Ab initio calculations on the ground and excited states of InI

Potential energy curves (PECs) of the ground and the low-lying excited states of the InI molecule are computed using the internally contracted multireference singles and doubles configuration interaction with the Davidson correction (ic-MR-CISD + Q) method based on the relativistic effective core potentials (RECPs). The spectroscopic constants are obtained, including the excitation energy (T _e), the equilibrium bond distance (R _e), the dipole moment (μ_e) and the vibrational constants (ω_e and ω_e). Finally, we predict the transition dipole moments, the radiative lifetimes, and the Franc-Condon factors for the transitions of A³Π₀+ ? X¹Σ₀ ⁺ and B³Π^l ? X¹Σ₀ ⁺,. The results reveal that A³Π₀+ and B³Π_l are long-lived states with the lifetimes being of the order of microseconds.     

An ab initio investigation of the low-lying electronic states of BeH

Potential energy curves(PECs) for the ground state(X 2 Σ +) and the four excited electronic states(A 2 Π,B 2 Π,C 2 Σ +,4 Π) of a BeH molecule are calculated using the multi-configuration reference single and double excited configuration interaction(MRCI) approach in combination with the aug-cc-pVTZ basis sets.The calculation covers the internuclear distance ranging from 0.07 nm to 0.70 nm,and the equilibrium bond length R e and the vertical excited energy T e are determined directly.It is evident that the X2Σ+,A2Π,B2Π,C2Σ+ states are bound and 4Π is a repulsive excited state.With the potentials,all of the vibrational levels and inertial rotation constants are predicted when the rotational quantum number J is set to be equal to zero(J = 0) by numerically solving the radial Schr¨odinger equation of nuclear motion.Then the spectroscopic data are obtained including the rotation coupling constant ω e,the anharmonic constant ωexe,the equilibrium rotation constant Be,and the vibration-rotation coupling constant αe.These values are compared with the theoretical and experimental results currently available,showing that they are in agreement with each other.     

用MRCI方法研究CS+同位素离子X2Σ+和A2Π态的光谱常数与分子常数

利用内收缩多参考组态相互作用方法和价态范围内的最大相关一致基aug-cc-pV6Z, 在0.05—0.60 nm的核间距范围内计算了CS⁺离子X²Σ+和A²Π态的势能曲线. 利用CS⁺离子的势能曲线并在同位素质量修正的基础上, 拟合出了X²Σ+和A²Π态的同位素离子^{1 关键词： 同位素识别 势能曲线 光谱常数 分子常数}     

MRCI+Q理论研究SiSe分子X1Σ+和A1Π电子态的光谱常数和分子常数

采用Davidson修正的内收缩多参考组态相互作用方法(MRCI+Q)及相关一致基aug-cc-pV5Z和aug-cc-pVQZ分别计算了SiSe分子X¹Σ⁺和A¹Π电子态的势能曲线. 为提高势能曲线的计算精度, 利用两点总能量外推公式, 将两个电子态的势能曲线外推至完全基组极限, 并对其进行了标量相对论修正, 相对论效应是在cc-pV5Z基组水平下使用三级Douglas-Kroll-Hess哈密顿算符计算的. 利用MRCI+Q/Q5+DK理论水平的势能曲线获得了这两个态的光谱常数(T_e, D_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e和α_e)和J=0时前30个振动态的B_υ和D_υ等分子常数. 其值与已有的实验结果非常一致. 本文得到的光谱常数和分子常数达到了很高精度, 能为进一步的光谱实验和理论研究提供可靠参考. 关键词： 势能曲线 基组外推和标量相对论修正 光谱常数 分子常数     

MRCI study on spectroscopic and molecular properties of several low-lying electronic states of the CN radical

