurate energies for the M²Σ⁺ rotational levels are given.     

Electronic,spectra, and spin orbit interaction for FrAr van der Waals system

The potential energy curves and spectroscopic constants of the ground and many excited states of the FrAr van der Waals system have been determined using a one‐electron pseudopotential approach. The Fr⁺ core and the electron–Ar interactions are replaced by effective potentials. The Fr⁺Ar core–core interaction is incorporated using the accurate CCSD(T) potential of Hickling et al. (Phys. Chem. Chem. Phys. 2004, 6, 4233). This approach reduces the number of active electrons of the FrAr van der Waals system to only one valence electron, which permits the use of very large basis sets for the Fr and Ar atoms. Using this technique, the potential energy curves of the ground and many excited states are calculated at the self consistent field (SCF) level. In addition, the spin–orbit interaction is also considered using the semiempirical scheme for the states dissociating into Fr (7p) and Fr (8p). The FrAr system is not studied previously and its potential interactions, spectroscopic constants and dipole functions are presented here for the first time. Furthermore, we have predicted the X²Σ⁺–A²Π_1/2, X²Σ⁺–AΠ_3/2, X²Σ⁺–B²Σ_1/2⁺, X²Σ⁺–3²Π_1/2, X²Σ⁺–3²Π_3/2, and X²Σ⁺–5²Σ_1/2⁺ absorption spectra. © 2012 Wiley Periodicals, Inc.     

Chemiluminescence of CaCl From the Ca+Cl2 Reaction in Argon Matrix

Visible chemiluminescence in the 5800-6600 Å region was observed from the Ca+Cl₂ reaction in an argon matrix. The longer wavelength doublet progression is assigned as the A²Π_{3/2, 1/2}→X²Σ⁺ transition of CaCl, with v₀₀= 16189 and 16126 cm^?1, respectively. Emission from the vibrationally excited v' = 1 level of the A state was also observed. This is the first observation of resolved spin-orbit components in matrix chemiluminescent reactions. The progression with v₀₀=16855 cm^?1 was assigned as the B²Σ⁺→X²Σ⁺ transition of CaCl. Both transitions showed very small matrix shifts in the T₂ values. A weak band at 17185 cm^?1 was assigned as either the E²Σ→B²Σ⁺ or the a⁴Σ⁺→A²Π transition of CaCl. Ca atomic emission at 4232 and 6574 Å was also observed and it was attributed to the energy transfer processes from excited CaCl radicals.     

Resonant two-photon ionization of LiNa. Observation and preliminary characterization of five new singlet states

Supersonic molecular beams containing rotationally and vibrationally cold LiNa were probed by one- and multi-photon ionization. Results include determination of a vertical ionization potential (5.05 ± 0.04 eV) as well as first observation of five new singlet states. Preliminary spectroscopic constants (Te, w_e and w_ex_e) and term symbols are reported for these five states (A ¹Σ⁺, C¹ Σ⁺, D ¹Π, E¹ Σ⁺ and F¹ E⁺).     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

Contraction of the well-tempered Gaussian basis sets: The first-row diatomic molecules

The well-tempered Gaussian basis sets (14s 10p) for atoms from lithium to neon were contracted and used in restricted Hartree–Fock calculations on 13 systems: Li₂(Σ), B₂(Σ), C₂(Σ), N₂(Σ), O₂(Σ), F₂(Σ), Ne₂(Σ), LiF(Σ), BeO(Σ), BF(Σ), CN^?(Σ), CO(Σ), and NO⁺(Σ). Spectroscopic constants (R_e, ω_e, ω_ex_e, B_e, α_e, and k_e) and one-electron properties (dipole, quadrupole, and octupole moments at the center of mass and electric field, electric field gradient, potential, and electron density at the nuclei) were evaluated and compared with the Hartree–Fock results. The largest contracted basis set (7_s6_p3_d) gives results very close to the Hartree–Fock values; the remaining differences are attributed to the absence of the f functions in the present basis sets. For Ne₂, the interaction energy was calculated; the magnitude of the basis-set superposition error was found to be very small (less than 3 μE_h at 2.8 a₀ and less than 2 μE_h at 5.0 a₀).     

Bond functions in molecular excited states: MRD CI calculations for the A3Σ+u,B3Πg and W3Δu states of N2

Using double-zeta plus polarization (DZP) basis sets systematically augmented with a variety of bond functions, the term dissociation energies are calculated for the A³Σ⁺_u, B³Π_g and W³Δ_u states of N₂. It is found that the best agreement with literature values is generally with a basis set composition of DZP augmented by a set of s, p and d orbitals at the bond midpoint. The excited state potential energy curves and spectroscopic constants for the B³Π_g state are calculated from this basis and compared with experimental values. Good agreement was obtained, considering the small basis set size, with the spectroscopic constants ω_e, ω_eχ_e, ω_ey_e, B_e and α_e and the dissociation energy D_e (e.g., D_e = 3.38 (3.681, exp.), 4.75 (4.897) and 4.77(4.873) eV for the A, B and W stages, respectively). Poorer agreement was obtained for the term energy T′₀ (7.92 versus 7.35 eV, exp., for the B state). The error in term energy arises largely from an error in the calculated ⁴S → ²D splitting (2.705 versus 2.383 eV, exp.), and shifting the potential curve for the B state by a constant amount leads to much improved agreement relative to the ground state. The counterpoise correction applied to the potential curve of the B state causes a drastic deterioration of the results and shows qualitatively incorrect behaviour, and is therefore not recommended for calculations of this type.     