The potential energy curves (PECs) of eight low-lying electronic states (X²Σ⁺, A²Π, B²Σ⁺, a⁴Σ⁺, D²Π, E²Σ⁺, 1²Σ⁻ and F²Δ) of the CN radical have been studied using the ab initio quantum chemical method. The calculations have been performed using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation-consistent basis sets of Dunning and co-workers. The effects on the PECs by the core-valence correlation and relativistic corrections are taken into account. The way to consider the relativistic correction is to use the second-order Douglas-Kroll Hamiltonian approximation. The core-valence correlation correction calculations are performed with the cc-pCVQZ basis set. The relativistic correction is carried out at the level of cc-pV5Z basis set. In order to obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). The PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. With these PECs, the spectroscopic parameters (T_e, R_e, ω_e, ω_ex_e, ω_eу_e, B_e, α_e and γ_e) are determined and compared with those reported in the literature. Finally, with the PECs obtained by the MRCI+Q/CV+DK+Q5 calculations, the complete vibrational states are computed for the eight electronic states by solving the ro-vibrational Schrödinger equation for the non-rotating radical, and the vibrational levels and inertial rotation and centrifugal distortion constants of the first 11 vibrational states are reported, which agree favorably with the available experimental data. The spectroscopic parameters of 1²Σ⁻ and F²Δ electronic states obtained by the MRCI+Q/CV+DK+Q5 calculations should be good predictions for future laboratory experiments.     

Diagnosis of OH radical by optical emission spectroscopy in a wire-plate bi-directional pulsed corona discharge

The emission spectrum of the molecule OH (A²Σ→X²Π, 0–0) during a high-voltage, bi-directional pulsed corona discharge consisting of a gas mixture of N₂ and H₂O in a wire-plate reactor has been successfully recorded under severe electromagnetic interference at atmospheric pressure. The relative vibrational populations and the vibrational temperature of N₂ (C, v′) have also been determined. Due to the difficulty of determining the exact overlapping spectral line shape function of the OH (A²Σ→X²Π, 0–0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g), a practicable Gaussian form is used for calculating the emission intensity of OH (A²Σ→X²Π, 0-0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g). The emission intensity of OH (A²Σ→X²Π, 0–0) has been evaluated with a satisfactory accuracy by subtracting the emission intensity of the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g) from the overlapping spectra. The relative population of OH (A²Σ) has been obtained by the emission intensity of OH (A²Σ→X²Π, 0–0) and Einstein's transition probability. The influences of peak voltage, pulse repetition rate and O₂ flow rate on the relative population of OH (A²Σ) radicals have also been investigated. We found that the relative population of OH (A²Σ) rises with an increase in both the peak applied voltage and the pulse repetition rate. When oxygen is added to an N₂ and H₂O gas mixture, the relative population of OH (A²Σ) radicals decreases exponentially with an increase in added oxygen. The main physicochemical processes involved are also discussed in this paper.     

LiC分子基态及其低电子激发态的多参考组态相互作用方法研究

采用包含Davidson修正的多参考组态相互作用(MRCI+Q)方法结合6-311++G(3df,3pd)基组计算了LiC分子基态(X4Σ-)以及五个低电子激发态(a2Π,b2Δ,c2Σ-,d2Σ+,A4Π)的势能曲线.将得到的势能曲线拟合到Murrell-Sorbie解析势能函数形式,确定了对应态的平衡结构Re、谐振频率ωe和离解能De等光谱数据,计算值与仅有的几个其他结果进行了比较.通过求解核运动的薛定谔方程首次报道了LiC分子几个低电子态在J=0下的振动能级、转动惯量和六个离心畸变常数(Dν,Hν,Lν,Mν,Nν和Oν).     

Isotope shift studies in the spectrum of boron monosulphide

The spectrum of boron monosulphide has been excited in microwave discharge and photographed at moderate dispersion. TheC ²Π _r ?X ²Σ⁺,B ²Σ⁺?A ²Π _i andA ²Π _i ?X ²Σ⁺ band systems extending from 2100–9000 Å have been obtained for B³²S and B³⁴S species. Isotope shifts for all these band systems have been measured. Comparison of the observed isotope shifts with the theoretically calculated isotope shifts confirms the emitter as well as the vibrational assignments of all these band systems.     

Extensive spectroscopic calculations on 12 low-lying electronic states of AlN molecule including transition properties

Using the CASSCF method followed by the internally contracted MRCI approach in combination with the correlation-consistent basis sets, the potential energy curves (PECs) are calculated for the X³Π, A³Σ^-, B³Σ⁺, C³Π, E³Δ, a¹Σ⁺, b¹Π, c¹Δ, d¹Σ⁺, e¹Π, 2³Σ^? and 3³Σ^? electronic states of AlN molecule for internuclear separations from 0.1 to 1.0 nm. All the electronic states correlate to the three dissociation channels, Al(²P_u) + N(⁴S_u), Al(²P_u) + N(²D_u) and Al(²P_u) + N(²P_u). Of these 12 electronic states, only the 2³Σ^? possesses the double well. The PECs determined by the internally contracted MRCI approach are corrected for size-extensivity errors by means of the Davidson correction. The convergent behavior of present calculations is observed with respect to the basis set and level of theory. The effect of core-valence correlation and scalar relativistic corrections on the spectroscopic parameters is discussed. Scalar relativistic correction calculations are performed by the third-order Douglas-Kroll Hamiltonian approximation at the level of cc-pVTZ basis set. Core-valence correlation corrections are included with a cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated by fitting the first ten vibrational levels when available, which are obtained by solving the ro-vibrational Schrödinger equation with the Numerov’s method. The spectroscopic parameters are compared with those reported in the literature. Excellent agreement is found between the present results and the measurements. Analyses show that the spectroscopic parameters reported in this paper can be expected to be reliably predicted ones. The Franck-Condon factors and radiative lifetimes of the transitions from the A³Σ^?, B³Σ⁺, C³Π, a¹Σ⁺ and b¹Π electronic states to the ground state are calculated for several low vibrational levels, and some necessary discussion has been made.     

Electronic states of SiF and SiF+: Configuration-interaction studies

For SiF, low-lying ²Π, ⁴Π, ²Σ⁺, ⁴Σ⁺, ²Σ⁻, ⁴Σ⁻, ²Δ, and ⁴Δ states were studied by configuration-interaction methods, using a double-zeta plus polarization basis set with 4s, 4pσ, 4pπ, and 5pπ Rydberg orbitals. Potential energy curves and spectroscopic constants for 17 stable valence and Rydberg states are given. The lowest ²Σ⁻ state is repulsive. There is good agreement with known spectroscopic constants. Besides A²Σ⁺, another semidiffuse state, 1⁴Π, is predicted. For the isoelectronic PO molecule, 2π → 3π valence excitations lie below Rydberg excitations, such that 2²Π of PO derives from 2π → 3π, whereas 2²Π of SiF derives from 3π → 4pπ. Dipole moments of X²Π and A²Σ⁺ at their respective R_e, and the radiative lifetime of A²Σ⁺ were calculated. For SiF⁺, many electronic states were investigated, but only two, the X¹Σ⁺ ground state and 1³Π are found to be stable. The ionization energy of SiF is calculated to be 6.87 eV (adiabatic) and 7.05 eV (vertical).     

Effects on spectroscopic properties for several low-lying electronic states of CS molecule by core-valence correlation and relativistic corrections

The potential energy curves (PECs) of six low-lying electronic states (X¹Σ⁺, a³Π, a′³Σ⁺, d³Δ, e³Σ⁻ and A¹Π) of CS molecule have been investigated using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach with large correlation-consistent basis sets. Effects on the PECs by the core-valence correlation and relativistic corrections have been taken into account. And the two corrections are performed at the level of cc-pV5Z basis set. The way to consider the relativistic corrections is to use the second-order Douglas-Kroll Hamiltonian approximation. Using the CCSD(T), MRCI and MRCI with the Davidson modification (MRCI + Q), the PECs of electronic states involved are extrapolated to the complete basis set (CBS) limit. With the PECs, the spectroscopic parameters (T_e, R_e, ω_e, ω_ex_e, ω_ey_e, α_e, β_e, γ_e and B_e) of the six low-lying electronic states are determined. These parameters are in excellent agreement with the experimental data. The complete vibrational states are computed for the six low-lying electronic states when the rotational quantum number J equals zero, and the inertial rotation constants of the first 23 vibrational states are reported, which agree favorably with the RKR data. Comparison with the measurements shows that the two-point total-energy extrapolation scheme can obviously improve the quality of spectroscopic parameters and molecular constants.     