Electronic structure and bonding of Be2

Laser-induced fluorescence of Be₂ produced by laser vaporization of the metal is observed and analyzed. The X¹Σ_g⁺ ground state is characterized by r_e = 2.45 A and D_e = 790 ± 30 cm^?1. The spectroscopic constants and lifetimes of the much more strongly bound A ¹Πu and B ¹Σ_g⁺ states are also obtained. The Be₂ molecular properties and bonding are discussed and compared with related species.     

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     

Multireference configuration interaction study on spectroscopic parameters and molecular constants of PO and PO+

The highly accurate valence internally contracted multireference configuration interaction (MRCI) approach has been employed to investigate the potential energy curves (PECs) for the X²Π, b⁴Σ^?, C²Σ^? states of PO and the X¹Σ⁺ state of PO⁺. For these electronic states, the spectroscopic parameters of the isotopes (P¹⁶O, P¹⁸O, P¹⁶O⁺, and P¹⁸O⁺) have been determined and compared with those of the investigations reported in the literature. The comparison shows that excellent agreement exists between the present results and the available experiments. With the PECs determined here, the first 30 vibrational states for P¹⁶O(X²Π, b⁴Σ^?), P¹⁸O(X²Π, b⁴Σ^?), P¹⁶O⁺(X¹Σ⁺), and P¹⁸O⁺(X¹Σ⁺) are computed when the rotational quantum number J equals zero (J = 0). The vibrational level G(υ), inertial rotation constant B_υ and centrifugal distortion constant D_υ are determined when J = 0. All the results of vibrational states except for P¹⁶O (X²Π) are reported for the first time. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Electronic transition moment of the AΠr-XΣ system of TiN

The A²Π_r-X²Σ⁺ transition of TiN was observed by the dispersed laser induced fluorescence (DLIF) spectroscopy. The relative intensities of the DLIF spectra were analyzed to determine the dependence of the electronic transition moment, R_e(r), on the internuclear distance, r, as R_e(r)∝{1−0.281(26)r} (1.380 Å≤r≤1.823 Å). This r-dependence was analyzed simultaneously with the reported values of the spin-orbit constants for A²Π_r and the hyperfine-coupling constants for X²Σ⁺ to evaluate the ionic character of the TiN bond, the 4s atomic character in the 9σ orbital of X²Σ⁺, and the 4p atomic character in the 4π orbital of A²Π_r. These characters were confirmed to be in accordance with the reported theoretical prediction. A strong r-dependence was indicated for the 3d-4p mixing in the A²Π_r state due to the configuration mixing of the Ti(3d⁴) and Ti(3d³4p) states at a large internuclear distance.     

CEPA calculations on open-shell molecules

Ab initio calculations at SCF and CEPA levels using large Gaussian basis sets have been performed for the two lowest electronic states,X ² Σ⁺ andA ² Π, of HeAr⁺. Spin-orbit coupling (SOC) effects have been added using a semiempirical treatment. The resulting potential curves for the three statesX,A ₁, andA ₂ have been used to evaluate molecular constants such as vibrational intervals ΔG(v + 1/2) and rotational constantsB _v as well as — by means of a Dunham expansion — equilibrium constants such asR _e , ω _e ,B _e etc. Comparison with the experimental data from UV emission spectroscopy shows that the calculated potential curves are slightly too shallow and have too large equilibrium distances:D _e = 242 cm^?1 andR _e = 2.66 Å compared to the experimental values of 262 cm^?1 and 2.585 Å, respectively, for theX ²Σ⁺ ground state. However, the ab initio calculations yield more bound vibrational levels than observed experimentally and allow for a more complete Dunham analysis, in particular for theA ₂ state. The experimental value of 154 cm^?1 for the dissociation energyD _e of this state is certainly too low; our best estimate is 180±5 cm^?1. For theA ₁ state our calculations are predictions since this state has not yet been observed experimentally.     

LIF measurement of the vibrational dependence of the N2(B 3Π g ) hyperfine splitting parameters

From very high resolution (8 MHz FWHM) LIF measurements, the hyperfine coupling constants of N₂(A ³Σ _u ⁺ ) and N₂(B ³Π _g ) have been obtained for three pairs of vibrational quantum numbersv′,v″. TheA-state constants are in very good agreement with accurate literature data. The vibrational dependence of some of theB-state constants is found to be much more pronounced. This is qualitatively explained in terms of the electronic structure of the two states.