Low-lying electronic states of BeH+ with the effect of inner electrons

The potential energy curves of the low-lying electronic states of BeH⁺ molecular ion are performed by using highly accurate multi-reference configuration interaction with AV5Z basis sets for H atom and ACV5Z basis set for Be atom, 1s inner shell of Be is considered as the core orbit and the active orbit, respectively, which are used to characterise the spectroscopic properties of a manifold of singlet and triplet states. Fourteen electronic states correlated with eight dissociation channels are investigated, we have found that the a³Σ⁺ and c³Σ⁺ both are bound states, the 3³Σ⁺ possesses double wells, and the C¹Σ⁺, 3³Σ⁺, 2³Π, 2¹Π, 1¹Δ, 1³Δ, 2³Δ and 2¹Δ states are studied for the first time. Transition dipole moment, Franck–Condon factors q_υ′υ^″ and Einstein coefficients A_υ′υ^″ for A¹Σ⁺–X¹Σ⁺, 2¹Π–B¹Π, c³Σ⁺–a³Σ⁺ and b³Π–a³Σ⁺ systems have been calculated. Radiative lifetime of A¹Σ⁺–X¹Σ⁺ band system has also been determined.     

分子部分电子态的高阶振动能级和离解能的精确研究

鉴于K₂分子电子态的振动能谱和分子离解能D_e在实际研究和应用中的重要性,应用Sun,Ren等人提出的基于微扰理论的代数方法(AM)和基于AM的代数能量方法(AEM)研究了K₂分子的X¹Σ⁺_g,a³Σ⁺_u,0^-_g,B¹Π_{u< 关键词： 2}分子')" href="#">K₂分子 代数方法 高阶振动能级 离解能     

A photoelectron spectroscopic study of the second ionisation of the CF(X2Π) radical

The CF(X²Π) radical has been re-investigated with vacuum ultraviolet photoelectron spectroscopy. Two bands were observed and assigned to the ionisations CF⁺(X¹Σ⁺)←CF(X²Π) and CF⁺(a³Π)← CF(X²Π). The first band, which has been observed previously, has an adiabatic ionisation energy of (9.11±0.02) eV and a vertical ionisation energy of (9.55±0.02) eV. For the second band, three vibrational components were observed with the first, the most intense, at an ionisation energy of (13.94±0.02) eV. Analysis of the vibrational structure in the two observed bands allowed ω_e and r_e to be determined as 1810±30 cm⁻¹ and 1.154±0.005 Å, respectively for the first ionic state, CF⁺(X¹Σ⁺), and 1614±30 cm⁻¹ and 1.213±0.005 Å, respectively for the second ionic state, CF⁺(a³Π). Comparison of the ionisation energies and spectroscopic constants obtained has been made with values obtained from recent multi-reference configuration interaction calculations.     

AsO+同位素离子X2∑+和A2∏电子态的多参考组态相互作用方法研究

采用包含Davidson修正多参考组态相互作用(MRCI)方法结合价态范围内的最大相关一致基As/aug-cc-pV5Z和O/aug-cc-pV6Z, 计算了AsO⁺ (X²∑⁺)和AsO⁺(A²∏)的势能曲线. 利用AsO⁺离子的势能曲线在同位素质量修正的基础上, 拟合出了同位素离子⁷⁵As¹⁶O⁺和⁷⁵As¹⁸O⁺的两个电子态光谱常数. 对于X²∑⁺态的主要同位素离子⁷⁵As¹⁶O⁺, 其光谱常数R_e, ω_e, ω_ex_e, B_e和α_e分别为 0.15770 nm, 1091.07 cm^-1, 5.02017 cm^-1, 0.514826 cm^-1和0.003123 cm^-1; 对于A²∏态的主要同位素离子⁷⁵As¹⁶O⁺, 其T_e, R_e, ω_e, ω_ex_e, B_e和α_e分别为5.248 eV, 0.16982 nm, 776.848 cm^-1, 6.71941 cm^-1, 0.443385 cm^-1和0.003948 cm^-1. 这些数据与已有的实验结果均符合很好. 通过求解核运动的径向薛定谔方程, 找到了J=0时AsO⁺(X²∑⁺)和AsO⁺(A²∏)的前20个振动态. 对于每一振动态, 还分别计算了它的振动能级、转动惯量及离心畸变常数, 并进行了同位素质量修正, 得到各同位素离子的分子常数. 这些结果与已有的实验值非常一致. 本文对于同位素离子⁷⁵As¹⁶O⁺(X¹∑⁺), ⁷⁵As¹⁸O⁺(X¹∑⁺), ⁷⁵As¹⁶O⁺(A¹∏)和⁷⁵As¹⁶O⁺(A¹∏)的光谱常数和分子常数属首次报导.     

Ab initio study of PN electronic states – a qualitative interpretation of the perturbation and predissociation effects on observed transitions

Valence and high electronic states of PN have been calculated with accurate quantum chemistry methods. The variety of theoretical methods used includes complete active space self-consistent field, multireference configuration interaction and the newly developed explicitly correlated coupled cluster methods. The large correlation-consistent atomic orbitals basis sets AVQZ, AV5Z and AV(5+d)Z are used for the potential energy curves calculations in the bonding and long-range regions. The spectroscopic constants (R_e, B_e, ω_e, ω_ex_e, α_e, D_e, T_e) and the vibrational levels of the bound valence states (X¹Σ⁺, A¹Π, a³Σ⁺, d ³Δ, e³Σ^?, C¹Σ^?, b³Π, D ¹Δ and E¹Σ⁺ and some higher bound states) are determined and compared with experimental findings when available. Significant spin–orbit interactions between triplet states and A¹Π and E¹Σ⁺ excited states are found near the crossing points of the potential energy curves and could explain predissociation phenomena and the perturbations of the vibrational levels experimentally observed for PN in their A¹Π and E¹Σ⁺ states.     

Rotational Analysis of the 1–4 Band of the B 2Σ+–X 2Σ+ System of 14C16O+

ABSTRACT

High-resolution emission spectrum of the 1–4 band of the B ²Σ⁺–X ²Σ⁺ transition of ¹⁴C¹⁶O⁺ was observed for the first time by conventional emission spectroscopy. The band spectrum was excited in a water-cooled Geissler lamp filled with commercial gaseous carbon monoxide enriched in about 80% of the radiocarbon ¹⁴C. A rotational analysis has been carried out and obtained molecular constants have been merged with previously published data for the B ²Σ⁺–A ²Π_i and A ²Π_i–X ²Σ⁺ transitions. The principal equilibrium constants for the ground X ²Σ⁺ state obtained from this work are ω_e = 2121.7726(98), ω_e x _e = 13.9055(27), B _e = 1.815290(30), α_e = 1.6594(33) × 10^?2, and γ_e = ? 0.377(73) × 10^?4 cm^?1. Also, presently known experimental equilibrium molecular constants of the X ²Σ⁺ states of the CO⁺ isotopic molecules are summarized and isotopic dependence of the B _e and ω _e constants is discussed.     

The use of electron impact dissociation and the photon-photon cascade technique to measure the lifetime of the B2Σ+ state of CN

The lifetime of the (B³Σ⁺_{υ= 0, 1} state of the CN radical has been measured by the photon-photon delayed coincidence technique, the CN radical being produced by electron impact dissociation of acetonitrile. This is the first lifetime measurement in a free radical by this method. The optical cascade in the band spectrum of CN used for the present measurement is H²Π_r - B²Σ⁺ - X²Σ⁺. The lifetime of the (B²Σ⁺)_{υ=0, 1} state in CN has been found to be 61.1 ± 7.6 ns.     

Spectroscopic and molecular properties of 14 selected electronic states of Si2 molecule

The potential energy curves (PECs) of the X³Σ_g⁻, D³Π_u, a¹Δ_g, b¹Π_u, H′³Σ_u⁻, K³Σ_u⁻, 1³Σ_u⁺, 1³Π_g, 2³Σ_u⁺, 2³Π_g, 3³Π_g, 3³Σ_u⁺, 2³Π_u and 2³Σ_g⁻ electronic states of the Si₂ molecule are investigated using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach with the correlation-consistent basis sets of Dunning and co-workers. The effects on the PECs by the core-valence correlation and relativistic corrections are included. The way to consider the relativistic correction is to use the third-order Douglas-Kroll Hamiltonian approximation. The core-valence correlation correction is made with the aug-cc-pCV5Z basis set. And the relativistic correction is performed at the level of cc-pV5Z basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). The PECs of all these electronic states are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. Using the PECs, the spectroscopic parameters are determined and compared with those reported in the literature. With these PECs determined by the MRCI+Q/CV+DK+56 calculations, the vibrational levels and inertial rotation constants of the first 20 vibrational states are evaluated and compared with the RKR data for these electronic states when the rotational quantum number J equals zero. On the whole, as expected, the most accurate spectroscopic parameters and molecular constants of the Si₂ molecule are determined by the MRCI+Q/CV+DK+56 calculations. And the spectroscopic parameters of the 1³Σ_u⁺, 1³Π_g, 2³Σ_u⁺, 2³Π_g, 3³Π_g, 3³Σ_u⁺, 2³Π_u and 2³Σ_g⁻ electronic states obtained by the MRCI+Q/CV+DK+56 calculations should be good prediction for future laboratory experiment.     

Time evolution of the Infrared Laser Induced Breakdown Spectroscopy of DNA bases Guanine and Adenine

Laser-Induced Breakdown Spectroscopy (LIBS) of DNA bases Guanine and Adenine was studied using a high-power CO₂ pulsed laser (λ=10.591 μm, τ _FWHM=64 ns and fluences ranging from 25 to 70 J/cm²). The strong emission of the adenine and guanine plasma, collected using a high-resolution spectrometer, at medium-vacuum conditions (4 Pa) and at 1 mm from the target, exhibits excited molecular bands of CN (B² Σ ⁺–X² Σ ⁺) and excited neutral H and ionized N⁺ and C⁺. The medium-weak emission is due to excited species C²⁺, C³⁺, N, O, O⁺, O²⁺ and molecular band systems of $\mathrm{C}_{2}(\mathrm{d}^{3}\varPi_{\mathrm{g}}\mbox{--}\mathrm{a}^{3}\varPi_{\mathrm{u}};\ \mathrm{D}^{1}\varSigma_{\mathrm{u}}^{+}\mbox{--}\mathrm{X}^{1}\varSigma_{\mathrm{g}}^{+})$ , OH(A² Σ ⁺–X² Π), NH(A³ Π–X³ Σ ^?), CH(A² Π–X² Π), $\mathrm{N}_{2}^{+}(\mathrm{B}^{2}\varSigma_{\mathrm{u}}^{+}\mbox{--} \mathrm{X}^{2}\varSigma_{\mathrm{g}}^{+})$ and N₂(C³ Π _u–B³ Π _g). We focus our attention on the temporal evolution of different atomic/ionic and molecular species. The velocity distributions for various (different) species were obtained from time-of-flight (TOF) measurements. Intensities of some lines from C⁺ were used for determining electron temperature and their Stark-broadened profiles were employed to estimate the temporal evolution of electron density.